Engineering activity
Prosthetic Hand
Make a cardboard hand with fingers that move when you pull strings! Discover how your own fingers work with tendons.
Materials and setup
- cardboard
- straws
- string
- rubber bands
- tape
- scissors
How this changes by age
Pre-K (ages 3–4)
Make a cardboard hand with fingers that move when you pull strings! Discover how your own fingers work with tendons.
Steps
- Trace your hand on cardboard. Parent helps cut it out.
- Draw lines on each finger where the joints are (two lines per finger).
- Fold the fingers at the joint lines so they can bend.
- Tape a string to each fingertip. Run the strings down the palm.
- Pull the strings to make the fingers curl! Just like how tendons work in your real hand.
- Tell a grown-up one thing that surprised you.
Learning objectives
- Discover that strings (tendons) can make fingers bend
- Observe how joints allow movement in specific directions
- Connect a mechanical model to how their own body works
Kindergarten (ages 5–6)
Build a mechanical hand from cardboard with jointed fingers and string tendons. Make it grip a ball or pick up a cup!
Steps
- Trace your hand on stiff cardboard and cut it out.
- Score (don't cut through) lines at each finger joint. Fold to create bending joints.
- Tape straws to the back of each finger as guides for the strings.
- Thread a string through each straw and tape it to the fingertip.
- Pull all strings together to make a fist. Can you grip a small ball?
- Try picking up different objects: a cup, a marker, a cotton ball. Which is hardest?
- Tell a grown-up one thing that surprised you.
Learning objectives
- Build a working tendon-and-joint mechanical hand
- Understand how tendons and joints work together for gripping
- Test grip capability on objects of different sizes and weights
Early elementary (ages 6–8)
Engineer a prosthetic hand that can perform specific tasks: grip a cup, pick up a pencil, and turn a doorknob. Optimize for grip strength and dexterity.
Steps
- Build a hand with articulated fingers using cardboard, straws, and strings.
- Add rubber band 'tendons' on the back of each finger to make them spring open automatically.
- Test Task 1: Grip and hold a cup for 5 seconds. Pass or fail?
- Test Task 2: Pick up a pencil from a table. Pass or fail?
- Test Task 3: Turn a doorknob (or jar lid). Pass or fail?
- For each failed task, identify what went wrong and redesign. Test again.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Design a mechanical hand to perform specific real-world tasks
- Understand the role of both flexor and extensor tendons in hand function
- Apply iterative design to solve specific functional challenges
Upper elementary (ages 8–10)
Design a prosthetic hand with individually controllable fingers, opposing thumb, and grip force measurement. Research real prosthetic engineering challenges.
Steps
- Research prosthetic hand design: passive vs active, body-powered vs electric, tendon routing.
- Design a hand with an opposing thumb that can touch each fingertip (key for gripping).
- Build with individual string controls for each finger and rubber band return springs.
- Create a grip force test: how many coins stacked can the hand lift without dropping?
- Test precision grip (pinch a coin), power grip (hold a bottle), and hook grip (carry a bag handle).
- Research the challenges real prosthetic users face. How does your design address or fail at those challenges?
- Write a design report including diagrams, test results, and proposed improvements.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Design a biomechanical system modeling real human hand function
- Test and categorize different grip types and their mechanical requirements
- Analyze engineering challenges in real prosthetic design and propose solutions
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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