Experiment & parent guide

How does hydraulics trade force for distance?

Build a lifting platform, connect the pump and lift a car. Then change one part and observe the difference.

What you can build in this workshop

The pump pressurises the enclosed liquid. Pressure acts on the lifting piston. A larger piston area produces more force at the same pressure, but needs more liquid to move the same distance. Gaining force costs pump travel.

Follow the three steps: build a platform, connect the pump and pump. More machines are available below.

Four research missions

1 · Lift the car

Lift the 900 kg car at least 8 cm with one platform.

Build a lifting platform and connect the pump. The prepared parts already suit the car.
Start “Test 15 strokes” or pump individually. Read the lifting height.
Reach at least 8 cm. Then change only the pump or lifting piston and compare.

A small pump area can act on a larger lifting area through liquid pressure. You gain force and pay for it with more pump travel.

2 · Force and travel

Enlarge only lifting piston A: compare force and height after the same number of strokes.

Test the prepared build for 15 strokes and select “Save A”.
Enlarge only lifting piston A. Keep the load, pump, pump travel and force limit unchanged.
Test another 15 strokes. Compare the required force and lifting height.

A larger piston area needs less pressure and pump force for the same load. The same volume of liquid lifts that larger piston a shorter distance.

3 · Two pistons

Build two connected platforms and lift only piston A first.

Connect the two prepared platforms to the pump.
Close valve B and leave valve A open. Pump and watch both heights.
Check that A rises while B stays at zero. Then open B and close A.

A closed branch valve blocks that liquid path and holds its height. With both branches open, the cylinder requiring less pressure moves first.

4 · Heavy load

Lift the 1,400 kg van at least 2 cm using no more than 500 N of pump force.

Check that the load is 1,400 kg and the available force is at most 500 N.
Change a piston: a smaller pump or a larger lifting piston can reduce the required hand force.
Test and read the load height. With the crane arm, load travel differs from cylinder travel.

Piston areas and the crane arm change force and travel together. A longer load arm moves farther but needs more cylinder force. The machine does not create energy.

Build and test your idea

Understanding the readings

Lifting height · cm

How far the load has risen. The crane arm moves the load a different distance from the cylinder.

Pressure · bar

Pressure is force per area. The liquid transmits pressure from the pump to a connected lifting piston.

Required pump force · N

Hand force needed with this load and these pistons. Your available force must be sufficient.

Pump strokes

How many times you pumped. Failed attempts also count, even though the load does not rise.

Getting started together

Build a platform, connect the pump and pump once. The prepared parts fit the car, so no size or force adjustment is needed first. Quick buttons change loads, cylinders and pumps. Crane arm, two platforms and fine controls are expandable. Change only the lifting cylinder: does it require less force but more strokes? Two branches have independent loads, cylinders and valves. The force setting is an available upper limit, not a command to exert that force continuously. The goal stays in the yellow band; the workbench gives the next step.

Force and distance belong together

Pump force divided by pump area gives the available pressure. At the lifting piston, pressure acts over its area. Ideally, the force ratio equals the area ratio. Doubling diameter quadruples area. The pump must supply the liquid volume corresponding to the chosen lifting height.

What do valves do?

Check valves prevent liquid simply flowing backward on the return pump stroke. A reservoir supplies the next stroke. The visible release valve opens a return path to the reservoir: the load sinks and liquid returns. A disconnected line transmits no new pump pressure to the load.

Two cylinders on one pump

Both cylinders share a pressure circuit but do not automatically move equally. Required load force divided by piston area sets the pressure threshold. In this quasistatic model, the branch with the lower threshold moves first. At equal thresholds, volume divides equally; identical cylinders rise together. A piston at its maximum travel leaves further pump volume for the other branch, if the force is sufficient.

The crane arm

An ideal lever adds to the hydraulic cylinder. The travel ratio is load-arm length divided by cylinder-arm length. A ratio of two doubles load travel for the same cylinder stroke and requires twice the load force at the cylinder. Energy is conserved. The drawing uses an idealised lever with a moving support; joint geometry and side forces are not separately modelled. Cylinder travel and load travel therefore differ.

Steer two platforms

Each branch has a shut-off valve. A closed branch accepts no new pump volume and holds its height. Only open branches descend when the release valve opens. Lift one load, hold it, then move the other. With both branches open, required load force divided by piston area determines where volume flows first.

Compare fairly

Save a trial with the car and change only lifting-piston diameter. Compare required force and height after the same 15 strokes. Predict what becomes easier and what moves less far. Maximum available force and the separately displayed required force are different quantities.

Away from the screen

An adult can gently demonstrate with two tightly connected needle-free plastic syringes and water. Different syringe sizes make the force–distance relationship visible. Use small hand forces only; do not lift people or heavy objects.

Model and limits

The lab calculates piston areas, pressure, volume and work. Pump travel is adjustable from 5 to 25 cm. Motion is slow and quasistatic, with limited pump force, simplified seal friction and pump losses. Fast flow, flexible lines, leakage and air bubbles are not included. The gauge shows active pump-circuit pressure. When blocked, it is limited by available force and pump efficiency. Stroke count includes failed attempts. Disconnected lines transmit no new pressure, while check valves hold already raised loads. The release valve lowers them. Car travel is exaggerated visually; centimetre readings are authoritative. Parallel-branch flow losses and height-dependent pressure differences are omitted. Cylinder travel is limited to 32 cm; a lever may make load travel larger. Energy counts only actual delivered volume and mechanical work. This is not a real lifting-machine design tool.

Keep investigating

Write a prediction, save a finished trial as A, and change one part. Compare at equal stroke counts. Results retain predictions and list changed parts. Mission feedback names conditions to restore; free building remains available.