Chapter 13 Physics- Liquids
If a 1-L container is immersed halfway into water, what is the volume of water displaced? What is the buoyant force on the container?
0.5 L displaced, 5 N buoyant force
Buoyant force is greatest on a submerged
1-cubic centimeter block of aluminum and 1-cubic centimeter block of lead. same for each
What is the buoyant force acting on a 10-ton ship floating in the ocean? A. less than 10 tons B. 10 tons C. more than 10 tons D. depends on density of sea water
10 tons
The buoyant force acting on a 10-ton ship floating in the ocean is
10 tons. For any ship floating at rest, the net force acting on it is zero - that's 10 tons downward, 10 tons, upward. The 10-ton ship is in equilibrium, no matter the density of the water.
If an object submerged in water displaces 10 kg of water, the buoyant force on the submerged object is 100 N 10 kg 10 N more than 100 N
100 N
density of freshwater
1000 kg/m^3
Rank, from smallest to largest, the pressures in the tank of motionless fluid shown in the figure.
A BCD E F
archimedes principles
A body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid.
How is the density of a fish controlled? How is the density of a submarine controlled?
A fish changes its volume, whereas a submarine changes its weight.
Consider the set of tubes shown in the figure. Each tube contains an unknown fluid that is less dense than the water it floats on top of. Rank the four unknown fluids from least dense to most dense.
AC B D
What is the difference between adhesion and cohesion?
Adhesion is the force between a liquid and the inner surface of its tube. Cohesion is the binding force between molecules in a liquid.
Distinguish between adhesive and cohesive forces.
Adhesive forces are between unlike substances, whereas cohesive forces are between like substances.
Archimedes' Principle
An immersed object is buoyed up by a force equal to the weight of the fluid it displaces.
On a boat ride, the skipper gives you a life preserver filled with lead pellets. When he sees the skeptical look on your face, he says that you'll experience a greater buoyant force if you fall overboard than your friends who wear Styrofoam-filled preservers. A. He is correct about the buoyancy and you have nothing to fear. B. He is correct about the buoyancy, but you will nevertheless sink. C. He is incorrect about the buoyancy, but you will float anyway. D. He is completely incorrect.
B. He is correct about the buoyancy, but you will nevertheless sink
How does the water pressure 1 m below the surface of a small pond compare with the water pressure 1 m below the surface of a huge lake?
Because both densities and depths are the same, the two pressures are the same.
How does the water pressure 1 m below the surface of ocean water compare with the water pressure 1 m below the surface of a huge lake?
Because ocean water is saltwater, its density is greater than the density of lake fresh water, pressure at equal depths is greater in saltwater.
Which favors water-striding insects that skip across a water surface—warm water or cool water?
Cooler water with its somewhat greater surface tension is more favorable to water striders than warmer water. Interestingly, they are proficient in both warm and cool water.
The reason that buoyant force acts upward on a submerged object is that A. it acts in a direction to oppose gravity. B. if it acted downward, nothing would float. C. the weight of fluid displaced reacts with an upward force. D. upward pressure against the bottom is greater than downward pressure against the top of the submerged object.
D. upward pressure against the bottom is greater than downward pressure against the top of the submerged object.
Why is there no horizontal buoyant force on a submerged object?
Force vectors on the sides cancel one another.
If you punch holes in the side of a container filled with water, in what direction does the water initially flow outward from the container?
It flows straight out, perpendicular to the wall.
When Dr. Hewitt immerses the object in water, how does the loss of weight of the object compare with the buoyant force of the water?
Loss of weight is equal to the buoyant force.
Fill in the blanks: An object denser than water will _______ in water. An object less dense than water will _______ in water. An object with the same density as water will _______ in water. Float, sink, float Sink, float, sink Sink, float, neither sink nor float Float, sink, neither sink nor float
Sink, float, neither sink nor float
Why do the gondolas of the Falkirk Wheel (see Figure 13.19 in the textbook) have the same weight whether or not they carry boats?
The boats displace water out of the gondolas equal to their weights.
A 1-L container completely filled with lead has a mass of 11.3 kg and is submerged in water. What is the buoyant force acting on it?
The buoyant force equals the weight of the liter of water displaced—not the weight of the lead! One L of water has a mass of 1 kg and weighs 10 N. So the buoyant force on it is 10 N.
