Conceptual Physics: Chapter 14: Gases
When a steadily flowing gas flows from a larger-diameter pipe to a smaller-diameter pipe, what happens to (a) its speed (b) its pressure, and (c) the spacing between its streamlines?e
(a) speed increases so that the same quantity of gas can move through the pipe in the same time. (b) pressure decreases (Bernoulli's principle). (c) the spacing btw the streamlines decreases, because the same number of streamlines fit in a smaller area.
You ordinarily pour water from a full glass into an empty glass simply by placing the full glass above the empty glass and tipping. Have you every poured air from one glass into another? The procedure is similar. Lower two glasses in water, mouths downward. Let one fill with water by tilting its mouth upward. Then hold the water filled glass mouth downward above the air-filled glass. Slowly tilt the lower glass and let air escape, filling the upper glass. You will be pouring air from one glass into another!
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Does the air exert a buoyant force on all objects in air or only on objects such as balloons that are very light for their size?
A BF exists for all objects that displace fluid.
If the number of gas atoms in a container is doubled, the pressure of the gas doubles (assuming constant temperature and volume). Explain this pressure increase in terms of the molecular motion of the gas.
A moving molecule encountering a surface imparts force to the surface. The greater the number of impacts on a given-size surface, the greater the pressure.
Suppose that the pup shown in figure 14. 9 operated with a perfect vacuum. From how deep a well could water be pumped?
A perfect vacuum pump could pump water no higher than 10.3 m. This is because the atmospheric pressure that pushes the water up the tube weighs as much as 10.3 vertical meters of water of the same cross-sectional area.
Wharves are made with pilings that permit the free passage of water. Why would a solid-walled wharf be disadvantageous to ships attempting to pull alongside?
A solid-walled wharf is disadvantageous to ships pulling alongside because water currents are constrained and speed up between the sip and the wharf. This results in a reduced water pressure, and the normal pressure on the other side of the ship then forces the ship against the wharf. The pilings avoid this mishap by allowing the freer passage of water between the wharf and the ship.
Why is it easier to throw a curve with a tennis ball than a baseball?
A tennis ball has about the same size as a baseball, but much less mass. Less mass means less inertia, and more acceleration for the same force. A ping-pong ball provides a more obvious curve due to spinning because of its low mass.
The "pump" in a vacuum cleaner is merely a high-speed fan. Would a vacuum cleaner pick up dust from a rug on the Moon? Explain.
A vacuum cleaner wouldn't work on the Moon. A vacuum cleaner operates on Earth because the atmospheric pressure pushes dust into the machine's region of reduced pressure. On the Moon there is no atmospheric pressure to push the dust anywhere.
Rank the volumes of air in the glass, from greatest to least, when it is held a. near the surface as shown. b. 1 m beneath the surface. c. 2 m beneath the surface.
ABC
Rank the buoyant forces supplied by the atmosphere on the following, from greatest to least: a. An elephant b. A helium-filled party balloon c. A skydiver at terminal velocity.
ACB
Why does the fire in a fireplace burn more briskly on a windy day?
According to Bernoulli's principle, the wind at the top of the chimney lowers the pressure there, producing a better "draw" in the fireplace below.
What change in pressure occurs in a party balloon that is squeezed to one-third its volume with no change in temperature?
According to Boyle's law, the pressure will increase to 3 times its original pressure.
What provides the lift to keep a Frisbee in flight?
Air moves faster over the spinning top of the frisbee and pressure against the top is reduced. A frisbee, like a wing, needs an "angle of attack" to ensure that the air flowing over it follows a longer path than the air flowing under it. So there is a difference in pressures against the top and bottom of the frisbee that produces an upward lift.
Why do airplanes normally take off facing the wind?
Air speed across the wing surfaces, necessary for flight is greater when facing the wind.
Why do you suppose that airplane windows are smaller than bus windows?
Airplane windows are small because the pressure difference between the inside and outside surfaces result in large net forces that are directly proportional to the window's surface area. (Larger windows would have to be proportionally thicker to withstand the greater net force - windows on underwater research vessels are similarly small.
