produced by the forces from particles within a fluid acting on each other or on a surface

a force acting upwards on an object in a liquid due to pressure differences between the top and bottom surface

the mass per unit volume of a substance; a less dense substance will float on top of a more dense one

Upthrust

Combined science

Calculating density and measuring volume

Measuring density

Pressure in a fluid

Explaining convection

Changes of pressure

In the Energy of moving particles unit, they will build on this knowledge to learn how the movement and nature of different particles transfers energy by conduction, and how specific heat capacity and specific latent heat quantify the effect of heating on the properties of a material.

In the Heating and cooling unit, pupils learnt how the motion of particles in solids, liquids and gases changes when they are heated, how thermal conduction and insulation work and why heating different materials doesn’t always increase their temperatures by the same amount. 

This unit defines density and explores how it varies between states of matter based on atomic arrangement. It covers mass conservation during physical changes, gas behaviour, fluid pressure, buoyancy, and atmospheric pressure, and calculations involving density, mass, and volume relationships.

Particle explanations of density and pressure

Ice is made of heavier particles than water.

The particles move faster in water than in ice.

The particles are farther apart in ice than in water.

Which of the following statements explains why ice floats in liquid water?

At greater depths, the particles are larger.

At greater depths, the particles are heavier.

At greater depths, the particles are closer together.

At greater depths, the particles push on each other with greater forces.

Which of the following statements correctly describe differences for particles of water at greater depths, compared with particles that are not as deep down?

Upthrust is caused by the weight of an object.

Upthrust is caused by differences in pressure in a fluid.

No upthrust acts on an object that is floating on a liquid.

No upthrust acts on an object resting on the bottom of a container of liquid.

Which of the following statements about upthrust is correct?

For an object surrounded by a liquid, how many of the following are possible descriptions of the upthrust force: no upthrust; upwards upthrust; downwards upthrust; upthrust in all directions?

A pupil places an object underwater and sees that it stays where it is, without floating upwards or sinking downwards. The weight of the object is 3 N. What is the upthrust force on the object? 

A toy is dropped in a swimming pool. The toy has a mass of 0.80 kg, a weight of 8.0 N and an upthrust force of 6.0 N acting on it. What is the size and direction of the toy’s vertical acceleration?

Which of the following is a definition of the density of an object?

Which of the following does the symbol $$g$$ represent?

The particles vibrate in fixed positions.

Which of the following statements describe the movement and arrangement of particles in liquids?

If a fluid is compressed, its pressure increases.

A fluid only has pressure where it touches solid objects.

A fluid that is not inside a container does not exert a pressure.

At each point within a fluid, the pressure is equal in all directions.

Which of the following statements are correct?

The pressure in a fluid increases with depth.

The pressure in a fluid increases with height.

The area of the mountain is larger at the bottom than at the top.

The bottom of the mountain has more surface for the air to push on than the top.

Which of the following explains why air pressure is lower at the top of a mountain than it is at the bottom of the mountain?

The pressure is greatest at the top of the water.

The pressure is the same everywhere in the water.

The pressure is the same at all places with equal depth.

The water exerts pressure on the bottom of the container but not on its sides.

The picture shows a cross–section of a container of water. Which of the following statements about the pressure of the water is correct?

Upthrust

Lesson outcome