Chapter 13

Front 1

Relationship between liquid pressure and depth of a liquid? Between pressure and density

Back 1

Liquid Pressure= Weight density X depth

Liquid pressure is directly proportional to the density and depth. As the density or
depth of the liquid increases, the liquid pressure will also increase by the same magnitude.

Front 2

If you swim beneath the surface in salt water, will the pressure be greater than in freshwater at the same depth? Why or why not?

Back 2

Salt water is denser than fresh water. Pressure will be greater beneath the salt water than the fresh water at the same depth.

Front 3

How does water pressure one meter below the surface of a small pond compare with water pressure one meter below the surface of a huge lake?

Back 3

The pressures will be equal. The pressure on an object submerged in a fluid does not depend on the surface area of the fluid or object.

Front 4

If you punch a hole in a container filled with water, in what direction does the water initially flow outward from the container?

Back 4

Initial flow is perpendicular to the surface of the container.

Front 5

Why does the buoyant force act upward on an object submerged in water?

Back 5

Buoyant force is a reaction force which acts opposite to the gravitational pull of Earth. As weight is always directed toward the center of Earth, the buoyancy force acts upward.

Greater pressure against bottom

Front 6

How does the volume of a completely submerged object compare with the volume of water displaced?

Back 6

The volume of the completely submerged object is equal to the volume of displaced water.

Front 7

How does the buoyant force on a submerged object compare with the weight of water displaced?

Back 7

Same

Front 8

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?

Back 8

Vdisplaced= 1/2 (volume)
1/2 (1 L) = .5 L

Buoyant force = 4.9 N

Front 9

Is the buoyant force on a submerged object equal to the weight of the object itself or equal to the weight of the fluid displaced by the object?

Back 9

Equals the weight of fluid displaced by the object.

Front 10

Does the buoyant force on a submerged object depend on the volume of the object or the weight of the object?

Back 10

Volume

Front 11

How is the density of a fish controlled? How is the density of a submarine controlled?

Back 11

A fish changes its volume via its air sac it can move upward by increasing its volume, downed by contracting its density; a submarine changes its weight by taking on or expelling water in its ballast tanks.

Front 12

What weight of water is displaced by a 100-ton ship? What is the buoyant force that acts on a floating 100-ton ship?

Back 12

100 tons; 100 tons; Principle of Flotation

Front 13

What happens to the pressure in all parts of a confined fluid if the pressure in one part in increased?

Back 13

According to Pascal’s law, the pressure will be equally increased in all parts of the confined fluid.

Front 14

If the pressure in a hydraulic press is increased by an additional 10 N/cm^2, how much extra load will the output piston support if its cross-sectional area is 50 cm^2?

Back 14

- An additional 10 N/cm2 means an additional 10 N on each square cm, which means the piston will support an extra load of 50 x 10 N
= 500 N.

Front 15

The sketch shows a reservoir that supplies water to a farm. It is made of wood and is reinforced with metal hoops. A) Why is it elevated? B) Why are the hoops closer together near the bottom part of a tank?

Back 15

A) It is elevated, to increase the pressure below
B) Because at the bottom of the hoop, the pressure is greater (more depth)

Front 16

When you are bathing on a stony beach, why do the stones hurt your feet less when you’re standing in deep water?

Back 16

Deeper water, more buoyancy, resulting in less pressure between you and the stones.
- less pressure between you and the rocks

Front 17

If liquid pressure were the same at all depths, would there be a buoyant force on an object submerged in the liquid? Explain.

Back 17

No; buoyant force is a result of a difference in pressure

Front 18

How much force is needed to push a nearly weightless but rigid 1-L carton beneath a surface of water?

Back 18

Force needs is weight of 1 L of water, 10 N

Front 19

A piece of iron placed on a block of wood makes it float lower in the water. If the iron were instead suspended beneath the wood, would it float as low, lower, or higher? Defend your answer.

Back 19

The wood would float higher because when the iron is placed in the water, there is a force of bouyancy acting on it in the upward direction, thus there is less force pressing the wood into the water than before when the iron was totally on top of the wood.

Front 20

A ship sailing from the ocean into a freshwater harbor sinks slightly deeper into the water. Does the buoyant force on the ship change? If so, does it increase or decrease?

Back 20

No change in buoyant force; when floating the buoyant force is equal to weight of the floating object

Front 21

The relative densities of water, ice, and alcohol are 1.0, 0.9, and 0.8 respectively. Do ice cubes float higher or lower in a mixed alcoholic drink? What comment can you make about a cocktail in which the ice cubes lie submerged at the bottom of the glass?

Back 21

Whether an ice cube will float or sink in a mixed alcohol drink depends on the average density of the alcohol and water in a mixed drink. If the ice cubes lie submerged in a cocktail, there must be more alcohol than water in the drink, since the average density of the mixture must be less than that of ice.

Front 22

Calculate the water pressure at the bottom of the 100 m high water tower shown in figure 13.2.

Back 22

- p= hdg
- p = 100 X 1,000 X 10
- = 10^6 pascal

Front 23

An ice cube measures 10 cm on a side and floats in water. One cm extends above water level. If you shaved off the 1 cm part, how many cm of the reaming ice would extend above water level?

Back 23

The same length of the remaining ice would extend over the water level

Front 24

In the hydraulic pistons shown in the sketch, the small piston has a diameter of 2 cm. The larger piston has a diameter of 6 cm. How much more force can the larger piston exert compared with the force applied to the smaller piston?

Back 24

The relative area squares of diameters; 6^2/2^2 36/4 9. Large piston output force is 9 times as great as the input force to smaller piston.