How is an airplane able to fly upside down?
An airplane flies upside down by tilting its fuselage so that there is an angle of attack of the wing with oncoming air. (It does the same when flying right side up, but then, because the wings are designed for right-side-up flight, the tilt of the fuselage may not need to be as great.)
What is an ideal gas?
An ideal gas is one in which intermolecular forces and size of molecules can be neglected.
A steel tank filled with helium gas doesn't rise in air, but a balloon containing the same helium rises easily. Why?
An object rises in air only when buoyant force exceeds its weight. A steel tank of anything weighs more than the air it displaces, so it won't rise. Also, the helium is compressed in the tank, and wouldn't rise if the tank's weight were nil. A helium-filled balloon weighs less than the air it displaces and rises.
What is the approximate mass of a column of air 1 cm2 in area that extends from sea level to the upper atmosphere? What is the weight of this amount of air?
Aprroximate mass is 1 kg, with weight 10 N.
What happens to the pressure in water as it speeds up when it is ejected by the nozzle of a garden hose?
As speed of water increases, internal pressure within the water decreases.
Why is a soft, underinflated football at sea level much firmer than when it is taken to a high elevation in the mountains?
At higher altitude, less atmospheric pressure is exerted on the ball's exterior, making relative pressure within greater, resulting in a firmer ball.
Place a card over the top of a glass filled to the brim with water and invert it. Why does the card stay in place? Try it sideways.
Atmospheric pressure holds the card to the glass in any direction.
A balloon that weighs 1 N is suspended in air, drifting neither up nor down. (a) How much buoyant force acts on it? (b) What happens if the buoyant force decreases? (c) If it increases?
BF equals 1 N. If the BF decreases, the balloon descends. If BF increases the balloon ascends.
What physics principle underlies these three observations? When passing an oncoming truck on the highway, your car tends to sway toward the truck. The canvas roof of a convertible car bulges upward when the car is traveling at high speeds. The windows of older trains sometimes break when a high-speed train passes by on the next track.
Bernoulli's Principle. For the moving car the pressure will be less on the side of the car where the air is moving fastest - the side nearest the truck, resulting in the car's being pushed by the atmosphere towards the trick. inside the convertible, atmospheric pressure is greater than outside and the canvas rooftop is pushed upwards toward the region of less pressure. Similarly for train windows, where the interior air is at rest relative to the window and the air outside is in motion. Air pressure against the inner surface of the window is greater than the atmospheric pressure outside. When the diff. in pressures is great enough, the window is blown out.
Does Bernoulli's principle refer to changes in the internal pressure of a fluid or to pressures the fluid may exert on objects?
Bernoulli's principle is about internal pressures.
How does the pressure at the bottom of a 76-cm column of mercury in a barometer compare with the air pressure at the bottom of the atmosphere?
Both pressures are the same.
How does the weight of mercury in a barometer compare with the weight of an equal cross-section of air from sea level to the top of the atmosphere?
Both weights of the same.
Rank from most to least, the amounts of lift on the following airplane wings: a. Area 1000 m2 with an atmospheric pressure difference of 2.0 N/m2. b. Area 800 m2 with an atmospheric pressure difference of 2.4 N/m2 c. Area of 600 m2, with an atmospheric pressure difference of 3.8 N/m2.
CAB
By how much does the density of air increase when it is compressed to half its volume?
Density doubles when volume is halved.
Would it be slightly more difficult to draw soda through a straw at sea level or on top of a very high mountain? Explain.
Drinking through a straw is slightly more difficult atop a mountain. This is because the reduced atmospheric pressure is less effective in pushing soda up into the straw.
How does faster-moving air above an airplane wing affect the pressure on the wing?
Faster-moving air above the wing has reduced pressure.
How does faster-moving water between two ships affect water pressure against the sides of the ships?
Faster-moving water between the ships results in reduced pressure.
The weight of the atmosphere above 1 square meter of Earth's surface is about 100,000 N. Density, of course, decreases with altitude. But suppose the density of air were a constant 1.2 kg/m3. Calculate where the top of the atmosphere would be.
