Exam 3 (11/9/17)
Like air in the atmosphere, water in a pipe has...
-A density and a weight per volume -A pressure gradient when it is at equilibrium -Its pressure decrease with altitude -Its weight supported by that pressure gradient
What happens when air flows nearest the ball's surface?
-Experience viscous drag forces -Converts kinetic energy into thermal -Stops or stalls if it runs out of total energy
What happens when air flows into the rising pressure behind the ball?
-It decelerates -Converts kinetic energy into pressure potential
How do turbofan engines obtain forward momentum?
-Moving much more air -Giving that air less energy
How do turbojets obtain forward momentum?
-Moving relatively little air -Giving that air too much energy
Water flowing along a single streamline in SSF has...
-PPE, KE, and GPE -Must have a constant total energy per volume -Obeys Bernoulli's Equation (with gravity)
How do you deliver water to a pipe with no gravity?
-Squeeze water to increase its pressure until that pressure exceeds the pressure in the pipe. -The water will then accelerate toward the pipe. -Pressurized water will flow into the pipe
How do you use work to pump water?
-You squeeze the water inward - the force. -The water moves inward - the distance. -The work you do pumping water is: work = pressure · volume
What is the atmospheric pressure of earth?
14.7psi or 1.01 x 10⁵ N/m² (pascals)
Room temperature is approximately ___ K.
300
Archimedes' Principle
A balloon immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces
Why doesn't the atmosphere fall or collapse?
A gradient in its pressure supports its weight. -Air has a density, and its pressure is proportional to its density. -The atmosphere is in equilibrium. -Its density and pressure decrease with altitude. -The resulting pressure imbalances support its weight.
Why are there different wing shapes?
Airspeed and performance influence wing design. -Asymmetric airfoils produce large lifts. Are well-suited to low-speed flight -Symmetric airfoils produce small lifts. Are well suited to high-speed flight. Allow plane to fly inverted easily -Some planes change wing shape in flight.
A balloon filled with helium at ordinary pressure contains (more/as many/fewer) particles as the air it displaces
As many
Flow in nozzle develops a pressure gradient with lower pressure & higher speed (at start of nozzle/as the nozzle narrows).
As the nozzle narrows
Ideal Gas Law
Assumes perfectly independent particles pressure = Boltzmann constant ∙ particle density ∙ absolute temperature P = n ∙ Kb ∙ T
Flow in nozzle develops a pressure gradient with higher pressure & lower speed (at start of nozzle/as the nozzle narrows).
At start
What happens during stalling?
At too great an angle of attack, the upper boundary layer stalls, the airstream detaches from wing, the lift decreases dramatically, severe pressure drag appears, and the plane plummets abruptly.
What gas/force is always acting on us?
Atmosphere
Why do balls experience air resistance?
Balls interact with and transfer momentum to air. -When a ball moves through air, drag forces arise. Air pushes ball downstream; ball pushes air upstream. Air transfers downstream momentum to ball. -When a ball deflects passing air, lift forces arise. Air pushes ball to one side; ball pushes air to other side. Air transfers sideways momentum to ball.
Air's density and pressure (decrease/increase) with higher altitude.
Decrease
As a horizontal stream of water hits a wall, its height (GPE) is constant, so its KE (increases/decreases) and its PPE (increases/decreases)
Decreases; increases
Air's pressure is proportional to its _____.
Density
As water flows (downward/upward) in a uniform pipe, its speed (KE) cannot change so its GPE decreases, and its PPE increases
Downward
Gases with equal particle densities and equal temperatures have (unequal/equal) pressures.
Equal
The density of gold is 19.0 times that of water. If you take a gold crown weighing 24.0 N and submerge it in water, what will the buoyant force on the crown be? Answer in N. Density of water = 1000 kg/m³
F = 1.26 N 1. The principle of Archimedes: a floating object displaces the amount of liquid that equals its weight. 2. If the weight of the crown is 24 N then the upward force by similar reasoning = 24(18/19) = 22.74 N 3. Weight - upward force = 1.26
If you submerge an 5.00-kg log in water and it displaces 8.00 kg of water, what will the net force on the log be the moment you let go of the log? Use g=9.81 m/s². Answer with N.
F = 29.4 N 1. Find the net force. 8 kg - 5 kg = 3 kg 2. Multiply by acceleration. 3 x 9.81
How much force is the air exerting on the front surface of the book with dimensions 15.0 x 26.0 cm. Assume atmospheric pressure equal to 100,000. Pa. Answer in N.
F = 3900 N 1. Convert 15 and 26 cm to m. 15 cm = .15 m 26 cm = .26 m 2. Calculate area A = .15 x .26 = .039 3. Solve for P = F/A 100,000 = F/.039 F = 100,000 x .039
As water (rises upward/falls downward) from a spout, its pressure (PPE) stays constant (atmospheric), so its GPE decreases and its KE increases
Falls downward
A balloon filled with hot air at ordinary pressure contains (more/as many/fewer) particles than the air it displaces
Fewer
A surface exposed to air experiences a _____ proportional to its area.
Force
Air pressure is _____ per area.
Force
Air particles bounce around in _____.
Free fall
What causes pressure gradients?
Gravity
Air bends away from ball's back. At back: (low/high) pressure, (fast/slow) flow.
High; low
At (low/high) Reynolds number, the flow is turbulent. Pressure forces also transfer momentum to the ball. The ball also experiences (pressure/viscous) drag.
High; pressure
Air bends away from ball's front. At front: (low/high) pressure, (fast/slow) flow.
High; slow
Squeezing air particles together (increases/decreases) the density, pressure, and weight.
Increases
Water's gravitational potential energy (increases/decreases) with altitude.
Increases
As water sprays horizontally from a nozzle, its height (GPE) is constant, so its KE (increases/decreases) and its PPE (increases/decreases)
Increases; decreases
Deflected flow also leads to _____.
Induced drag
Above ~2300 (inertia/viscosity) wins, so flow is (laminar/turbulent).
Inertia; turbulent
Flow in bent hose develops a pressure gradient with lower pressure & higher speed on the (inside/outside) of the bend
Inside
Why does water move through level pipes?
It accelerates toward lower pressure. -Water, like all fluids, obeys Newton's laws. (When it experiences zero net force, it coasts; experiences a net force, it accelerates) -Pressure imbalances exert net forces on water.
How does an airplane support itself in the air?
It deflects air downward; air pushes it upward. -Air bends away from wing bottom. Air pressure rises, speed drops. -Air bends toward wing top. Air pressure drops, speed rises. -There is an upward pressure force on the wing. -Wing transfers downward momentum to the air.
How much does the diameter of a hose matter?
It matters a surprisingly large amount. -Water flow through a hose is proportional to pressure difference between hose ends, 1/viscosity, 1/hose length, and (hose diameter)⁴ Flow Rate = (π)(pressure difference)(hose diameter⁴)/(128)(hose length)(viscosity)
How does a plane propel itself through the air?
