Engineering activity
Hydraulic Arm
Make a simple squirting syringe machine! Push water from one syringe into another through a tube and watch the second one move.
Materials and setup
- plastic syringes
- flexible tubing
- cardboard
- paper fasteners
- tape
- water
How this changes by age
Pre-K (ages 3–4)
Make a simple squirting syringe machine! Push water from one syringe into another through a tube and watch the second one move.
Steps
- Get two plastic syringes (no needles) and a piece of flexible tubing.
- Fill one syringe with colored water. Connect both syringes with the tube.
- Push one syringe plunger in. What happens to the other syringe?
- Pull the first plunger back. What happens now?
- Try pushing fast and slow. Does the speed change how the other syringe moves?
- Tell a grown-up one thing that surprised you.
Learning objectives
- Discover that pushing liquid in one place makes it push somewhere else
- Observe that liquid transfers force through a tube
- Explore speed and force relationships with hands-on play
Kindergarten (ages 5–6)
Build a cardboard arm that lifts things using syringes filled with water. Push one syringe to make the arm move up and down!
Steps
- Cut two cardboard strips for the arm and base. Connect them with a paper fastener at the elbow joint.
- Attach one syringe to the base and another to the moving arm with tape.
- Connect both syringes with flexible tubing. Fill the system with water (no air bubbles).
- Push the base syringe. Does the arm lift up?
- Try picking up a small toy by taping a clothespin to the arm tip.
- Draw your hydraulic arm and label: syringes, tube, arm, base, elbow.
- Tell a grown-up one thing that surprised you.
Learning objectives
- Build a working hydraulic mechanism using syringes and tubing
- Understand that liquid pressure can move things at a distance
- Label and identify parts of a simple machine
Early elementary (ages 6–8)
Engineer a hydraulic robotic arm with multiple joints that can pick up and move objects. Use pairs of syringes for each movement direction.
Steps
- Design an arm with at least 2 joints: shoulder (up/down) and elbow (bend/straighten).
- Build the arm structure from cardboard with paper fastener joints.
- Install a syringe pair for each joint — 2 pairs total, each connected with tubing.
- Fill all systems with water, removing air bubbles carefully.
- Add a gripper at the end using a clothespin or binder clip.
- Practice picking up small objects and moving them to a target zone. Time yourself.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Build a multi-joint hydraulic system with independent controls
- Understand that each joint needs its own hydraulic circuit
- Apply hydraulic principles to perform a practical task (pick and place)
Upper elementary (ages 8–10)
Design a multi-axis hydraulic arm with gripper. Explore Pascal's law by using different-sized syringes to multiply force. Calculate mechanical advantage.
Steps
- Research Pascal's law and how hydraulic systems multiply force.
- Design a 3-joint arm: base rotation, shoulder lift, and elbow bend, plus a gripper.
- Experiment: connect a large syringe to a small syringe. Push the large one — what happens to the small one?
- Calculate mechanical advantage: large syringe area divided by small syringe area.
- Build the full arm. Use large-to-small syringe pairs where you need more force (shoulder joint).
- Test by lifting objects of increasing weight. Record the maximum lift capacity.
- Write a report explaining how Pascal's law enables your arm to lift heavy objects.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Apply Pascal's law to calculate hydraulic mechanical advantage
- Design a multi-axis hydraulic system with force multiplication
- Analyze the trade-off between force multiplication and movement distance
Safety and evidence note
Read the full activity before beginning. An adult should supervise tools, heat, food, outdoor work, movement, and experiments as appropriate. Completion records that the activity was done; the child’s explanation, work sample, photo, or demonstration is stronger evidence of learning than a completion check alone.
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