From P=F/A = (den x g x vol)/A = (den x g x A x h)/A = den x g x h; h = P/(den x g) = 100,000 N/m2/ 1/2 kg/m3 x 10 N/kg = 8300 m = 8.3 km
Why do airplanes extend wing flaps that increase the area and the angle of attack of the wing during takeoffs and landings? Why are these flaps pulled in when the airplane has reached cruising speed?
Greater wing area produces greater lift, important for low speeds where lift otherwise would be less. Flaps are pulled in to reduce area at cruising speed, where a smaller wing can provide lift equal to the weight of the aircraft.
How high would you have to go in the atmosphere for half of the mass of air to be below you?
Half of the atmosphere is below 5.6 kilometers.
Would a bottle of helium gas weigh more or less than an identical bottle filled with air at the same pressure? Than an identical bottle with air pumped out?
Helium is less dense than air, and will weigh less than an equal volume of air. A helium-filled bottle would weigh less than the air bottle (assuming they are filled to the same pressure). However, the helium filled bottle will weigh more than the empty bottle.
The pressure exerted against the ground by an elephant's weight distributed evenly over its four feet is less than 1 atmosphere. Discuss why it is that you'd be crushed beneath the food of an elephant ,while you're unharmed by the pressure of the atmosphere.
If an elephant steps on you the pressure that the elephant exerts is over and above the atmospheric pressure that already is exerted on you. It is the extra pressure the elephant's foot produces that crushes you. For example, if atmospheric pressure the size of the elephant's foot were somehow removed from a patch of your body, you would be in serious trouble. You would be soothed, however, if an elephant stepped onto this area!
If a liquid only half as dense as mercury were used in a barometer, how high would its level be on a day of normal atmospheric pressure?
If barometer liquid were half as dense as mercury, then to weight as much, a column twice as high would be required. A barometer using such liquid would therefore have to be twice the height of a standard mercury barometer, or about 152 cm instead of 76 cm.
Discuss which will register the greater weight: an empty flattened balloon or the same balloon filled with air. Defend your answer.
If the air pressure in the inflated balloon were equal to the outside air pressure, the extra weight of the air in the balloon would be canceled by an equal buoyant force and the scale reading would not change. But to keep a rubber balloon inflated, its air pressure inside has to be greater than outside air pressure. Then the extra weight is greater than the buoyant force and the scale will show a greater weight.
When boarding an airplane you bring a bag of chips (or any other item packaged in an airtight foil package) and, while you are in flight, you notice that the bag puffs up. Discuss why this happens.
If the item is sealed in an air-tight package at sea level, then the pressure in the package is about 1 atmosphere, Cabin pressure is reduced somewhat for high altitude flying, so the pressure in the package is greater than the surrounding pressure and the package therefore puffs outwards.
How will two dangling vertical sheets of paper move when you blow between them? Try it and see.
In accord with Bernoulli's principle, the sheets of paper will move together because air pressure between them is reduced, and be less than the air pressure on the outside surfaces.
Why would a water barometer have to be 13.6 times taller than a mercury barometer?
It would have to be taller because it's 1/13.6 as dense.
What can be produced when a plasma beam is directed into the field of a strong magnet?
Low pollution MHD power can be produced when a plasma beam is directed into the field of a magnet.
From how deep a container could mercury be drawn with a siphon?
Mercury can be drawn a maximum of 76 cm with a siphon. This is because 76 vertical cm of mercury exert the same pressure as a column of air that extends to the top of the atmosphere. Or looked at another way: water can be lifted 10.3 m by atmospheric pressure. Mercury is 13.6 times denser than water, so it can only be lifted 1/13.6 times as high as water.
Consider an airplane with a total wing surface of 100 square meters. At a certain speed the difference in air pressure below and above the winds is 4% of atmospheric pressure. Show that the lift of the airplane is 400,000 N.
N/A
Cite at least three examples of plasma in your daily environment.
Neon signs, fluorescent lamps, certain TV screens.