It pushes air backward with its props or engines. -Propellers are spinning wings. They deflect air backward, do work on air (add energy), and pump air toward rear of plane -Jet engines are ducted air pumps and confine the air and pump it toward rear of plane
How does a plane turn?
It uses lift to accelerate in the direction of turn. -Airplane has three orientation controls: Its angle of attack is controlled by elevators. Its left-right tilt is controlled by ailerons. Its left-right rotation is controlled by rudder. -Steering involves ailerons and rudder. -Elevation involves elevators and engine.
Why does a hot air balloon float in cold air?
It weighs less than the air it displaces. -As the temperature of air increases, its particles move faster, bounce harder, and bounce more often and contribute more to air's pressure (because it is hotter than colder air around it) -A balloon filled with hot air at ordinary pressure contains fewer particles than the air it displaces, weighs less than the air it displaces, and experiences a buoyant force that exceeds its weight
Why does a helium balloon float in air?
It weighs less than the air it displaces. -Compared with air, the particles in helium gas are lighter but move faster and bounce more often, and contribute just as much to pressure (at same temperature as the air) -A balloon filled with helium at ordinary pressure contains as many particles as the air it displaces, weighs less than the air it displaces, and experiences a buoyant force that exceeds its weight
Why does the atmosphere push up on a balloon?
Its pressure gradient pushes the balloon upward. -Because of atmospheric structure, air pressure is stronger near the bottom of a balloon weaker near the top of the balloon so the air pushes up harder than it pushes down and this imbalance yields an upward buoyant force.
How does air inflate a rubber balloon?
Its pressure pushes the balloon's skin outward. -Air is a gas and has pressure -Pressure inside a balloon is greater than outside. -Total pressure forces on balloon skin are outward. -Balloon is held taut by those outward pressure forces.
Turbulent flow around a slow ball experiences a (small/large) pressure drag force.
Large
Even in steady-state, water can accelerate, but forward acceleration would (cause jams/leave gaps), and backward acceleration would (cause jams/leave gaps), so the acceleration must involve _____.
Leave gaps; cause jams; turning
A balloon will float if its average density is (more/less) than that of the surrounding air.
Less
Deflected flow causes _____.
Lift
Water accelerates toward (high/low) pressure
Low
Air bends toward ball's sides. At side: (low/high) pressure, (fast/slow) flow.
Low; fast
At (low/high) Reynolds number, the flow is laminar. Only viscous forces transfer momentum to the ball. The ball experiences only (pressure/viscous) drag.
Low; viscous
A helium balloon has the same particle density but a (lower/higher) density than the surrounding air.
Lower
Imbalance pushes surface toward (higher/lower) pressure.
Lower
Particles in a gas contribute equally to pressure. (Lower/Higher)-mass particles move faster and bounce more, so all the effects of particle mass cancel out.
Lower
Water accelerates toward (lower/higher) pressure.
Lower
A hot-air balloon has a (lower/higher) particle density and a (lower/higher) density than the surrounding air.
Lower; lower
Air particles transfer _____ as they bounce.
Momentum
Steady state flow is steady flow in (moving/motionless) surroundings.
Motionless
Why do pipes rattle when you close the faucet?
Moving water carries momentum. -Water transfers its momentum via impulses: impulse = pressure·surface area·time -Large momentum transfers require large pressures, large surface areas, or long times. -Moving water can be surprisingly hard to stop. Sudden stops can result in enormous pressures.
What does absolute zero (0 K) mean in regards to thermal energy?
None is available
Acceleration toward the side (turning) requires _____, and involves pressure _____, and changes in _____.
Obstacles; imbalances; speed
Flow in bent hose develops a pressure gradient with higher pressure & lower speed on the (inside/outside) of the bend.
Outside
The particle density of standard atmospheric air at 283.15 K (10 ˚C) is 2.687x10^25 particles/m³. Using the ideal gas law, calculate the pressure of this air. Use Pa for units. Ideal Gas Law: P = n∙kB∙T kB = 1.38064852 x 10⁻²³
P = 105043 Pa
To dive far below the surface of the water, a submarine must be able to withstand enormous pressures. At a depth of 151 m, what pressure does water exert on the submarine's hull? Use g=9.81 m/s². Answer in Pa. P = P₀ + (density)(g)(height) Density of water = 1000 kg/m³ P₀ = 100,000 Pa
P = 1581310 Pa 1. P = 100000 + (1000∙9.81∙151) 2. P = 100000 + 1481310
If you fill a container with air at room temperature (300 K), seal the container, and then heat the container to 700 K, what will the pressure be inside the container? Assume atmospheric pressure equal to 100,000 Pa. Answer in Pa. Ideal Gas Law: P = n∙kB∙T kB = 1.38064852 x 10⁻²³
P = 233333 Pa 1. P₁ = n₁∙kB₁∙T₁ P₂ = n₂∙kB₂∙T₂ 2. 100,000 = n₁∙kB₁∙300 ? = n₂∙kB₂∙700 3. Remove (cancel out) the values that don't change 100,000 Pa = 300 k ? Pa = 700 k 4. Cross multiply. 300x = 100,000∙700 x = 70,000,000/300
An air compressor is a device that pumps air particles into a tank. A particular air compressor adds air particles to its tank until the particle density of the inside air is 35.0 times that of the outside air. If the temperature inside the tank is the same as that outside, how does the pressure inside the tank compare to the pressure outside? Assume atmospheric pressure equal to 100,000. Pa. Answer in Pa. Ideal Gas Law: P = n∙kB∙T kB = 1.38064852 x 10⁻²³
P = 3,500,000 Pa 1. The only value changing is n →P = n∙kB∙T 2. P₂/P₁ = n₂/n₁ 3. Cross multiply. 1x = 100,000∙35 x = 3,500,000/1
Turbulence causes _____.
Pressure drag
Air pressure decreases with altitude, creating a _____.
Pressure gradient
What type of energy does pumped water carry with it as it moves?
Pressure potential energy
Air's temperature on an absolute scale is _____ to average thermal kinetic energy per particle
Proportional
How can you produce pressurized water?
Push inward on the water, using a surface. -To pressurize water, confine it and squeeze. As you push inward on the water: It pushes outward on you (Newton's third law). Water's outward push is produced by its pressure, so the water's pressure rises as you squeeze it harder. -Water (a liquid) is incompressible. (Its volume remains constant as its pressure increases.)
Jet engines pump air toward the (front/rear) of the plane.
Rear -Air entering duct diffusor exchanges speed for pressure. -A compressor does work on air, increases its pressure. -Fuel is burned in that air, increasing air's energy. -A turbine extracts work from air, decreasing its pressure. -Air exiting duct nozzle exchanges pressure for speed.
Air's temperature on a conventional scale is _____ to average thermal kinetic energy per particle.
