Hydraulic Lift
How does a garage lift a whole car with one person pumping? Size the two pistons and hold the pump to lift a scooter, a car, or even an elephant, using nothing but oil.
Class 8 Ch 6 · Class 11 FluidsEach pump pushes the small piston down 25 cm.
Try this
0 of 5 doneSet it up so you could lift the car with less than 200 N of push.Hint: make the small piston small and the big piston big
Lift a 4000 kg elephant with less than 500 N.Hint: the area ratio needs to be about 80 or more
Make both pistons the same size. Does it still help?Hint: set both diameters to the same number
Pump the lift all the way to the top.Hint: hold the Pump button. A bigger small piston means fewer pumps
Get the oil pressure above 10 atmospheres.Hint: a heavy load on a narrow big piston
What's happening
Pressure spreads everywhere
Push on a liquid in a closed container and the extra pressure reaches every part of it equally. That's Pascal's law. Pressure is force spread over an area, so the same pressure pushing on a bigger area gives a bigger force.
Small push, big lift
If the big piston has 100 times the area of the small one, it pushes up with 100 times the force. A person's push on the small piston can hold up a car. Doubling the diameter makes the area 4 times bigger, so diameter matters a lot.
But you pump a long way
Oil can't be squashed, so the oil you push out of the small cylinder must fill the big one. The big piston rises only a little for each pump: if it's 100 times the area, it moves 100 times less. The force goes up, the distance goes down, and the work stays the same.
Who figured this out?
Simon Stevin
1586, NetherlandsShowed that the pressure at the bottom of a liquid depends only on its depth, not on the shape of the container: the 'hydrostatic paradox'.
Blaise Pascal
1647–1653, FranceStated that pressure on a confined liquid spreads equally in all directions, and described how a small piston could push a large one: the idea behind every hydraulic machine.
Joseph Bramah
1795, EnglandPatented the hydraulic press, putting Pascal's law to work to squeeze and lift with enormous force.
Learn more
- Pascal's law · Wikipedia
- Hydraulic press · Wikipedia
Check yourself
1. The big piston has 50 times the area of the small one. A 20 N push on the small piston lifts…
2. You double the diameter of the big piston. Its lifting force becomes…
3. Why does a hydraulic lift use oil and not air?
4. Does a hydraulic jack give you free energy?
Common questions
What is Pascal's law?
Pascal's law says that pressure applied to a liquid in a closed container is passed on equally to every part of the liquid and to the walls of the container. It was stated by Blaise Pascal in the 17th century.
How does a hydraulic lift work?
A hydraulic lift has two connected cylinders filled with oil, one narrow and one wide. Pushing down on the small piston creates pressure in the oil. The same pressure acts on the large piston, and because its area is much bigger, it pushes up with a much bigger force, enough to lift a car.
What is the formula for a hydraulic lift?
F₁/A₁ = F₂/A₂, so F₂ = F₁ × (A₂/A₁). Here F₁ is the force on the small piston of area A₁ and F₂ is the force on the large piston of area A₂. The distances moved follow A₁ × d₁ = A₂ × d₂.
How does a hydraulic jack work?
A hydraulic jack uses a small pump piston, worked by a handle, and a large lifting piston. Each stroke of the handle pushes a little oil from a reservoir into the big cylinder through a one-way valve, raising the load a small amount. A release valve lets the oil flow back to lower it.
Where are hydraulic systems used?
Car jacks and garage lifts, hydraulic brakes in cars and motorbikes, JCB excavators and cranes, dentist and barber chairs, aircraft landing gear and the hydraulic presses used to shape metal.
Does a hydraulic lift break the law of conservation of energy?
No. It multiplies force, but the small piston must move a much longer distance than the large piston rises. Work done = force × distance is the same on both sides, ignoring friction.
Ideal lift: oil can't be squashed and there's no friction or leaking. Pressures shown are on top of the air pressure around us.
Play next
All simulationsProjectile Motion
Launch at any angle and speed, then find the angle that throws the farthest.
Forces and Friction
Push, pull and change the surface to see which forces win and why things stop.
Levers and Pulleys
Slide the fulcrum and add pulleys to lift a heavy load with less effort.