A force acting upwards due to pressure is an upthrust.

The pressure on a surface is the effect of a force acting over an area.

Depth is the distance under the surface of a liquid.

Atmospheric pressure is the pressure caused by the atmosphere, this decreases with height.

Pressure at different depths and heights

Science

In the Particle explanations of density and pressure unit, pupils will build on this knowledge to learn how the arrangement and movement of particles in solids, liquids and gases explain density, pressure, floating and convection.

In the Forces unit, pupils learnt how to accurately describe and explain the actions of forces in a range of situations.

This unit explores forces, deformation, Hooke’s Law, moments, and work done. It covers pressure in liquids, atmospheric pressure, upthrust, and equilibrium, as well as simple machines and force-extension relationships, highlighting how forces affect motion, friction, and object deformation.

Hidden forces

a force acting upwards due to pressure differences

the effect of a force acting over an area

the distance under the surface of a liquid

the pressure caused by the air in the atmosphere

Match the key words and phrases to the explanations.

Which of these will increase the maximum weight a raft can support before it starts to sink? 

A raft of weight 2000 N and surface area of 4.0 m$$^2$$ floats on the surface of water.  What pressure is the water putting on the raft?

A shark is travelling deeper and deeper into the ocean. Which of the following are correct?

moving from 1000 m under the surface of the ocean to 1000 m above it

moving from 100 m under the surface of the ocean to 1000 m above it

moving from 100 m under the surface of the ocean to the surface (0 m)

moving from the surface of the ocean (0 m) to 1000 m above it

moving from the surface of the ocean (0 m) to 100 m above it

Sort these statements into order of the change in pressure. Start with the one describing the greatest change in pressure to the one describing the smallest change in pressure.

The water has become weightless as the card blocks gravitational forces.

The water pressure pushing down is about zero as the card has a very small area.

Air pressure below the card produces a force greater than the weight of water.

The card is waterproof so the water cannot escape.

A magician fills a glass with water and puts a sheet of card on top. They then turn the glass and card over carefully and the water does not fall out. What is the best explanation for this?

sharpening the knife to decrease the area of contact

making the knife blunt to increase the area of contact

Which of the following will increase the pressure produced by a knife being used to cut a rope?

A raft of weight 400 N floats on the surface of water. What is the size of the upthrust acting on the raft?

Which of these is the correct equation to calculate pressure?

A box with a weight of 30 N touches the floor over an area of 0.5 m$$^2$$. What pressure does the box produce on the floor?

A pupil pushes downwards with their hand which has a surface area of 60 cm$$^2$$. The pressure they produce is 1.2 N/cm$$^2$$. What sized force are they pushing down with?

a force of 1 N acting over an area of 1 cm$$^2$$

a force of 1000 N acting over an area of 1 m$$^2$$

a force of 1 N acting over an area of 1 m$$^2$$

a force of 10 000 N acting over an area of 10 000 cm$$^2$$

a force of 1 N acting over an area of 10 000 cm$$^2$$

Which of the following produces a pressure of one pascal (1 Pa)?

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