Technologies K–10 · Years 7–8

Syringe hydraulics: trading distance for force

Engineering Technologies and Systems focus area (NSW Technology 7–8, 2023); Design and Technologies: Knowledge and understanding, Technologies context: Engineering principles and systems (ACARA v9)

Practical, model not builtLow risk

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

A liquid in a closed system passes pressure on, so a small piston driving a large one multiplies force by the ratio of their areas while the large piston moves less by the same ratio.

What you need

2 × 5 mL and 2 × 20 mL plastic syringes without needles, all from the same brand
50 cm of clear PVC tubing that fits the syringe tips
Water with a drop of food colouring; paper towel
Ruler; 200 g slotted mass
Materials for a hydraulic arm: pine strips, split pins, cable ties

How to do it

Measure each syringe's scale length for its full volume and work out the plunger area: area = volume ÷ scale length.
Fill a 5 mL syringe, the tube and a 20 mL syringe with water, with no air bubbles and the 20 mL plunger at 0.
Push the 5 mL plunger in by 5.0 mL and read how far the 20 mL plunger moves out.
Stand the 200 g mass on the 20 mL plunger and feel the push needed on the 5 mL plunger; then swap so the 20 mL syringe drives and compare.
Repeat the volume test with air in the system instead of water and compare.
Use the results to choose syringe sizes for each joint of a hydraulic arm that lifts an empty drink can.

What you should see

Pushing in 5.0 mL moves the 20 mL plunger to its 5.0 mL mark (water barely compresses), within one graduation of the scale. The force multiplies by area of the large plunger ÷ area of the small one, and the large plunger moves less by the same factor, so force × distance is the same on both sides apart from friction. For example, a 5 mL syringe whose scale is 40 mm long (125 mm²) driving a 20 mL syringe whose scale is 60 mm long (333 mm²) multiplies force by 2.67. With air, the output moves less and springs back, because air compresses. The learner knows it worked when the water system moves the output to the predicted mark and the effort feels smaller when the small syringe drives.

What changes

What you change: the driving syringe (small or large) and the fluid (water or air)
What you measure: output plunger position (mL mark) and effort needed
What you keep the same: the same tubing
the same load
no air bubbles in the water tests

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Hydraulics create extra energy (force goes up but distance goes down by the same factor).
Air works as well as water (air compresses, so some of the push is lost).
The bigger syringe always pushes harder (it depends on which syringe drives and which is driven).

Safety card

Low riskLearners carry it out

Hazards

Water squirting into eyes
Spills near electrical equipment

Controls

Syringes without needles only; safety glasses; tubing pushed firmly onto tips
Work over trays away from computers

Note

No heat or hazardous chemicals (food colouring only). Record the activity on RiskAssess (riskassess.com.au).

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Technology 7–8 Syllabus (2023), NESA. Current: taught from 2026. Code read from the outcomes page on 2026-09-22.TE4-MSC-01
Technology Mandatory 7–8 Syllabus (2017), NESA. Outgoing: replaced by the Technology 7–8 Syllabus (2023) from 2026 and not available after December 2027. Code read from the official syllabus document (DOCX) on 2026-09-22.TE4-8EN
Australian Curriculum v9AC9TDE8K03AC9TDE8K06AC9TDE8P01

Sources

The pages the author read to write this activity.

All Concept Studio activities