Related
Water's energy (increases/remains constant/decreases) during SSF.
Remains constant
Flow type depends on _____.
Reynold's Number RN = inertial influences/ viscous influences or RN = (density)(obstacle length)(speed)/viscosity
As water (rises upward/falls downward) from a fountain nozzle, its pressure (PPE) stays constant (atmospheric), so its GPE increases and its KE decreases
Rises upward
Turbulent flow around a fast ball experiences a (small/large) pressure drag force.
Small
In steady state flow, water flows along _____.
Streamlines
How does air flow around a ball?
That depends on Reynolds number. -At low Reynolds number, the flow is laminar. Only viscous forces transfer momentum to the ball. The ball experiences only viscous drag. -At high Reynolds number, the flow is turbulent. Pressure forces also transfer momentum to the ball. The ball also experiences pressure drag.
As water flows, what happens to its energy?
That energy is converted between several forms. -In SSF, water flows along streamlines. -Water flowing along a single streamline in SSF has both PPE and kinetic energy (KE), must have a constant total energy per volume, and obeys Bernoulli's Equation (no gravity) PPE/V + KE/V = Constant/V
How does the airplane "lift off" the runway?
The airplane sheds a vortex and is lifted upward. -As wing starts moving in air, the airflow is symmetric and the wing experiences no lift -Trailing edge kink is unstable and the wing sheds a vortex -After the vortex leaves, the wing experiences lift.
Why does water pour gently from an open hose?
The free-flowing water wastes most of its energy. -Viscous effects in the hose waste water's total energy as thermal energy and become stronger with increased flow speed -Increasing the speed of the flow in the hose increases the energy wasted by each portion of water and makes the loss of pressure more rapid
Why does water spray fast from a nozzle?
The nozzle causes water to turn PPE into KE. -As water flow necks down in a nozzle, it must speed up to avoid a "traffic jam", have a pressure imbalance pushing it forward, and be flowing from higher pressure to lower pressure
Why does plane tilt up to rise; down to descend?
The wing's angle of attack affects its lift. -A wing's lift depends on the shape of its airfoil and its angle of attack—its tilt relative to approaching air -Tilting an airplane's wings affects lift. Can make the airplane accelerate up or down. Usually requires tilting the airplane's fuselage -Plane's tilt controls lift, not direction of travel.
What keeps the individual atoms and molecules of air separate and in motion?
Thermal energy
Why do spinning balls curve in flight?
They experience two aerodynamic lift forces. -Laminar effect: Magnus force; turning surface pushes/pulls on the air flow. Air on one side makes longer bend toward the ball. -Turbulent effect: Wake deflection force; turning surface alters point of flow separation. Flow separation and wake are asymmetric.
Why do some balls have dimples?
To produce a turbulent boundary layer -Air effected by ball's surface is the boundary layer. -Reynolds # <100,000: laminar boundary layer. Nearest sublayer is slowed relentlessly by viscous drag. -Reynolds # >100,000: turbulent boundary layer. Sublayers tumble and interchange; they help each other. Boundary layer penetrates deeper into rising pressure.
Where does the work you do pumping water go?
To the water at the delivery-end of the pipe -Pressure potential energy is unusual because it is not really stored in the pressurized water, and it is promised by the water's pressure source -In steady state flow (SSF), which is steady flow in motionless surroundings, promised energy is as good as stored energy, so pressure potential energy (PPE) is meaningful
What happens when air nearest the ball stalls?
Turbulence ensues
_____ flow produces thermal energy.
Turbulent
Wake Deflection Force
Turning surface alters point of flow separation
Spinning Balls and Wake Force
Turning surface alters point of flow separation. -Flow separation is delayed on one side and hastened on the other side, so wake is asymmetric. The overall air flow is deflected. -Ball pushes air to one side. -Air pushes ball to other side. Ball feels wake deflection force
Magnus Force
Turning surface pushes/pulls on the air flow
Spinning Balls and Magnus Force
Turning surface pushes/pulls on the air flow. -Air on one side makes long bend toward ball. -Air on other side makes shorter bend away from ball. -Pressures are unbalanced. The overall air flow is deflected. -Ball pushes air to one side. -Air pushes ball to other side. Ball feels Magnus force
(Balanced/Unbalanced) pressures exert an overall force.
Unbalanced
A balloon immersed in a fluid experiences an (downward/upward) buoyant force equal to the weight of the fluid it displaces.
Upward
As water flows (downward/upward) in a uniform pipe, its speed (KE) cannot change (a jam or a gap would form), so its GPE increases and its PPE decreases
Upward
If your boat weighs 1010 N, how much water will it displace when it's floating motionless at the surface of a lake? Answer in m³. Density of water = 1000 kg/m³
V = .103 m³ 1. The principle of Archimedes: a floating object displaces the amount of liquid that equals its weight. 2. Weight of displaced water = ma 1010 = m∙9.81 1010/9.81 = m
Fluids are characterized by their _____.
Viscosities
Below ~2300 (inertia/viscosity) wins, so flow is (laminar/turbulent).
Viscosity; laminar
_____ forces oppose relative motion within a fluid and are similar to sliding friction: they waste energy
Viscous
Surface friction causes _____.
Viscous drag
What causes hissing in a faucet, hose, or nozzle?
Water can become turbulent and produce noise. -We have been examining laminar flow in which viscosity dominates the flow's behavior and nearby regions of water remain nearby -Now we'll also consider turbulent flow in which inertia dominates the flow's behavior and nearby regions of water become separated
How does a faucet control flow?
Water's energy and viscosity limit the flow. -Water traverses a narrow passage in the faucet. -Total energy limits flow speed through passage. The water turns its total energy into kinetic energy, but its peak speed is limited by its initial pressure. -Motion near surfaces slows water in the passage. Because water at the passage walls is stationary, viscous forces within the water slow all of it.
Water settles to the bottom of a tank of gasoline. Which takes up more space: 1 kg of water or 1 kg of gasoline? a. 1 kg of gasoline because gasoline is less dense than water. b. 1 kg of gasoline because gasoline is more dense than water. c. 1 kg of water because water is more dense than gasoline. d. 1 kg of water because water is less dense than gasoline.
a. 1 kg of gasoline because gasoline is less dense than water. The water sinks because it's more dense. More dense means more compact, so gasoline takes up more space.
The onset of turbulent flow happens for a Reynolds number of about a. 2300 b. 0 c. Infinity d. 5000
a. 2300
Waterproof watches have a maximum depth to which they can safely be taken while swimming. Why? a. Deeper than that depth the water pressure is so great it might damage the watch. b. Deeper than that depth the air pressure inside the watch might cause the watch to burst. c. Because taking it to too great a depth would void the warranty on the watch. d. Deeper than that depth the air pressure is so great it might damage the watch.
a. Deeper than that depth the water pressure is so great it might damage the watch.
