Physics Chapter 13
The pressure in a liquid depends on liquid
-depth -density
An egg rests at the bottom of a bowl filled with water. When salt is slowly added to the water the egg rises and floats, from which we conclude
-salt water is denser than an egg -salt water is denser than fresh water
A fish normally displaces its own
-weight of water -volume of water
If a 1-L container is immersed halfway into water, what is the volume of the water displaced? What is the buoyant force on the container?
0.5 L displaced, 5 N buoyant force
If an object suspended by a scale shows a weight of 3 N in air, and 2 N when submerged in water, the buoyant force on the submerged object is __________.
1 N
What is the mass of 1 L of water? What is its weight in newtons?
1 kg; 10 N
One liter of water has a mass of
1 kilogram
Buoyant force is greater on a submerged
1-kg block of aluminum
The buoyant force acting on a 10-ton ship floating in the ocean is
10 tons
How much air must a 100-ton blimp displace to float and neither rise nor sink?
100 tons
What is the weight of water displaced by a 100-ton floating ship?
100 tons
The mass of a cubic meter of water is
1000 kg
In lab you find that a 1-kg rock suspended above water weighs 10 N . When the rock is suspended beneath the surface of the water, the scale reads 8.0 N. If the container of water weighs 10 N on the weighing scale, what is the scale reading when the rock is suspended beneath the surface of the water?
12 N -If the container of water on a bathroom-type scale weighs 9.8 N, what is the scale reading when the rock is suspended beneath the surface of the water? Newton's third law says that if the water pushes the rock up then the rock pushes down on the water with an equal and opposite force. Therefore the rock pushes down on the water with a force of 2N. When this is added to the initial scale reading we get 11.8 N
A scale from which a rock is suspended reads 5 N when the rock is out of water and 3 N when the rock is submerged. Buoyant force on the rock is
2 N
In lab you find that a 1-kg rock suspended above water weighs 10 N . When the rock is suspended beneath the surface of the water, the scale reads 8.0 N. What is the buoyant force on the rock?
2 N -Two forces are acting upwards on the rock, the hook scale and the upthrust. The sum of these two forces must balance the weight of the rock, 9.8 N. Therefore the upthrust = 9.8N - 7.8N = 2N
In lab you find that a 1-kg rock suspended above water weighs 10 N . When the rock is suspended beneath the surface of the water, the scale reads 8.0 N. What is the scale reading when the rock is released and rests at the bottom of the container?
20 N -What is the scale reading when the rock is released and rests at the bottom of the container? When the rock is released the spring balance will have to support the weight of the rock as well as the weight of the water and container, bringing the reading to 9.8N + 9.8N = 19.6N
How much force is needed to hold a nearly weightless but rigid 1-L carton beneath the surface of water?
9.8N
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
Why isn't there a horizontal buoyant force on a submerged object?
Force vectors on the sides cancel one another
Is the buoyant force on a submerged object equal to the weight of the object itself or is it equal to the weight of the fluid displaced by the object?
It is equal to the weight of the fluid displaced
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
What is the cause of surface tension?
Molecular attraction
How does pressure relate to force?
Pressure is force per unit area
What is the relationship between liquid pressure and the depth of a liquid? Between liquid pressure and weight density?
Pressure is proportional to both depth and weight density
What will these objects do in water: an object denser than water, an object less dense than water, an object that has the same density as water.
Sink, float, neither float nor sink
What geometrical shape has the smallest surface area for a given volume?
