What it shows
Pushing a liquid in a closed system passes the pressure on equally in every direction, so a small push at one syringe moves the arm at another. It is the idea behind brakes and JCBs.
The science
Liquids cannot be compressed, so pressure applied at one place is passed on equally in all directions (Pascal’s law). A syringe connected to another by a tube turns the pushing of one plunger into the pushing of the other. If the second syringe has a larger piston, the force is larger but the movement is smaller, which is how hydraulic jacks lift cars.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Four new 10 ml syringes (without needles, from a medical shop)
- One new 20 ml syringe for the force test
- Two metres of clear tube that fits the syringe tips
- Water with a drop of food colour
- Cardboard and ice-cream sticks
- Hot glue or fevicol
- Split pins and a base board
Safety
For this project: Use only new syringes without needles and never use a used syringe. An adult must use the glue gun and cut the cardboard.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Cut cardboard arm parts and join them with split pins at the elbow.
Fix a syringe along the arm with its plunger attached to the moving part.
Connect it with tube to a second syringe on the base used as the controller.
Fill both syringes and the tube with coloured water without air bubbles.
Push the control plunger and watch the arm move.
Make a second joint with another pair of syringes to control a gripper.
Pick up a light object such as a sponge cube.
Replace the syringe on the arm with the 20 ml one, keep the 10 ml one as the controller, and see how the force and distance change.
What you should see
The arm lifts and lowers with the push of a plunger; with a larger piston the arm moves less but lifts a heavier load.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What law is used?
Pascal’s law.
02Why must there be no air bubbles?
Air is compressible and wastes the push.
03Where is hydraulics used in real life?
In car brakes, JCB machines and lifts.
04What happens with a bigger output piston?
More force but less distance.
Take it further
Measure the load lifted using a 10 ml syringe versus a 20 ml one.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Physics Working Models Explained
Twenty classic models, how each works and how to make it
Science projects
Mini and Major Project Guide
For diploma and BTech students: choose, plan, build, document and present
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