A water-skier skims along the surface of a lake. What types of forces is the water exerting on the skier, and what is the effect of these forces? a. Drag forces slow the skier, and lift forces hold the skier up. b. The Magnus force slows the skier, and lift forces hold the skier up. c. Drag forces slow the skier, and the Magnus force holds the skier up. d. The skis are streamlined, so lift forces hold the skier up.
a. Drag forces slow the skier, and lift forces hold the skier up.
Pedestrians on the surface of a windswept bridge don't feel the full intensity of the wind because the air is moving relatively slowly near the bridge's surface. Explain this effect in terms of a boundary layer. a. The air just above the bridge is kept from moving by viscous forces, forming a boundary layer. b. The air's Reynold's number is decreased by the boundary layer of air near the bridge. c. The air's Reynold's number is increased by the boundary layer of air near the bridge. d. The air just above the ground is kept from moving by friction, forming a boundary layer.
a. The air just above the bridge is kept from moving by viscous forces, forming a boundary layer. Viscous forces act like friction of the air with itself.
You have just set up a weather station for your daughter to observe wind speeds at home. You had to move it up from the ground because when it was too close to the ground the wind speed readings are all too small. This is because a. The boundary layer of a moving fluid moves slower than at other points farther into the fluid. b. Someone kept stepping on the wind speed gauge. c. The air near the ground is too dense to move well. d. The ground is hot so air movement there is always upward, never sideways.
a. The boundary layer of a moving fluid moves slower than at other points farther into the fluid.
Oil and vinegar salad dressing settles with the oil floating on top of the vinegar. Explain this phenomenon in terms of density. a. The oil is less dense than the vinegar. b. The liquids can be mixed if you shake the salad dressing vigorously. c. The oil is more dense than the vinegar. d. The oil is filled with air.
a. The oil is less dense than the vinegar. A less-dense liquid will float on top of a more-dense liquid.
You have two golf balls that differ only in their surfaces. One has dimples, while the other is smooth. Which ball has a greater pressure difference between the leading and trailing edges? a. The pressure difference is greater for the smooth ball. b. The pressures are exactly the same. c. there is no leading or trailing pressures. d. The pressure difference is greater for the dimpled ball.
a. The pressure difference is greater for the smooth ball.
Each time you breathe in, air accelerates toward your nose and lungs. How does the pressure in your lungs compare with that in the surrounding air as you breathe in? a. The pressure in your lungs is less than that of the surrounding air. b. The pressure in your lungs is equal to that of the surrounding air. c. There is no specific relationship between the pressure in your lungs and the pressure of the surrounding air. d. The pressure in your lungs is greater than that of the surrounding air.
a. The pressure in your lungs is less than that of the surrounding air. Air moves from higher pressure to lower pressure.
Racing bicycles often have smooth, disk-shaped covers over the spokes of their wheels. Why would these thin wire spokes be a problem for a fast-moving bicycle? a. They would create turbulence and increase drag. b. They would increase the turbulent drag. c. They would create more laminar flow. d. They would decrease the Reynolds number of the air flow
a. They would create turbulence and increase drag. The smooth cover encourages laminar flow over the wheel.
If you start two identical paper boats from the same point, you can make them follow the same path down a quiet stream. Why can't you do the same on a brook that contains eddies and vortices? a. Turbulent water flows in unpredictacle directions. b. The brook with eddies and vortices has laminar flow. c. Actually you can, you just have to be very careful.
a. Turbulent water flows in unpredictacle directions. Eddies and vortices mean turbulence is present.
When a fish is floating motionless below the surface of a lake, what is the amount and direction of the force the water is exerting on it? a. Upward, equal to the weight of the fish. b. Downward, less than the weight of the fish. c. Upward, greater than the weight of the fish. d. The water does not exert any force on the fish.
a. Upward, equal to the weight of the fish. The buoyant force from the water exactly balances the weight of the fish.
An automobile will float on water as long as it doesn't allow water to leak inside. In terms of density, why does admitting water cause the automobile to sink? a. Water is much denser than air, so replacing the air inside the car with water increases the car's average density. b. Water is denser than air. c. Removing the air in the car decreases the buoyant force on the car. d. The water makes the car heavier.
a. Water is much denser than air, so replacing the air inside the car with water increases the car's average density. When the car's average density exceeds that of water, it will sink.
The top surface of a calm, smoothly flowing stream is always at atmospheric pressure. As water in this stream runs into a tree stump and slows almost to a stop, the water's top surface a. shifts upward slightly above the normal stream level. b. stays at the same height and does not begin to rotate. c. stays at the same height but begins to rotate clockwise as viewed from above. d. shifts downward slightly below the normal stream level.
a. shifts upward slightly above the normal stream level.
To set the world land speed record and travel faster than the speed of sound, the Thrust SSC vehicle used two jet engines that produced about a 250,000 horsepower. The principal reason why this car needed so much power to travel so fast is that a. the pressure drag on a car increases dramatically as the car's speed increases. b. Newton's second law requires a very fast moving object to have a very large acceleration and thus a very large force. c. a car's momentum is proportional to its power, so reaching very high momentum requires very high power. d. the force of the car's momentum was enormous and the jet engines were needed to supply that force.
a. the pressure drag on a car increases dramatically as the car's speed increases.
The reason fast-moving water makes noise is a. turbulence. b. vortices. c. chaos. d. laminar flow
a. turbulence.
Why will a rolled - up ball of aluminum foil float in water but solid aluminum will sink? a. It won't - the ball will sink. b. Due to the air inside, the average density of the ball is lower than water. c. Aluminum is less dense than water anyway. d. Water cannot get in to equalize the pressure.
b. Due to the air inside, the average density of the ball is lower than water.
A favorite college prank involves simultaneously flushing several toilets while someone is in the shower. The cold water pressure to the shower drops and the shower becomes very hot. Why does the cold water pressure suddenly drop? a.The cold water is diverted from the shower to the toilets. b. Flushing makes the water in the pipes flow faster, dropping the pressure. c. Actually, the flushing increases the hot water pressure rather than lowering the cold water pressure. d. Flushing increases the water pressure at the toilets, lowering the pressure at the shower.
b. Flushing makes the water in the pipes flow faster, dropping the pressure. The faster a fluid moves, the lower the pressure.
When someone pulls a fire alarm in a skyscraper, pumps increase the water pressure in the section of the building nearest that alarm box. How does this pressure change assist firefighters who must battle the blaze? a. Greater pressure makes the water come out harder. b. Greater water pressure means the water emerges from the hoses faster, so it can spray farther. c. Greater pressure means more water comes out. d. Greater pressure means the water arrives sooner.
b. Greater water pressure means the water emerges from the hoses faster, so it can spray farther. Bernoulli's Equation in action.