On a sensitive balance, weigh an empty, flat, thin plastic bag. Then weight the bag filled with air. Discuss whether or not the readings differ.
No, assuming the air is not compressed. The air filled bag is heavier, but buoyancy negates the extra weight and the reading is the same. The buoyant force equals the weight of the displaced air, which is the same as the weight of the air inside the bag (if the pressures are the same).
Why does a precision scale give different readings for the weight of an object in air and in a vacuum (remembering that weight is the force exerted against a supporting surface)? City an example in which this would be an important consideration.
Objects that displace air are buoyed up by a force equal to the weight of air displaced. Objects therefore weigh less in air than in a vacuum. For objects of low densities, like bags of compressed gasses, this can be important. For high-density objects like rocks and boulders the difference is usually negligible.
Why is it so difficult to breathe when snorkeling at a depth of 1 m and practically impossible at a 2-m depth? Why can't a diver simply breath through a hose that extends to the surface?
One's lungs, like an inflated balloon, are compressed when submerged in water, and the air within is compressed. Air will not of itself flow from a region of low pressure into a region of high pressure. The diaphragm in one's body reduces lung pressure to permit breathing, but this limit is strained when nearly 1 m below the water surface. This limit is exceeded at more than a depth of 1 m.
How does a plasma differ from a gas?
Particles in a gas are electrically neutral. In a plasma they're charged.
What happens to the air pressure inside a balloon when it is squeezed to half its volume at a constant temperature?
Pressure doubles when volume is halved.
What is the pressure at the bottom of the column of air referred to in the preceding question?
Pressure is 10 N/cm2.
What happens to the size of the air bubbles released by a diver as they rise?
Pressure of the water decreases and the bubbles expand.
It is said that a gas fills all the space available to it. Why, then, doesn't the atmosphere go off into space?
Some of the molecules in the Earth's atmosphere do go off into outer space - those like helium with speeds greater than escape speed. But the average speeds of molecules in the atmosphere are well below escape speed, so the atmosphere is held to Earth by Earth's gravity.
Why is there no atmosphere on the Moon?
There is no atmosphere on the Moon because the speed of a sizable fraction of gas molecules at ordinary temperatures exeeds lunar escape velocity (because of the moon's smaller gravity). Any appreciable amounts of gas have long leaked away, leaving the moon airless.
Two teams of eight horses each were unable to pull the Magdeburg hemispheres apart. Suppose that two teams of nine horses each could pull them apart. Then would one team of nine horses succeed if the other team were replaced with a strong tree?
To begin with, the two teams of horses used in the Magdeburg hemispheres demonstration were for showmanship and effect, for a single team and a strong tree would have provided the same force on the hemispheres. So if two teams of nine horses each could pull the hemispheres apart, a single team of nine horses could also, if a tree or some other strong object were used to hold the other end of the rope.
A mountain-climber friend with a mass of 80 kg ponders the idea of attaching a helium filled balloon to himself to effectively reduce his weight by 25% when he climbs. He wonders what the approximate size of such a balloon would be. Hearing of your physics skills, he asks you. Share with him your calculations that show the volume of the balloon to be about 17 m3 (slightly more than 3 m in diameter for a spherical balloon).
To effectively lift (0.25) (80kg) = 20 kg the mass of displaced air would be 20 kg. Density of air is about 1.2 kg/m3. From density = mass/volume, the volume of 20 kg of air, also the volume of the baloon (neglecting the mass of the helium) would be volume = mass/density (20kg/1.2 kg/m3) = 17 m3.
Estimate the buoyant force that air exerts on you. (To do this, you can estimate your volume by knowing your weight and by assuming that your weight density is a bit less than that of water).
To find the buoyant force that the air exerts on you, find your volume and multiply by the weight density of air. The mass of 1 m3 of air is about 1.25 kg. Multiple this by 10 N/kg and you get 12.5 N/m3. You can est. your volume by your weight and assuming your density is approx. equal to that of water. The weight density of water is 10^4 N/m3, which we'll assume is your density. By ratio and proportion (your weight in newtons)/(your volume in meters^3) If your weight is a heavy 1000 N for example (about 220 lbs), your volume is 0.1 m3, so buoyant force = 12.25 N/m3 x 0.1 m3 = about 1/2 N, roughly the weight of an apple.
