Hydraulic systems transmit force through fluid — Engineering, 11–13 years
A push on a small piston can create pressure in a trapped liquid and produce a larger push on a wider piston.
Pressure can travel through a liquid
In a hydraulic system, a liquid is sealed inside pipes or cylinders, so it cannot simply escape sideways. Pressing one piston pushes the liquid and creates pressure throughout the connected liquid. That pressure can move another piston, even when the two pistons are far apart.
Why engineers use hydraulics
Machines sometimes need a strong, smooth push in a small space. A hydraulic system can send force through flexible pipes and multiply it with a larger piston. The trade is that the small piston must move farther or more often, and the system must stay sealed.
A hydraulic lift in numbers
A small piston has an area of 2 square centimetres, and a large piston has 20 square centimetres. A 30-newton push creates pressure of 30 ÷ 2 = 15 newtons per square centimetre. The large piston receives 15 × 20 = 300 newtons, ignoring friction.
A larger force means a smaller movement
It is easy to imagine getting a bigger output force for free. The mistake feels natural because the large piston clearly pushes harder. But fluid systems conserve energy approximately: if the output piston has ten times the area, it moves about one tenth as far for the same input movement.
Brakes and lifting machines
Car brakes use hydraulic fluid to carry pressure from the pedal to brake pads near the wheels. Garages use hydraulic lifts to raise cars, and excavators use hydraulic cylinders to move heavy arms. These systems work only when the fluid path has no significant leaks or trapped air.
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