Some fish move extremely slowly, and it's hard to tell whether they are even alive. However, if a fish is floating at a middle height in your aquarium and not at the top or bottom of the water, you can be pretty certain that it's alive. Why? a. Dead fish generally float to the top of the water. b. If the fish is floating at a middle height, it must be be regulating its density to be equal to the density of the water, which a dead fish couldn't do. c. Live fish can control their position in the water. d. If it's in the middle it must be swimming, no matter how slowly.
b. If the fish is floating at a middle height, it must be be regulating its density to be equal to the density of the water, which a dead fish couldn't do. The chances of a dead fish having exactly the same density as water are pretty small.
A helium-filled balloon floats in air. What will happen to an air-filled balloon in helium? Why? a. It will sink because helium is denser than air. b. It will sink because air is denser than helium. c. It will neither rise nor sink because air and helium are both gases. d. It will rise because helium is less dense than air.
b. It will sink because air is denser than helium.
You use your breath to inflate a large rubber tube and then ride down a snowy hill on it. After a few minutes in the snow the tube is underinflated. What happened to the air? a. It got cold. b. Its pressure decreased. c. It leaked out of the tube. d. The moisture in the air (from your breath) froze out.
b. Its pressure decreased. Lower temperature means lower pressure.
Why does hot maple syrup pour more easily than cold maple syrup? a. Its Reynolds number decreases at higher temperatures. b. Its viscosity is lower at higher temperatures. c. Its viscosity is higher at higher temperatures. d. Its Reynolds number increases at higher temperatures.
b. Its viscosity is lower at higher temperatures. Lower viscosity means faster flow, according to Poisseuille's Law.
A skillful volleyball player can serve the ball so that it barely spins at all. The ball dithers slightly from side to side as it flies over the net and is hard to return. What causes the ball to accelerate sideways? a. Drag forces caused by irregular air flow around the seams of the volleyball. b. Lift forces caused by irregular air flow around the seams of the volleyball. c. Wake deflection force caused by irregular air flow around the seams of the volleyball. d. Magnus force caused by irregular air flow around the seams of the volleyball.
b. Lift forces caused by irregular air flow around the seams of the volleyball. This is similar to a knuckleball in baseball, which also does not spin.
When a car is stopped, its flexible radio antenna points straight up. But when the car is moving rapidly down a highway, the antenna arcs toward the rear of the car. What force is bending the antenna? a. Laminar drag. b. Pressure drag. c. Turbulent drag. d. Viscous drag.
b. Pressure drag. The air flow around the antenna is turbulent, and pressure drag dominates in that case.
Why do flyswatters have many holes in them? a. The holes decrease the Reynolds number. b. The holes cause the boundary layer to become turbulent. c. The holes encourage laminar flow trhough the flyswatter. d. The holes decrease the turbulence.
b. The holes cause the boundary layer to become turbulent. This drastically decreases pressure drag.
Suppose you are ill and have to go to the hospital for shot. When the nurse points the fluid - filled syringe skyward to clear the air out of it, he presses the plunger down but no fluid comes out because the needle is plugged. When the plunger is pressed down and no fluid is moving, a. The pressure of the fluid in the needle is much more than in the larger syringe. b. The pressure of the fluid in the needle and much larger syringe are the same. c. The pressure of the fluid everywhere is zero. d. The pressure of the fluid in the needed is much less than in the larger syringe
b. The pressure of the fluid in the needle and much larger syringe are the same.
Some clear toys contain two colored liquids. No matter how you tilt one of those toys, one liquid remains above the other. What keeps the upper liquid above the lower liquid? a. The liquids can be mixed if you shake the toy vigorously. b. The upper liquid is less dense than the lower liquid. c. The upper liquid is filled with air. d. The upper liquid is more dense than the lower liquid.
b. The upper liquid is less dense than the lower liquid. A less-dense liquid will float on top of a more-dense liquid.
Many grocery stores display frozen foods in bins that are open at the top. Why doesn't the warm room air enter the bins and melt the food? a. Warm air does enter the bins, but it's not warm enough to melt the food. b. The warm air is blocked from the food by the cold air above the food. c. The warm air does enter the bins, but the refrigeration unit keeps the air cold enough to keep the food cold. d. Fans keep the warm air away.
b. The warm air is blocked from the food by the cold air above the food. This is true because cold air is denser than warm air and so stays close to the food.
In 1971, astronaut Alan Shepard hit a golf ball on the moon. How did the absence of air affect the ball's flight? a. There was no significant difference, as a golf ball is designed to have no drag. b. There was zero drag on the ball, only the moon's gravity. c. The absence of air makes the ball go farther. d. Not certain, as it would depend whether the golf ball had dimples or not.
b. There was zero drag on the ball, only the moon's gravity. The ball would travel quite a bit farther than on Earth.
Why are failures in dams more likely to occur closer to the bottom of the dam? a. Water is considerably more dense at the bottom. b. Water pressure is higher at the bottom. c. The temperature is higher at the bottom. d. Water weighs more at the bottom.
b. Water pressure is higher at the bottom.
For your high school science project you are able to get community support and terraform Mars, so that liquid water could exist on its surface. Suppose you have two cans of soda - one barely floats and one barely sinks in fresh water on Earth. Taking them to Mars, with the gravitational acceleration being 1/3 its value on earth, a. Both objects will now float because they are lighter. b. We can't say anything until we know if the water on Mars is freshwater or not. c. The buoyant behavior of the two objects will be the same. d. Both objects will sink because the water is lighter.
b. We can't say anything until we know if the water on Mars is freshwater or not.
As the Reynolds number increases, a. flow is becoming more laminar. b. flow is going from being viscous dominated to inertia dominated and therefore turbulent. c. flow is speeding up. d. flow is slowing down.
b. flow is going from being viscous dominated to inertia dominated and therefore turbulent.
When a Frisbee is flying horizontally through the air, the speed of the air flowing over the Frisbee's top is a. lower than the speed of the air beneath it and the pressure on top of the Frisbee is less than the pressure beneath it. b. higher than the speed of the air beneath it and the pressure on top of the Frisbee is less than the pressure beneath it. c. higher than the speed of the air beneath it and the pressure on top of the Frisbee is greater than the pressure beneath it. d. lower than the speed of the air beneath it and the pressure on top of the Frisbee is greater than the pressure beneath it.
b. higher than the speed of the air beneath it and the pressure on top of the Frisbee is less than the pressure beneath it.
The pressure in a water pipe is always lower in regions where the water moves faster only when a. anything other than water is in the pipe b. the pipe is level. c. the pipe increases in altitude towards the faster fluid end d. the pipe is made of plastic
b. the pipe is level.
When driving down a level smooth road, your car tires flatten at the bottom and they nicely support the weight of your car. However when you run over a small pointed rock the tire is punctured and fails. The rock is able to puncture the tire because a. the car has much more gravitational potential energy when on the rock than when on the flat road and this gravitational potential energy becomes pressure potential energy in the tire. b. the small surface area of the rock times the pressure in the tire is not enough force to support the car. Thus, the tire fails. c. the car has much more kinetic energy when on the rock than when on the flat road and this kinetic energy becomes potential energy in the tire. d. when the car is on the rock almost all its weight is on the tire over the rock.
b. the small surface area of the rock times the pressure in the tire is not enough force to support the car. Thus, the tire fails.
