Unit 5: (b) Density and pressure

5.3 What is density?

Density is the mass per unit volume of a substance.

5.3 What is the equation for density?

ρ = m/V.

5.3 What does ρ represent in the density equation?

Density.

5.3 What does m represent in the density equation?

Mass.

5.3 What does V represent in the density equation?

Volume.

5.3 What is the unit of density?

kg/m³.

5.3 What is the unit of mass in the density equation?

kg.

5.3 What is the unit of volume in the density equation?

m³.

5.3 How do you calculate density?

Divide mass by volume.

5.3 How do you calculate mass using density?

m = ρV.

5.3 How do you calculate volume using density?

V = m/ρ.

5.3 What does a high density mean?

A large mass is packed into a small volume.

5.3 What does a low density mean?

A small mass is spread over a large volume.

5.3 If mass increases but volume stays the same, what happens to density?

Density increases.

5.3 If volume increases but mass stays the same, what happens to density?

Density decreases.

5.3 Why do different substances have different densities?

Their particles have different masses and arrangements.

5.4 How do you find the density of a regular solid practically?

Measure its mass, measure its dimensions, calculate volume, then use ρ = m/V.

5.4 How do you measure the mass of an object when finding density?

Use a balance.

5.4 How do you find the volume of a regular solid?

Measure dimensions and use the correct volume equation.

5.4 How do you find the volume of a cube?

Volume = length × width × height.

5.4 How do you find the density of an irregular solid practically?

Measure mass and find volume using water displacement, then use ρ = m/V.

5.4 How is the volume of an irregular object measured?

Use a displacement can or measuring cylinder to measure displaced water.

5.4 How do you investigate the density of a liquid?

Measure the mass and volume of the liquid, then use ρ = m/V.

5.4 Why should measurements be repeated when investigating density?

To improve reliability and calculate an average value.

5.5 What is pressure?

Pressure is the force acting per unit area.

5.5 What is the equation for pressure?

p = F/A.

5.5 What does p represent in the pressure equation?

Pressure.

5.5 What does F represent in the pressure equation?

Force.

5.5 What does A represent in the pressure equation?

Area.

5.5 What is the unit of pressure?

Pascal (Pa).

5.5 What is the unit of force in the pressure equation?

Newton (N).

5.5 What is the unit of area in the pressure equation?

m².

5.5 How do you calculate force using pressure?

F = pA.

5.5 How do you calculate area using pressure?

A = F/p.

5.5 What happens to pressure if force increases and area stays the same?

Pressure increases.

5.5 What happens to pressure if area increases and force stays the same?

Pressure decreases.

5.5 Why do sharp objects produce greater pressure?

They have a smaller area, so the same force creates greater pressure.

5.5 Why do wide tyres reduce pressure on the ground?

They increase the contact area, reducing pressure.

5.6 How does pressure act in a gas or liquid at rest?

Pressure acts equally in all directions.

5.6 Why does pressure act in all directions in a fluid?

Fluid particles move randomly and collide with surfaces in all directions.

5.6 Does pressure in a stationary liquid act only downwards?

No, it acts equally in all directions.

5.7 What is the equation for pressure difference in a liquid?

p = hρg.

5.7 What does p represent in p = hρg?

Pressure difference.

5.7 What does h represent in p = hρg?

Height or depth of liquid.

5.7 What does ρ represent in p = hρg?

Density of the liquid.

5.7 What does g represent in p = hρg?

Gravitational field strength.

5.7 What is the unit of pressure difference?

Pa.

5.7 What is the unit of height in p = hρg?

m.

5.7 What is the unit of density in p = hρg?

kg/m³.

5.7 What is the unit of gravitational field strength in p = hρg?

N/kg.

5.7 What happens to pressure difference when depth increases?

Pressure difference increases.

5.7 What happens to pressure difference when liquid density increases?

Pressure difference increases.

5.7 What happens to pressure difference when gravitational field strength increases?

Pressure difference increases.

5.7 Why is pressure greater deeper in a liquid?

There is more liquid above, so the weight of the liquid is greater.

5.7 What value is usually used for gravitational field strength?

9.8N/kg or approximately 10N/kg.