Chapter 13 Liquids

Question 1

Definition, Formula and Unit for Pressure

Answer 1

The ration of force to the area over which that force is distributed:

Pressure=force/area

1 kg/(m·s²) = Pascal

Question 2

Definition, Formula & Units for Liquid Pressure

Answer 2

Liquid pressure depends on depth and the density of the liquid.

Liquid pressure= weight density X depth

Pascal (Pa)

Question 3

Where is Liquid Pressure greater on an object? Why?

Answer 3

Liquid Pressure acts perpendicular to the object and is dependent on depth. The depth at the bottom of the object is greater than at the top.

Question 4

Total Pressure Equal?

Answer 4

Liquid pressure (weight densityX depth) + atmospheric pressure

Question 5

What experience more pressure an object submerged 3m in a large but shallow lake, or the same object submerged 3m in a small but deep pond?

Answer 5

The pressure is the same for both circumstances since liquid pressure is dependent on depth not the amount of liquid present.

Question 6

How is liquid pressure different for any given depth below a surface? Does the shape of the container matter?

Answer 6

Liquid pressure is the same for any given depth below the surface, regardless of the shape of the containing vessel. Liquid pressure= weight density X depth (for total pressure add the air pressure at the top).

Question 7

How does liquid act on an object?

Answer 7

Liquid presses against a surface, there is a net force that is perpendicular to the surface. Although pressure doesn’t have a specific direction, force does. Although water is forced against each point from many directions the componenets of the forces that are not perpendicular to the surface cancel each other out.

Question 8

Suppose that when standing on a bathroom scale you raise one foot. Does the pressure you exert on the scale change? Is there a difference in the scale reading?

Question 9

Pressure=force/area

Standing on one foot reduced area therefore increasing the pressure. However the reading on the scale does not change since the scale measure weight (force).

Question 10

What is buoyancy?

Answer 10

Buoyancy is the apparent loss of weight of an object immersed or submerged in a fluid.

Question 11

What is the Buoyant Force?

Question 12

The buoyant force is the net upward force exerted by a fluid on a submerged or immersed object. It is a consequence of pressure increasing with depth. Forces due to water pressure are extered in every direction against the boulder. Vectors against the sides cancel out, so there is no horizontal buoyant force. Vertical forces due not cancel, and since the depth is greater at the bottom, the pressure is greater against the bottom. Since the upward forces against the bottom are greater than downward forces against the top, there is a net upward force=buoyant force.

Question 13

How much water is displaced when a stone is submerged in it?

Answer 13

Water is displaced by the stone. The volume of the stone (the amount of space it taes up) is equal to the volume of the water displaced. A completely submerged object always displaces a volume of liquid equal to its own volume.

Question 14

What is Archimedes’ Principle? What is the buoyant force if an immersed object displace 1kg of fluid?

Answer 14

**Archimedes’ Principle- An immersed object is buoyed up by a force equal to the weight of the fluid it displaces. ****If an immersed object displaces 1kg of fluid, the buoyant force acting on it equals to the weight of 1kg.

Buoyant Force= weight of fluid displaced

Question 15

What is the difference between immersed and submerged?

Answer 15

Immersion is just simply putting something inside the water, submersion means total immersion.

I.E. Your foot in water=immersion, your whole body immersed=submerged.

Question 16

If a 1L container is immersed halfway into the water, what is the buoyant force equal to? What if we submerged it?

Answer 16

If the 1L container is only immersed halfway, then the buoyant force **equals **the weight of 1/2L of water (no matter what is in the container). If the 1L container is submerd then the buoyant force **equals **the weight of 1L of water.

Question 17

How much is a liter of water in cm³? What is the mass of 1L of water? How much does it weigh?

Answer 17

1L=1000cm³

1L=1kg of water

1L=9.8N of water

Question 18

What is the density of water? What is it’s weight density?

Answer 18

Density of Water= 1 kg/L=1,000.00 kg/m³

Weight Density of Water= 9.8N/L

Question 19

What is the apparent weight of a 30kg object that displaces 20kg of fluid upon immersion?

Answer 19

10kg or 100N

Question 20

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?

Answer 20

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 1kg and weighs 10N. So the buoyant force on it is 10N.

Question 21

As a boulder thrown into a deep lake sinks deeper and deeper into the water, does the buoyant force upon it increase or decrease?