Water weighs about 10 N per liter on Earth. A 4.0 liter ball is pushed underwater on the space shuttle, where gravity was 1/10 that on Earth. What is the buoyant force on the ball? a. 1N b. 10 N c. 4 N d. 40 N
c. 4 N
The brake system in most cars makes use of a hydraulic system. This system consists of a fluid filled tube connected at each end to a piston. Assume that the piston attached to the brake pedal has a cross Section: al area of one half a square inch and the piston attached to the brake pad has a cross Section: area of two square inches. When you apply a force of 10 pounds to the piston attached to the brake pedal, the force at the brake pad will be, a. 20 pounds. b. 5 pounds. c. 40 pounds. d. 10 pounds.
c. 40 pounds.
How does pushing on the plunger of a syringe cause medicine to flow into a patient through a hollow hypodermic needle? a. Pushing the plunger decreases the gravitational potential energy of the fluid as the depth of the fluid decreases, so the kinetic energy of the fluid increases (the fluid starts moving). b. The air pressure increases? c. Bernoulli's Equation: pressure on the fluid converts to kinetic energy (motion) of the fluid. d. The force on the fluid pushes it out of the syringe.
c. Bernoulli's Equation: pressure on the fluid converts to kinetic energy (motion) of the fluid. The increased pressure is on one side of the equation and the increased kinetic energy is on the other.
Gravity creates a. Uniform pressure in fluids b. Lack of pressure on the top of all fluids c. Pressure gradients in fluids d. Constant motion in fluids
c. Pressure gradients in fluids
Explain why a parachute slows your descent when you leap out of an airplane. a. The air flow around the parachute is turbulent with a large turbulent wake, leading to huge viscous drag forces and a relatively small terminal velocity. b. The air flow around the parachute is turbulent with a small turbulent wake, leading to huge viscous drag forces and a relatively small terminal velocity. c. The air flow around the parachute is turbulent with a large turbulent wake, leading to huge pressure drag forces and a relatively small terminal velocity. d. The air flow around the parachute is turbulent with a small turbulent wake, leading to huge pressure drag forces and a relatively small terminal velocity.
c. The air flow around the parachute is turbulent with a large turbulent wake, leading to huge pressure drag forces and a relatively small terminal velocity. The Reynolds number here is between 2000 - 100,000.
You seal a rigid container that is half full of hot food and put it in the refrigerator. Why is the container's lid bowed inward when you look at it later? a. The weight of the lid makes it bow inward. b. The air gets more dense as it gets colder. c. The air pressure of the air outside the container pushes the lid in. d. The hot food shrinks as it cools.
c. The air pressure of the air outside the container pushes the lid in. The air inside the container cools in the refrigerator, lowering its pressure. The greater pressure outside pushes the lid inward.
Why must tall dams be so much thicker at their bases than at their tops? a. The pressure is greater at the bottom due to greater kinetic energy per volume at the top. b. The pressure is greater at the bottom due to greater pressure at the top. c. The greater the depth of the water the greater the pressure pushing on the wall of the dam. d. A tall dam needs a lot of structural support.
c. The greater the depth of the water the greater the pressure pushing on the wall of the dam. At the base of the dam the water is much deeper than at the top, so the pressure is greater.
Why does a relatively modest narrowing of the coronary arteries, the blood vessels supplying blood to the heart, cause a dramatic drop in the amount of blood flowing through them? a. The rate at which blood flows is proportional to the diameter of the blood vessel to the third power. b. The rate at which blood flows is inversely proportional to the diameter of the blood vessel. c. The rate at which blood flows is proportional to the diameter of the blood vessel to the fourth power. d. The rate at which blood flows is proportional to the diameter of the blood vessel squared.
c. The rate at which blood flows is proportional to the diameter of the blood vessel to the fourth power. Blood is a viscous fluid, and Poiseuille's Law governs the flow of viscous fluids.
Why is it so difficult to squeeze ketchup through a very small hole in its packet? a. The rate at which ketchup flows is proportional to the diameter of the hole to the third power. b. The rate at which ketchup flows is inversely proportional to the diameter of the hole. c. The rate at which ketchup flows is proportional to the diameter of the hole to the fourth power. d. The rate at which ketchup flows is proportional to the diameter of the hole squared.
c. The rate at which ketchup flows is proportional to the diameter of the hole to the fourth power. Ketchup is a viscous fluid, and Poiseuille's Law governs the flow of viscous fluids.
When you mix milk or sugar into your coffee, you should move the spoon quickly enough to produce turbulent flow around the spoon. Why does this turbulence aid mixing? a. Mixing is more efficient in a turbulent flow than a laminar flow. b. The turbulence results from a small Reynolds number. c. The turbulence causes the coffee to move quickly in random directions, aiding mixing. d. The turbulence results from a large Reynolds number.
c. The turbulence causes the coffee to move quickly in random directions, aiding mixing.
A log is much heavier than a stick, yet both of them float in water. Why doesn't the log's greater weight cause it to sink? a. The water weighs more than the log. b. Wood always floats. c. The upward buoyant force on the log is greater than its weight. d. The upward buoyant force on the log is greater than the upward buoyant force on the stick.
c. The upward buoyant force on the log is greater than its weight. This is because wood is less dense than water.
For an object that is neutrally buoyant in a fluid, a. The weight of fluid displaced is less than its weight. b. The weight of the fluid displaced is greater than the object's weight. c. The weight of the fluid displaced equals the object's weight. d. The object has zero weight.
c. The weight of the fluid displaced equals the object's weight.
When you swing a stick slowly through the air, it's silent, but when you swing it quickly, you hear a "whoosh" sound. What behavior of the air is creating that noise? a. The Reynolds number of the air flow is low when the stick moves rapidly. b. There is a boundary layer of air near the surface of the stick. c. There is turbulence behind the rapidly-moving stick. d. There is laminar flow around the rapidly-moving stick.
c. There is turbulence behind the rapidly-moving stick. Turbulent means rapid, unpredictable motion, resulting in the sound.
Cities have to use water towers to supply water to because a. Water pressure at the top of the tower is transmitted through the water pipes. b. The water tower has a vault of air that is pressurized. c. Water pressure at the bottom of the tower is much higher than at the top. d. Water moves fastest at the bottom of the water tower and this speed is transmitted uniformly throughout all water pipes below.
c. Water pressure at the bottom of the tower is much higher than at the top.