What is the buoyant force that acts on a submerged object equal to?
The buoyant force is equal to the weight of the fluid displaced by the submerged object.
As a boulder thrown into a deep lake sinks deeper and deeper into the water, does the buoyant force on it increase or decrease?
The buoyant force remains unchanged as the boulder sinks because the boulder displaces the same volume and the same weight of water at any depth.
The large piston of a hydraulic lift has an area twice the area of the small piston. In comparison to a force applied on the small piston, what would the force exerted by the large piston be? The large piston would have half the force. The large piston would have double the force. The large piston would have a larger force. The large piston would have the same force.
The large piston would have double the force.
There is a condition in which the buoyant force on an object does equal the weight of the object. What is this condition? The object is neutrally buoyant, so it will neither sink nor float. It will float It will float almost completely out of the water. It will sink.
The object is neutrally buoyant, so it will neither sink nor float.
What happens to the pressure in all parts of a confined fluid if the pressure in one part is increased?
The pressure everywhere increases by the same amount.
Why does the buoyant force act upward on an object submerged in water?
The pressure upward on the deeper bottom is greater than the downward pressure on the top.
If you swim beneath the surface in saltwater, will the pressure be greater than in freshwater at the same depth? Why or why not?
The pressure will be greater because saltwater is more dense.
When Dr. Hewitt immerses an object in water the second time and catches the water that is displaced by the object, how does the weight lost by the object compare to the weight of the water displaced?
The weight loss of the object is equal to the weight of the water displaced.
True or false: Archimedes' principle tells us that any object that displaces 10 N of liquid will be buoyed up with 10 N.
True. It's only the weight of the displaced liquid that counts. (Also look at it in a Newton's third law way: If the immersed object pushes 10 N of fluid aside, the displaced fluid reacts by pushing back on the immersed object with 10 N.)
What is the pressure of water against the bottom of a 20-cm tall 10-kg beaker of water resting on a supporting surface?
Water pressure is weight density of water in meters (10,000N/M3), which is 10,000 N/M3 x 0.20m=2000n/m2 . Notice that the weight of water in the beaker is not a factor. Density and depth are all you need to know for pressure in still water
How much average force does each of the 600 nails exert on 60-kg Sara in Figure 13.2? What is the average force per nail for 300 nails of support? For one nail?
We convert mass 60 kg to the force of gravity that Sara exerts on the nails. 60kg x 10N/1kg=600N . The force per nail is then 600 N/ 600 nails= 1Nper nail, which is quite tolerable, like the weight of an apple on each nail. For half as many nails the pressure is 600N/300 nails=2N per nail, a bit uncomfortable. For one nail, pressure is 600N/ 1nail= 600N per nail (a giant no no!).
How does weakening of bonding between molecules in a liquid affect surface tension?
Weaker bonding results in a lowering of surface tension.
liquid pressure is exerted equally in
all directions
Buoyant force is greater on a submerged 10-newton block of
aluminum. A 10-ton block of aluminum has more volume than a 10-ton block of lead. So when submerged, the aluminum block with its greater volume displaces more fluid than the more compact block of lead, meaning more BF on the block of aluminum
Consider Two Tubes Filled With Water at the Same Height, One With Freshwater and the Other With Saltwater. The Pressure Is Greater at the Bottom of the Tube With a) freshwater. b) saltwater. c) Both the same. d) Depends on whether the tubes have the same cross-sectional area.
b. saltwater
If a weighted air-filled balloon sinks in deep water, it will
be acted on by a continuously decreasing buoyant force.
Water pressure is greatest against the
bottom of a submerged object
Water pressure is greatest against the A. top of a submerged object. B. bottom of a submerged object. C. sides of a submerged object. D. is the same against all surfaces. E. none of these.
bottom of a submerged object
Water pressure on a submerged object is greatest against its
bottom. Pressure depends on depth and fluid density. Since the bottom of an object is always deeper than the top, the bottom receives more pressure for the same density of fluid.