Sphere
The attraction between unlike substances is called
adhesion
Water pressure in a lake is greater __________.
at the bottom
Water pressure on a submerged object is greatest against its
bottom
On what factors does the buoyant force acting on an object depend?
height of the object
When a boat sails from fresh water to salt water, the boat will float
higher in the water
If you float a piece of wood in a container half-full of water that rests on a weighing scale, the weight reading on the scale will
increase
The volume of water displaced by a floating 20-ton boat
is the volume of 20 tons of water
Buoyant force is greater on a submerged 1-cubic centimeter block of
lead and aluminum - same on each
A block of aluminum with a mass of 1 kg is placed in a beaker of water filled to the brim. Water overflows. The same is done in another beaker with a 1-kg block of lead. Does the lead displace more, less, or the same amount of water?
less
A lobster crawls onto a bathroom scale on the ocean floor. Its weight compared to its weight above the surface is
less
The amount of water displaced by a liter-sized block of ordinary wood floating in water is
less than 1 liter
Pumice is a volcanic rock that floats, which means its density is
less than the density of water
A person floats higher in the dense water of the Dead Sea because
less volume of water is displaced
Compared to an empty ship, the same ship loaded with Styrofoam will float
lower in the water
Surface tension is caused by __________.
molecular attractions
Buoyant force acts upward on a submerged object because
pressure against its bottom is greater than pressure against its top
An ice cube floating in a glass of water contains many air bubbles. When the ice melts, the water level will
remain unchanged
If you float a piece of wood in a container brim-full of water that rests on a weighing scale, some water will spill. Then the weight reading on the scale will
remain unchanged
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
same on each as long as their volumes are the same
The pressure at the bottom of a jug filled with water does NOT depend on
surface area of the water
When holes are drilled through the wall of a water tower, water will spurt out with the greatest speed from the hole closest to
the bottom of the tower
The reason a life jacket helps keep you afloat is
the density of both you and the jacket together is less than your density alone
Compared to the density of water, the density of a fish is
the same
A block of aluminum with a volume of 10 cm3 is placed in a beaker of water filled to the brim. Water overflows. The same is done in another beaker with a 10-cm3 block of lead. Does the lead displace more, less, or the same amount of water?
the same amount
When you stand with only one of your feet on a weighing scale, the scale reading is
the same as with both feet
A completely submerged object always displaces its own
volume of fluid
A hospital patient confined to bed will be less likely to develop bed sores with a
water bed
A dam is thicker at the bottom than at the top mainly because
water pressure increases with depth
Which will remain the same for two identical books, one lying flat and the other standing on an end?
weight
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
How does the buoyant force on a submerged object compare with the weight of the water displaced?
The buoyant force is equal to the weight of the water displaced
Suppose you increase the depth of the object WITHOUT changing its height. What will happen to the force due to pressure on the bottom of the object?
The force due to pressure on the bottom of the object will increase
Suppose you increase the height of the object WITHOUT changing its depth under water. What will happen to the force due to pressure on the bottom of the object?
The force due to pressure on the bottom of the object will increase
Suppose you increase the height of the object WITHOUT changing its depth under water. What will happen to the net buoyant force?
The net buoyant force will increase
Suppose you increase the depth of the object WITHOUT changing its height. What will happen to the net buoyant force?
The net buoyant force will stay the same
What is the condition in which the buoyant force on an object does equal the weight of the object?
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
How does pressure at the bottom of a body of water relate to the weight of water above each square meter of the bottom surface?
The pressure is the weight of the water divided by 1 m^2
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 fresh water at the same depth?
The pressure will be greater
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?
The pressure will be the same
How does the volume of a completely submerged object compare with the volume of water displaced?
The volumes are equal
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
A mountain that floats on the mantle indicates that the density of the mantle is
greater than that of the mountain
Does the buoyant force on a submerged object depend on the volume of the object or on the weight of the object?
Volume
The attraction between like substances, stickiness, is called
cohesion
Surface tension is a direct result of
cohesive forces between molecules in a liquid
Surface tension of liquids
decreases as the liquid temperature increases
When you float in fresh water, the buoyant force that acts on you is equal to your weight. When you float higher in the denser water of the Dead Sea, the buoyant force that acts on you is
equal to your weight
While standing, your blood pressure is normally greatest in your
feet
The concept of pressure involves both
force and area