An electric valve controls the water for the lawn sprinklers in your backyard. Why do the pipes in your home shake whenever this valve suddenly stops the water but not when the valve suddenly starts the water? a. The shaking is from the vibration of the valve slamming shut. b. Any shaking is absorbed by the flowing water. c. When the valve closes the water flow stops suddenly, resulting in a water hammer, but when the valve opens the flow does not instantly reach full speed. d. The pipes do shake when the flow starts, but you're less likely to notice it.
c. When the valve closes the water flow stops suddenly, resulting in a water hammer, but when the valve opens the flow does not instantly reach full speed. The sudden stop causes the shaking.
If you put your hand out the window of a moving car, so that your palm is mostly forward but tipped slightly downward, the force on your hand will be both backward and upward. How is the airstream exerting an upward force on your hand? a. Drag forces on your hand drag it upward. b. The air pressure above your hand is higher than the air pressure below. c. Your hand pushes the airflow downward, and as a reaction the airflow pushes your hand upward. d. The airstream is generating lift on your hand.
c. Your hand pushes the airflow downward, and as a reaction the airflow pushes your hand upward. This is the Newtonian view of how lift works in this case.
A block of hardwood is floating easily on the surface of a lake. As a storm approaches, the density and pressure of the air above the lake begin to decrease. As a result of this decrease in air pressure and density, the block of wood a. moves upward slightly and floats higher in the water. b. continues to float just as it did before. c. moves downward slightly and floats lower in the water. d. sinks to the bottom of the lake.
c. moves downward slightly and floats lower in the water.
Water weighs about 10 N per liter. A 4.0 liter ball is pushed underwater. What is the buoyant force on the ball? a. 20 N b. 4.0 liters c. 10 N d. 40 N
d. 40 N
You are in a hot air balloon and are hovering in the air so that the atmospheric pressure remains constant. At a temperature of 300 K your balloon holds 5x106 liter of air. The sun comes out and the temperature rises to 330 K. What is the new volume of the balloon? You may assume that no air can exit or enter the balloon. a. Not enough information is given to determine. b. 4.5 ×106 liter c. 5 × 106 liter d. 5.5 × 106 liter
d. 5.5 × 106 liter
The diameter of a pipe is tripled while the pressure difference across the pipe remains the same. The volume flow rate of the pipe increases by a factor of a. 3 b. 9 c. 27 d. 81
d. 81
Why does an airplane have a "flight ceiling," a maximum altitude above which it can't obtain enough lift to balance the downward force of gravity? a. Above that altitude there isn't enough air to generate sufficient lift. b. Above that altitude the air is too cold to generate sufficient lift. c. Above that altitude the air pressure is too low to generate sufficient lift. d. Above that altitude the air density is too low to generate sufficient lift.
d. Above that altitude the air density is too low to generate sufficient lift.
If you put your hand out the window of a moving car, so that your palm is pointing directly forward, the force on your hand is directly backward. Explain why the two halves of the airstream, passing over and under your hand, don't produce an overall up or down force on your hand. a. There is a downward force due to gravity. b. There will be an up or down force if you tilt your hand. c. The lift forces are overwhelmed by the drag forces. d. Any lift forces cancel each other out because of a symmetric air flow.
d. Any lift forces cancel each other out because of a symmetric air flow. If your hand were tilted this would not be the case.
A popular drink is composed by pouring several types of beverage (one on top of the other) in order to get a layering effect. In what order should the individual beverages be poured into the glass so that your drink is stable? a. Not enough information is given b. Most dense on the top and bottom to hold the least dense fluids in the middle. c. Least dense first and then in order of increasing density. d. Most dense first and then in order of decreasing density.
d. Most dense first and then in order of decreasing density.
If you seal a soft plastic bottle or juice container while hiking high in the mountains and then return to the valley, the container will be dented inward. What causes this compression? a. The mountain air inside is colder and so it is less dense. b. The air inside the container is less dense. c. The air inside the container takes up less volume once the container dents inward. d. The air inside the container is at a lower pressure than the air outside
d. The air inside the container is at a lower pressure than the air outside The higher pressure causes the container to collapse until the air inside is at the same pressure as the air outside.
Many jars have dimples in their lids that pop up when you open the jar. What holds the dimple down while the jar is sealed, and why does it pop up when the jar is opened? a. The air inside the jar is at higher pressure than the air outside, which holds the dimple down. When the pressure equalizes, the dimple pops back to its normal position. b. The air inside is more dense than the air outside. When the lid is opened, the densities equalize, and the dimple pops back to its normal position. c. The air inside is less dense than the air outside. When the lid is opened, the densities equalize, and the dimple pops back to its normal position. d. The air outside is at higher pressure than the air inside the jar, which holds the dimple down. When the pressure equalizes, the dimple pops back to its normal position.
d. The air outside is at higher pressure than the air inside the jar, which holds the dimple down. When the pressure equalizes, the dimple pops back to its normal position. The dimple's normal position is out. Only the greater pressure from outside holds it down.
If you place a hot, wet cup upside down on a smooth counter for a few seconds, you may find it difficult to lift up again. What is holding that cup down on the counter? a. The weight of the cup. b. The liquid on the rim of the cup forms a seal with the counter. c. The liquid on the rim of the cup sticks to the counter. d. The air pressure of the air outside the cup
d. The air pressure of the air outside the cup The air inside the cup cools through its contact with the counter, lowering its pressure. The greater pressure outside holds the cup to the counter.
A poorly designed household fan stalls, making it inefficient at moving air. Describe the airflow through the fan when its blades stall. a. The airflow is laminar rather than turbulent. b. The airflow is shedding vortices. c. The airflow is generating shock waves. d. The airflow is turbulent rather than laminar.
d. The airflow is turbulent rather than laminar. This leads to large amounts of drag. The fan becomes an air mixer rather than an air mover.
When a plane enters a steep dive, the air rushes toward it from below. If the pilot pulls up suddenly from such a dive, the wings may abruptly stall, even though the plane is oriented horizontally. Explain why the wings stall. a. The airflow is too slow to maintain lift. b. The airflow suddenly becomes turbulent. c. The angle of attack becomes too small. d. The angle of attack becomes too large.
d. The angle of attack becomes too large. The airflow is not horizontal in this case, and angle of attack is the angle between the direction of the airflow and the angle of the wing.
You have two golf balls that differ only in their surfaces. One has dimples on it while the other is smooth. If you drop these two balls simultaneously from a tall tower, which one will hit the ground first? a. Both will hit simultaneously. b. The smooth ball. c. Whichever ball is heavier. d. The dimpled ball.
d. The dimpled ball.
Ice tea is often dispensed from a large jug with a faucet near the bottom. Why does the speed of tea flowing out of the faucet decrease as the jug empties? a. Pressure decreases as the height of the tea decreases. b. As the container empties the air inside expands to fill the volume of the container, creating a suction effect which slows the tea coming out. c. There is less tea, so it comes out slower. d. The gravitational potential energy due to the depth of the tea decreases as the height of the tea decreases.
d. The gravitational potential energy due to the depth of the tea decreases as the height of the tea decreases. Decreased potential energy on one side of Bernoulli's Equation means decreased speed on the other.