The operation of a hydraulic press best illustrates Archimedes' principle differences in pressure conservation of energy streamline flow of fluids
conservation of energy
The pressure increases on a block resting on a table when you increase the surface area downward force on the block density of the block downward force and surface area
downward force on the block
in a hydraulic-press operation, it is impossible for the
energy output to exceed the energy input
An object that has a density ___ to the density of the fluid in which it is immersed will neither sink nor float.
equal
Water pressure in a lake is greater midway to the bottom the same at any point greater at the bottom greater at the surface
greater at the bottom
A scuba diver is planning to dive to the same depth in the open ocean and in a deep lake. Considering that salt water is denser that fresh water, where would the diver feel more pressure? Same in both In the lake We need to know the depth of the diver to answer this question. In the ocean
in the ocean
Water pressure provided by a water tower is greater if the tower A. is taller. B. holds more water. C. Both A and B. D. None of the above.
is taller
water pressure provided by a water tower is greater if the tower
is taller
A loaded ship arrives at the first freshwater lock of the Panama Canal, will it float higher or lower than in the open ocean? I need to know the weight of the ship to answer. It will float higher. It will float at the same level. It will float lower.
it will float lower
An object ____ dense than the fluid in which it is immersed will float.
less
A lobster crawls onto a bathroom scale on the ocean floor. Its weight compared to its weight above the surface is
less. The reading on a weighing scale is mg downward minus BF upward. In air, the BF of displaced air is negligible. But not negligible for a weighing scale submerged in ocean water. In effect, the BF "lifts" one off the scale, lowering the scale reading, whether for a lobster or a scuba diver.
A basketball floats in various liquids. Rank the percentage of its volume above the water line, from most to least for the following: Floating in freshwater saltwater mercury
mercury saltwater freshwater
An object ____ dense than the fluid in which it is immersed will sink.
more
Buoyant force acts upward on a submerged object because
pressure against its bottom is greater than pressure against its top.
Pascal's Principle
pressure applied to a fluid is transmitted throughout the fluid
When You Stand on Tiptoes on a Bathroom Scale, There Is an Increase In a) weight reading. b) pressure on the scale. c) both weight and pressure on the scale. d) None of these
pressure on the scale
A key feature of the Falkirk Wheel in Scotland is that opposite gondolas have the same weight when both are brim-full of water
regardless of the weights of boats or no boats in each.
Two life preservers have identical volumes, but one is filled with styrofoam while the other is filled with sand. When the two life preservers are fully submerged, the buoyant force is greater on the one filled with a. styrofoam. b. sand. c. same on each as long as their volumes are the same
same on each as long as their volumes are the same
A stone of volume V submerged in water displaces the same volume and weight of water same weight of water same density times volume same volume of water
same volume of water
To multiply the input force of a hydraulic lift , the input end should be the one having the
smaller diameter piston
What geometrical shape has the least surface area for a given volume? Cube Cylinder Sphere Disk
sphere
The pressure at the bottom of a jug filled with water does NOT depend on
surface area of the water
The pressure at the bottom of a jug filled with water does NOT depend on a. water density. b. the height of the liquid. c. none of the given variants d. the acceleration due to gravity. e. surface area of the water
surface area of the water
capillarity
the attraction between molecules that results in the rise of a liquid in small tubes
surface tension
the force that acts on the surface of a liquid and that tends to minimize the area of the surface
How does water pressure 2 m below the surface of a small pond compare with water pressure 2 m below the surface of a huge lake? The pressure will be greater. The pressure will be the same. The pressure will be zero in both cases. The pressure will be less.
the pressure will be the same
The caissons of the Falkirk Wheel are balanced only when their water levels are the same the same number of boats are in each boats are not heavily loaded they carry boats of equal weights
their water levels are the same
A large ice cube containing an iron railroad spike floats in a brim-full container of water. When the ice cube melts,
water level drops. Just as water level drops when a heavy boulder is tossed overboard from a boat, the water level drops when the floating ice cube releases its iron cargo. When iron is floating in a boat or in frozen ice, it displaces its weight of water. When submerged it displaces its volume of water, significantly less. Water level drops.
A dam is thicker at the bottom than at the top partly because
water pressure is greater with increasing depth
A dam is thicker at the bottom than at the top partly because A. water is denser at deeper levels. B. water pressure is greater with increasing depth. C. surface tension exists only on the surface of liquids. D. it looks better. E. none of these
water pressure is greater with increasing depth
liquid pressure is
weight density x depth
Which will remain the same for two identical books, one lying flat and the other standing on its end?
weight will remain the same
A consequence of surface tension for water is
wet sand being firmer than dry sand.