We can understand how pressure in water depends on depth by considering a stack of bricks. The pressure below the bottom brick is determined by the weight of the entire stack. Halfway up the stack, the pressure is half because the weight of the bricks above is half. To explain atmospheric pressure we should consider compressible bricks, like those made of foam rubber. Why is this so?
Unlike water, air is easily compressed. In fact, its density is proportional to its pressure (at a given temperature). So, near the ground, where pressure is greater, the air's density is greater and corresponds to more squashed bricks; at high altitude, where the pressure is less, the air's density is less, corresponding to less squashed bricks.
Hold a spoon in a stream of water as shown and feel the effect of the differences in pressure.
Water pressure is lowered in the part flowing over the curved part of the spoon, resulting in that part moving toward the stream instead of away from it.
What happens to the internal pressure in a fluid flowing in a horizontal pipe when its speed decreases?
When speed decreases, internal pressure increases.
What happens to the internal pressure in a fluid flowing in a horizontal pipe when its speed increases?
When speed increases, internal pressure decreases.
The valve stem on a tire must exert a certain force on the air within to prevent any of that air from leaking out. If the diameter of the valve stem were doubled, by how much would the force exerted by the valve stem increase?
When the diameter is doubled, the area is four times as much. For the same pressure, this would mean four times as much force.
Lower a narrow glass tube or drinking straw into water and place your finger over the top of the tube. Lift the tube from the water and then lift your finger from the top of the tube. What happens?
When your finger closes the top of the water-filled straw, atmospheric pressure no longer acts on the top part of the water, which is easily lifted. When you raise your finger the water spills out the bottom. This is a nice procedure for transferring liquids from one test tube to another.
Is pressure greater or less in regions where streamlines are crowded?
Where streamlines are crowded, pressure is less.
Your friend says that the buoyant force of the atmosphere on an elephant is significantly greater than the buoyant force of the atmosphere on a small helium-filled balloon. Discuss your response.
You agree with your friend, the elephant displaces far more air than a small helium-filled ballon, or small anything. The effects of the buoyant forces, however, is a different story. The large buoyant force on the elephant is insignificant relative to its enormous weight. Not so for the tiny buoyant force acting on the balloon of tiny weight.
Raise a submerged upside-down glass that is full of water above the waterline, but with its mouth beneath the surface. Why doesn't the water run out? How tall would the glass have to be before water began to run out?
You have a barometer of sorts, but since the medium is water, it would have to reach a column 10.3 m tall to give you the same pressure as a column of mercury 76 cm tall.
On a perfect fall day, you are hovering at low altitude in a hot-air ballon, accelerating neither upward or downward. The total weight of the balloon, including its load and the hot air in it is 20,000 N. a. Show that the wright of the displaced air is 20,000 N. b. Show that the volume of the displaced air is 1700 m3.
a)The weight of the displaced air must be the same as the weight supported, since the total force (gravity plus buoyancy) is zero. The displaced air weighs 20,000 N. b) since weight = mg, the mass displaced air is m=W/g = 20,000 N/10 m/s2 = 2000 kg. Since density is mass/volume, the volume of the displaced air is volume= mass/density = 2000 kg/1.2 kg/m3 = 1700 m3 (g = 9.8 m/s2)
Comparing the spacing of streamlines around a tossed baseball that doesn't spin in flight with the spacing of streamlines around a ball that does. Why does the spinning baseball veer from the course of a nonspinning one?
Spacing of airstreams on opposite sides of a non-spinning ball are the same. For a spinning ball, airstream spacings are less on the side where airspeed is increased by spin action.
What are streamlines?
Streamlines are imaginary lines that show the path of a fluid.
What is the energy source for the motion of gas in the atmosphere? What prevents atmospheric gases from flying off into space ?
