Properties of Matter

Hydraulic machines

Teaching Guidance for 11-14 Supporting Physics Teaching

Pistons and forces

Wrong Track: I push down on this piston and the force goes around the bend and pushes up on the other piston.

Right Lines: The hydraulic fluid is squeezed. So there are more collisions on the bottoms of both pistons. These extra collisions provide forces. The larger the piston the more collisions there are and the bigger the force. The pistons generate forces proportional to their area.

The force does not travel

Thinking about the learning

Some pupils develop a picture of forces being carried, by the fluid, from cylinder to cylinder in a hydraulic machine.

Thinking about the teaching

You need to be careful not to suggest that the force slides around the bend from one piston to another. Instead make the connection via the pressure in the fluid.

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