Answer 21

Buoyant force remains unchanged as the boulder sins, because the boulder displaces the same volume and same weight of water at any depth.

Question 22

Does Buoyant Force increase with depth? Why or why not?

Answer 22

Buoyant force DOES NOT increase with depth, because :

1. The amount of liquid displaced (weight of fluid displaced) does not change.
2. The difference between downward pressure acting on the top of the object, and the upward pressure acting against the bottom of the object, DOES NOT CHANGE. The pressures are different but the different is not.

Question 23

What Makes An Object Sink or Float?

Answer 23

Whether an object will sink or float in a liquid **DEPENDS **on how the buoyant force *compares with the object’s weight. *The object’s weight depends on the object’s density.

Question 24

What are the three simpel rules that determine whether an object will sink or float?

Answer 24

1. An object more dense than the fluid in which it is immersed will sink.
2. An object less dense than the fluid in which it is immersed will float.
3. An object having a density equal to the density of the fluid in which it is immersed will neither sink nor float.

Question 25

What should a person or object do to float?

Answer 25

To float you must reduce your density.

Weight density=weight/volume

This means that to reduce density you should either reduce the weight or increase the volume. For example wearing a life jacket increases volume and adds very little weight, resulting in a lesser density.

Question 26

Rule 3 of Sinking or floating: Fish

Answer 26

Fish neither sink nor float. A fish normally has the same density as water. Fish regulate their density by expanding and contracting an air sac in its body, changing volume and density.

Question 27

How does a submarine work?

Question 28

In a submarine weight (NOT VOLUME) is changed to achieve the desired density. Water is taken into or blown out of its ballast tanks.

Question 29

Two solid block of identical size are submerged in water. One block is lead and the other is aluminum. Upon which is the buoyant force greater?

Answer 29

The buoyant force is the same on each block because they displace the same volume of water. For submerged object, buoyant force is determined only by the volume of water displace, not the object’s weight.

Question 30

What is the Principle of Flotation?

Answer 30

The Principle of Flotation **states that **A floating object displaces a weight of fluid equal to its own weight. **When the buoyant force equals the weight of the object, the object will not sink farther.

Question 31

How does the density of the liquid affect Buoyant Force?

Answer 31

For a given volume of displaced fluid, a denser fluid exerts a greater buoyant force than a less dense fluid. A ship, therefore, floats higher in saltwater than in fresh water because saltwater is denser. Similarly a solid block of iron will float in mercury but not water (mercury is denser than water).

Question 32

Why is it easier for you to float in saltwater than in freshwater?

Answer 32

Saltwater is denser than freshwater, which means you don’t “sink” as far when displacing your weight.

Question 33

Does a life preserver filled with lead pellets experience a greater buoyant force than a styrofoam-filled life preserver? Which is more helpful to survival.

Answer 33

A life preserver filled with lead pellets does experience a greater buoyant force than a styrofoam-filled life preserver since it is denser and will be submerged displacing more water ( which means the weight of water displaced and threfore the buoyant force will increase). Whether you float or sink depends on whether or not the buoyant force equals your weight, a lead preserver will increase the buoyant force, but your weight would be increased by a much larger factor and you would drown.

Question 34

What is Pascal’s Principle?

Answer 34

Pascal’s Principle states that A change in pressure at any point in an enclosed fluid at rest is transmitted undiminished to all points in the fluid. REMEMBER THAT WHEN TALKING ABOUT PISTON’S THE AREA YOU SHOULD USE SHOULD BE A CIRCLE’S

2πr²

A 10kg load on a piston with an area of A, will support a 500g load on a piston with 50A area. (10kg*50=500kg)

Question 35

As the automobile in the figure is being lifter, how does the change in oil level in the reservoir compare with the distance the automobile moves?

Answer 35

The car moves up a greater distance that the oil level drops, since the area of the piston is smaller than the surface area of the oil in the reservoir.

Question 36

Define Surface Tension

Answer 36

**Surface Tension **is the tendency of the surface of a liquid to contract in area and thus behave like a stretched elastic membrane. Example, Rain Drops

Question 37

Define Capillarity

Answer 37

Capillarity is the rise of a liquid in a fine, hollow tuve or in a narrow space. Water molecules stick to the galss more than each other (adhesion) (opposite of cohesion). The films on the inner surface contracts more and raises water with it until the adhesive force is balanced by the weight of the water lifted. The narrower the tube the higher the water will be lifted.