The Sun is the energy source for motion of air molecules. Earth's gravity pulls air molecules down, keeping most from escaping into space.
A little girl sits in a car at a traffic light holding a helium filled balloon. The windows are closed and the car is relatively airtight. When the light turns green and the car accelerates forward, her head pitches backward but the ballon pitches forward. Explain why.
The air tends to pitch toward the rear (law of inertia), becoming momentarily denser at the rear of the car, less dense in the front. Because the air is a gas obeying Boyle's law, its pressure is greater where its density is greater. Then the air has both a vertical and a horizontal "pressure gradient". The vertical gradient, arising from the weight of the atmosphere, buoys the balloon up. The horizontal gradient, arising from the acceleration, buoys the balloon forward. So the string of the balloon makes and angle. The pitch of the balloon will always be in the direction of acceleration. Step on the breaks and the balloon pitches backwards. Round a corner and the balloon noticeable leans radially toward the center of the curve.
Heat a small amount of water to boiling in an aluminum soda-pop can and invert it quickly into a dish of cooler water.
The aluminum can implodes dramatically. What occurs is rapid condensation of the steam, described later in Ch 18. This is a must-do activity!
Why won't a vacuum pump operate for a well that is deeper than 10.3 m?
The atmosphere can push water a maximum of 10.3 m via its pressure.
Why are high-altitude research balloons only partially inflated when launched?
The balloons expand and would likely rupture with increased altitude if fully inflated.
Push a pin through a small card and place it in the hole of a thread spool. Try to blow the card from the spool by blowing through the hole, as Evan Jones does in one of the chapter-opening photos. Try it in all directions.
The blown air that spreads between the spool and card is of low pressure, low enough that the greater atmospheric pressure on the outside part of the card presses the card to the spool.
When an air bubble rises is water, what happens to its mass, volume, and density?
The bubble's mass does not change. It's volume increases because the pressure decreases (Boyle's law), and its density decreases (same mass, more volume).
When you replace helium in a balloon with less-dense hydrogen, does the buoyant force on the balloon change if the balloon remains the same size? Explain.
The buoyant force does not change, because the volume of the balloon does not change. The buoyant force is the weight of air displaced, and doesn't depend on what is doing the displacing. The net lift, however, is greater because of a smaller weight of gas.
What is the cause of atmospheric pressure?
The cause of atmospheric pressure is the weight of air.
How does the density of air in a deep mine compare with the air density at Earth's surface?
The density of air in a deep mine is greater than at the surface. The air filling up the mine adds weight and pressure at the bottom of the mine, and according to Boyle's law, greater pressure in a gas means greater density.
Two identical balloons of the same volume are pumped up with air to more than atmospheric pressure and suspended on the ends of a stick that is horizontally balanced. One of the balloons is then punctured. Discuss whether or not the balance of the stick is upset. If so, which way does it tip?
The end supporting the punctured balloon tips upward as it is lightened by the amount of air that escapes. There is also a loss of buoyant force on the punctured balloon, but that loss of upward force is less than the loss of downward force, since the density of air in the balloon before puncturing was greater than the density of surrounding air.
Is the fluid that foes up the inside tube in a hand sprayer pushed up the tube or sucked up the tube? Explain.
The fluid is pushed up by the pressure of the atmosphere on its surface.
The force of the atmosphere at sea level against the outside of a 10-m2 store window is about a million N. Why doesn't this shatter the window? Why might the window shatter in a strong wind blowing past the window?
The force of the atmosphere is on both sides of the window; the net force is zero, so windows don't normally break under the weight of the atmosphere. In a strong wind, however, pressure will be reduced on the windward side (Bernoulli's principle) and the forces no longer cancel to zero. Many windows are blown outward in strong winds.
Invert a water-filled pop bottle or a small-necked jar. Notice that the water doesn't simply fall out but gurgles out of the container. Air pressure won't let it escape until some air has pushed its way up inside the bottle to occupy the space above the liquid. How would an inverted, water-filled bottle empty on the moon.
