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Push a little piston gently. Can the oil lift a heavy crate?
Hydraulics lab · Last updated: 16 October 2026
Push a little piston gently. Can the oil lift a heavy crate? In this 3D lab, you use a small piston to drive a large one and see a small push turn into a big lift. It explains car brakes, digger arms, lifts in garages and the jacks used to raise heavy vehicles.
What you'll discover
- Pressure pushed into an enclosed liquid spreads equally through all of it.
- Because the big piston has a larger area, the same pressure gives it a much larger force.
- The trade-off is distance: the small piston must move a long way to raise the big one a little.
The science in plain words
Pressure is force divided by the area it acts on. Liquids such as oil are almost impossible to squash, so when you push on a liquid trapped in a closed system, the pressure you create is passed on equally to every part of it. This idea is known as Pascal's principle, after the French scientist Blaise Pascal.
In a simple hydraulic machine, a narrow cylinder with a small piston is connected by a pipe to a wide cylinder with a large piston. Pushing the small piston raises the pressure in the oil. That same pressure acts on the large piston, but because its area is much bigger, the total force on it is much bigger too. If the large piston has fifty times the area of the small one, it pushes with fifty times the force, enough to lift a load far heavier than the push you applied.
There is a price to pay. The volume of oil pushed out of the small cylinder must equal the volume that enters the large one, so the small piston must travel fifty times as far as the large piston rises. The work done stays the same, as energy is conserved. Oil is used because it barely compresses, lubricates moving parts and does not rust the metal. Hydraulics power car brakes, excavators, aircraft controls, dentists' chairs and garage lifts.
Where it fits
Common questions
How does a hydraulic jack lift a car?
Pumping the handle pushes a small piston into oil, raising its pressure. That pressure acts on a much larger piston, and because pressure times area equals force, the large piston pushes with a much bigger force. Many small pumps add up to lift the car a little at a time.
What is Pascal's principle?
Pascal's principle says that pressure applied to a liquid in a closed container is passed on equally to every part of the liquid and to the container walls. It is the reason a small push on a small piston can produce a large force on a large piston.
Why do hydraulic systems use oil instead of water?
Oil, like water, hardly compresses, so it passes pressure on reliably. Unlike water, it lubricates moving parts, does not rust steel and works over a wider range of temperatures without turning solid or boiling. Special hydraulic oils are designed for these jobs.
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- Gear Mechanisms: Big gear, small gear: which one turns faster, and why?
- Gas Laws: Squash a gas with a piston, or heat it: how does its volume change?
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Try it yourself
The Hydraulics lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.