Engineering activity
Mousetrap Vehicle
Build a car that moves when you let go of a wound-up clothespin! Explore how a spring stores energy to make things go.
Materials and setup
- clothespin or binder clip
- cardboard
- straws
- string
- bottle caps
- tape
How this changes by age
Pre-K (ages 3–4)
Build a car that moves when you let go of a wound-up clothespin! Explore how a spring stores energy to make things go.
Steps
- Tape a clothespin to a small cardboard car body with straw axles and bottle cap wheels.
- Tie a string from the clothespin jaw to the rear axle.
- Open the clothespin and wind the string around the axle by rolling the car backward.
- Let go of the clothespin. Does the car move forward as the spring pulls the string?
- Try again with more wind-up. Does the car go farther?
- Tell a grown-up one thing that surprised you.
Learning objectives
- Discover that springs store energy that can be released to create motion
- Build a simple vehicle with moving parts
- Observe the relationship between winding and distance
Kindergarten (ages 5–6)
Build a clothespin-powered car and race it! Experiment with wheel size and string length to make it go farther.
Steps
- Build a car base from cardboard with straw axles and round wheels (CDs or cardboard circles).
- Attach a clothespin to the front of the car with rubber bands or tape.
- Tie string from the clothespin to the rear axle. Wind by rolling backward.
- Race your car! Measure the distance it travels.
- Experiment: try longer string (more winds). Does it go farther?
- Try bigger wheels vs smaller wheels. Record which combination gives the most distance.
- Tell a grown-up one thing that surprised you.
Learning objectives
- Build a spring-powered vehicle with adjustable components
- Test how string length and wheel size affect vehicle distance
- Measure and compare distances across different configurations
Early elementary (ages 6–8)
Engineer a mousetrap-powered vehicle (using a clothespin or binder clip as the spring) optimized for maximum distance. Control variables and test systematically.
Steps
- Build a lightweight car frame from cardboard or foam board. Minimize weight.
- Use a strong binder clip as the spring mechanism. Attach string to the clip lever and rear axle.
- Test 1: Different string lengths (short, medium, long). Record distance for each (3 trials).
- Test 2: Different wheel sizes using the best string length. Record distances.
- Test 3: Different surfaces (tile, carpet, wood). Record distances.
- Calculate average distance for each test. Create a data table showing all results.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Optimize a spring-powered vehicle through controlled variable testing
- Calculate averages from multiple trial runs
- Identify which variables most significantly affect vehicle performance
Upper elementary (ages 8–10)
Design a mousetrap vehicle optimized for either maximum distance or maximum speed. Analyze the energy conversion chain and calculate efficiency.
Steps
- Research mousetrap car physics: spring potential energy, string mechanics, friction, wheel diameter effects.
- Choose an optimization goal: maximum distance OR maximum speed (they require different designs!).
- For distance: large wheels, long string lever arm, lightweight frame.
- For speed: small wheels, short string, maximize initial force transfer.
- Build, test, and measure. Calculate approximate energy stored in the spring.
- Estimate energy delivered to wheels based on distance and friction. Calculate efficiency percentage.
- Write a report explaining the physics behind your design choices and the energy conversion chain.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Analyze the complete energy conversion chain in a spring-powered vehicle
- Make design trade-offs between competing optimization goals (distance vs speed)
- Calculate energy efficiency and identify sources of energy loss
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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