The gurgling is due to air entering the jar. No gurgling would occur if this were somehow tried on the moon where there is no atmosphere.
Why doesn't the size of the cross-sectional area of a mercury barometer affect the height of the enclosed mercury column?
The height of the column in a mercury barometer is determined by pressure, not force. Fluid pressures depend on density and depth - pressure at the bottom of a wide column of mercury is no different than at the bottom of a narrow column of mercury at the same depth. The weight of fluid per area of contact is the same for each. Also with the surrounding air, hence why wide and narrow-tube barometers show the same height.
If you could somehow replace the mercury in a mercury barometer with a denser liquid, would the height of the liquid column be greater than or less than the height of the mercury? Why?
The height would be less. The weight of the column balances the weight of an equal area column of air. The denser liquid would need less height to have the same weight as the mercury column.
How does the concept of buoyancy complicate the old question "Which weighs more: a pound of lead or a pound of feathers?"
The lead and feathers have the same mass. Weight is measured as the force with which something presses on a supporting surface. When the buoyancy of air plays a role, the net force against the supporting surface is less, indicating a smaller weight. Buoyancy force is more appreciable for larger volumes, like feathers. So with less buoyancy, the same mass of lead weighs more than the same mass of feathers.
What is the mass of a cubic meter of air at room temperature (20 C)?
The mass of one cubic meter of air is about 1.25 kg.
What, if anything, happens to the pressure of the gas in a rubber balloon when the balloon is squeezed smaller?
The pressure increases, in accord with Boyle's law.
Why is it that an aneroid barometer is able to measure altitude as well as atmospheric pressure?
The pressure sensed by an aneroid barometer is calibrated in altitude.
Compare the pressure exerted by the tires of your car on the road with the air pressure in the tires.
The pressures should be approximately the same. The rigid walls of the tire prevent the pressure calculations from being closer. The calculated value should therefore be somewhat greater.
When you drink liquid through a straw, is it more accurate to say the liquid is pushed up the straw rather than sucked up the straw? What exactly does the pushing? Defend your answer.
Correct to say pushed up. The pressure of the surrounding air does the pushing.
What is the purpose of the ridges that prevent the funnel from fitting tightly in the mouth of a bottle?
The ridges near the base of the funnel allow air to escape from a container it is inserted into. Without the ridges, air in the container would be compressed and would tend to prevent filling as the level of liquid rises.
You and your friendly car dealer float a long string of closely spaced helium-filled balloons over his used-car lot. You secure the two ends of the long string of balloons to different points on the ground so that the balloons float over the lot in an arc. What is the name of this arc?
The shape would be a catenary.
Are the ships in the preceding question sucked together or pushed together? Explain
The ships are pushed together by the greater water pressure on their opposite sides.
The gas pressure inside an inflated rubber balloon is always greater than the air pressure outside. Explain.
The stretched rubber of an inflated balloon provides an inward pressure. So the pressure inside is balanced by the sum of two pressures; the outside air pressure plus the pressure of the stretched ballon. The fact that air pressure is greater inside an inflated ballon than outside is evident when it is punctured - the air "explodes" outward.
Why are runways longer for takeoffs and landings at high-altitude airports, such as those in Denver and Mexico City?
The thinner air at high-altitude airports produces less lift for aircraft. This means aircraft need longer runways to achieve greater speed for takeoff.
Why is the pressure in an automobiles tires slightly greater after the car has been driven several kilometers?
The tires heat, giving additional motion to the gases molecules within.
What, if anything, happens to the volume of gas in an atmospheric research-type balloon when it is heated?
The volume of gas in the balloon increases.
If you count the tires on a large tractor-trailer that is unloading food at your local supermarket, you may be surprised to count 18 tires. Why so many tires?
The weight of a truck is distributed over the part of the tires that make contact with the road. Weight/surface area = pressure ,so the greater the surface area, or equivalently, the greater the number of tires, the greater the weight of the truck can be for a given pressure. What pressure? The pressure exerted by the tires on the road, which is determined by (but is somewhat greater than) the air pressure in its tires.