You can inflate a plastic bag by holding it up so that it catches the wind. Use Bernoulli's equation to explain this effect. a. The air blows up the bag. b. The potential energy of the moving air converts into greater air pressure inside the bag, which inflates the bag. c. The pressure of the moving air converts into greater air pressure inside the bag, which inflates the bag. d. The kinetic energy of the moving air converts into greater air pressure inside the bag, which inflates the bag.
d. The kinetic energy of the moving air converts into greater air pressure inside the bag, which inflates the bag.
If you drop a full can of applesauce and it strikes a cement floor squarely with its flat bottom, what happens to the pressures at the top and bottom of the can? a. The pressure at the top is higher than the pressure at the bottom. b. There is no particular relationship between the pressure at the top and at the bottom. c. The pressure at the top is equal to the pressure at the bottom. d. The pressure at the top is lower than the pressure at the bottom.
d. The pressure at the top is lower than the pressure at the bottom. Applesauce is a viscous fluid. A pressure difference between the two ends will cause a flow from one end to the other.
If you ride your bicycle directly behind a large truck, you will find that you don't have to pedal very hard to keep moving forward. Why? a. The air flow around the truck has a large Reynolds number. b. The air flow around the truck has a small Reynolds number. c. The laminar wake behind the truck shields objects in that wake from the air flow around the truck. d. The turbulent wake behind the truck shields objects in that wake from the air flow around the truck.
d. The turbulent wake behind the truck shields objects in that wake from the air flow around the truck. Effectively, the air right behind the truck travels with the truck.
If you let a stream of water from a faucet flow rapidly over the curved bottom of a spoon, the spoon will be drawn into the stream. Explain this effect. a. The drag forces on the spoon drag it into the stream. b. The spoon is perfectly streamlined and this causes a lift force. c. The water pushing against the spoon pushes it into the stream. d. The water flowing over the spoon moves faster and so is at lower pressure than the water flowing on the other side.
d. The water flowing over the spoon moves faster and so is at lower pressure than the water flowing on the other side. This is similar to the lift on an airplane wing.
If you try to fill a bucket by holding it in a waterfall, you will find the bucket pushed downward with enormous force. How does the falling water exert such a huge downward force on the bucket? a. The water has a lot of inertia. b. The water has a lot of momentum. c. The falling water pushes on the bucket. d. The water goes from high speed and low pressure to low speed and high pressure when it hits the bucket.
d. The water goes from high speed and low pressure to low speed and high pressure when it hits the bucket.
For an object that sinks in a fluid, a. The weight of the fluid displaced is greater than the object's weight. b. The weight of the object becomes more than in air. c. The weight of the fluid displaced equals the object's weight. d. The weight of fluid displaced is less than its weight.
d. The weight of fluid displaced is less than its weight.
Suppose you had a very long straw that could reach from a cup of water on the ground level to the top of a very tall building. When you suck on the straw in order to bring water up, a. You could bring the water up to only a certain height in the straw because after it will flash freeze in the cup. b. Water is too thick to be pulled up in the straw by more than a few inches. c. You could drink the water at any height with no problem d. You could bring the water up to only a certain height in the straw because the atmosphere pushes down on the surface of the water by a given amount
d. You could bring the water up to only a certain height in the straw because the atmosphere pushes down on the surface of the water by a given amount
A curve ball's path bends to the right as it flies toward home plate because it is experiencing an aerodynamic force to its right. One reason why the ball is experiencing this aerodynamic force is that the ball is spinning and that spin a. exerts a torque on the ball that causes its angular momentum to shift toward the left. b. causes the air to flow more rapidly around the left side of the ball than around the right side of the ball. c. exerts a torque on the ball that causes its angular momentum to shift toward the right. d. causes the air to flow more rapidly around the right side of the ball than around the left side of the ball.
d. causes the air to flow more rapidly around the right side of the ball than around the left side of the ball.
You are floating along in a hot air balloon. You look up and notice that the bottom of the balloon is open. Neglecting any diffusion of molecules, hot air remains inside the balloon despite this opening because a. the propane burner located below the opening keeps pushing the hot air back into the balloon. b. hot air has a lower pressure than cold air, so hot air is drawn into the balloon by the partial vacuum inside it. c. hot air has more inertia than cold air and doesn't accelerate easily. d. convection naturally would make hot air rise, so it has no opening through which to escape.
d. convection naturally would make hot air rise, so it has no opening through which to escape.
Flowing honey is less likely to become turbulent than flowing water because a. honey's large density favors laminar flow. b. water's large viscosity favors turbulent flow. c. water's large pressure favors turbulent flow. d. honey's large viscosity favors laminar flow.
d. honey's large viscosity favors laminar flow.
You are trying to deliver water to a sink in the tree house in your backyard. You run an old hose from the spigot behind your home, across your yard, and up the tree to a sink inside the tree house. You let water fill the hose all the way to the tree house sink and then leave the hose pressurized overnight, with no water flowing in it. Unfortunately, the hose cannot tolerate high pressure anymore and it springs a leak around midnight. By morning your whole backyard is a swamp. The most likely site for the leak is a. at the spigot—the first point on the hose. b. on the way up the tree—the most vertical portion of the hose. c. at the sink—the highest point on the hose. d. on the ground—the lowest point on the hose.
d. on the ground—the lowest point on the hose.
As air flows through the horizontal ductwork in a warehouse, it passes through a fan inside the duct and the air's total energy increases. Since the air's speed doesn't change as the result of going through the fan, you know that the air's a. kinetic energy has decreased but its pressure has remained the same. b. kinetic energy has increased but its pressure has remained the same. c. pressure has decreased but its kinetic energy has remained the same. d. pressure has increased but its kinetic energy has remained the same.
d. pressure has increased but its kinetic energy has remained the same
The pressure in a water pipe may not necessarily be lower in regions where the water moves faster when a. the pipe is level. b. the pipe is in free fall. c. the pipe is in zero gravity. d. the pipe is not level
d. the pipe is not level
If the plumbing in your dorm carried honey instead of water, filling a cup to brush your teeth could take awhile. If the faucet takes 9 s to fill a cup with water, how long will it take to fill your cup with honey, assuming all the pressures and pipes remain unchanged? Answer in s (seconds).
t = 9000000 s
To clean the outside of your house you rent a small high-pressure water sprayer. The sprayer's pump delivers slow-moving water at a pressure of 5,000,000.0 Pa (about 50.0 atmospheres). How fast can this water move if all of its pressure potential energy becomes kinetic energy as it flows through the nozzle of the sprayer? Answer in m/s. Density of water = 1000 kg/m³
v = 100 m/s 1. PPE = 5,000,000 2. PPE = KE 3. KE = 1/2(density)(velocity)² 5000000 = 1/2(1000)v² 5000000 = 500v² 10000 = v² 100 = v
