Density and Pressure

Question 1

What is the formula for

density?

Answer 1

density = mass / volume

p = m / v

Question 2

What is density measured in?

Answer 2

grams per centimetre cubed (g/cm^3) or kilograms per metre cubed (kg/m^3)

Question 3

How can you measure an object’s

mass?

Answer 3

using a mass balance

Question 4

What is mass measured in?

Answer 4

kilograms (kg) or grams (g)

Question 5

How can you measure the volume of a regularly shaped object?

Answer 5

volume = width x height x length

v = a x b x c

Question 6

How can you measure the volume of an irregularly shaped object?

Answer 6

by submerging the object in water and finding how much water it displaces

(volume of object = volume 2 - volume 1)

(aka the displacement method)

Question 7

What is volume measured in?

Answer 7

m^3

Question 8

How woul you carry out the

displacement method?

Answer 8

Take a known volume of water in a measuring cylinder and fully submerge the object. The change in volume is your object’s volume.

Question 9

What is the formula for

pressure?

Answer 9

pressure = force / area

P = F / A

Question 10

What is area measured in?

Answer 10

m^2

Question 11

What is a

fluid?

Answer 11

a solid or a gas

Question 12

What is the formula for

pressure due to a liquid?

Answer 12

pressure = density x gravitational field strength x height

P = Pgh

to find the total pressure exerted by a fluid you need to add on atmospheric pressure

Question 13

What is pressure measured in?

Answer 13

Pascals (Pa) or Newtons per meter squared (N/m^2)

Question 14

What is height measured in?

Answer 14

metres (m)

Question 15

What is

Archimedes principle?

Answer 15

An object in a fluid is subject to an upward force that is equal to the weight of the fluid it displaces. This force is called upthrust. This force reduces the apparent weight of the object because the resultant force acting on it is lower.

Question 16

What is the formula for

weight?

(Archimedes principle)

Answer 16

weight = volume x density x gravity

W = vpg

(vogue)

Question 17

How do you calculate

apparent weight?

(Archimedes principle)

Answer 17

apparent weight = object weight - upthrust

Question 18

What is the formula for

the volume of a sphere?

Answer 18

v = 4πr^3 / 3

Question 19

What is the formula for

pressure due to gas?

(U-tube manometer)

Answer 19

pressure due to gas = pressure due to column of liquid + atmospheric pressure

Question 20

What is the formula for

pressure due to a column of liquid?

Answer 20

pressure = density x gravitational field strength x height

P = pgh

Question 21

(more to read and understand rather than anything else)

Explain how pumping water into and out of the buoyancy tank of a submarine affects the depth of the submarine below the surface.

[6]

Answer 21

Due to Archimedes principle, the amount of upthrust on the submarine will not change when water is added/removed from the tank because the amount of liquid displaced by the submarine stays the same because the submarine’s volume stays the same. So, as more water is added to the tank, the submarine’s weight will increase and may overcome the force of upthrust. This would lead the submarine to sink (and vice versa). If the water is pumped out of the tank, the amount of upthrust will overcome the submarine’s weight and the submarine will rise to the surface of the water. This concept applies across varying degrees.

[6]

all written by me I’d like to mention

Question 22

What is the general shape of a

solid?

Answer 22

regular, fixed, holds shape

Question 23

What is the general shape of a

liquid?

Answer 23

fluid, can change, fills bottom of container

Question 24

What is the general shape of a

gas?

Answer 24

fills container

Question 25

Can a solid be compressed?

Answer 25

no | (volume stays the same)

Question 26

Can a liquid be compressed?

Answer 26

no | (volume stays the same)

Question 27

Can a gas be compressed?

Answer 27

yes | (volume can change)

Question 28

# What is the general packing of atoms or molecules in a solid?

Answer 28

densely packed, arranged, vibrating

Question 29

# What is the general packing of atoms or molecules in a liquid?

Answer 29

relatively dense, molecules slide over each other

Question 30

# What is the general packing of atoms or molecules in a gas?

Answer 30

not very dense, molecules move freely

Question 31

# What are the general strength of forces in a solid?

Answer 31

strong forces of attraction

Question 32

# What are the general strength of forces in a liquid?

Answer 32

relatively strong forces of attraction

Question 33

# What are the general strength of forces in a gas?

Answer 33

weak forces of attraction

Question 34

# What is some evidence supporting kinetic theory?

Answer 34

- **crystals** and crystal structure - images from microscopes - **diffusion** of gases - brownian motion

Question 35

# Define brownian motion.

Answer 35

the **random** motion of particles in **suspension**

Question 36

# Why do air molecules move rapidly and randomly in all directions?

Answer 36

because they are being **bombarded** by other **air molecules** from **all sides**

Question 37

# Using the continuous movement of particles in a gas, explain why gases exert a pressure?

Answer 37

1. Gas particles are in **constant random motion**. 2. The particles **collide** with the walls of their container, which **changes** their **dircetion**. 3. A **change in direction** requires a **force** to have been exerted on them by the container. 4. This means the particles exert and **equal and opposite force** on the container 5. These **forces over an area** exert a pressure. ## Footnote The net force caused by gas pressure is always perpendicular to the surface of the container.

Question 38

# What is Boyle's law?

Answer 38

p1v1 = p2v2 | 1 and 2 refer to the gas in two different situations

Question 39

# What is necessary for Boyle's law?

Answer 39

constant temperature

Question 40

# What is the pressure law?

Answer 40

If we increase the **temperature** of a **fixed volume of a gas** we **increase** the pressure.

Question 41

What is the atmospheric pressure at the ground?

Answer 41

roughly 1 x 10^5 Pa

Question 42

What happens to air pressure as height changes?

Answer 42

as you **increase** in height there is **less** air above you, which means the air pressure **decreases** | (and vice versa)

Question 43

What is 0K in °C?

Answer 43

-273°C

Question 44

# What is absolute zero?

Answer 44

where the particles have **no kinetic energy** and so are **not moving** and exert **no** pressure

Question 45

# Define work.

Answer 45

the transfer of energy by a force