Engineering at Home: Build a Mousetrap Car

Did you know there are simple and fun crafts you can make to share engineering at home with your kids? Building a mousetrap car is one of those simple crafts, and it’s fun for all ages. Building a mousetrap car is so enjoyable that there are events all over the nation for mousetrap car races!

We know engineers like to take things apart to see how they work, and want to teach their kids the same thing. While a simple mousetrap car may not go very far or very fast, it will show you how stored potential energy becomes kinetic energy.

When you’re finished with this project, you can try building a more complex mousetrap car by changing a few things. Think about what you could do to design the car to go a longer distance and go faster. Consider the wheel-to-axle ratio, inertia, the rate of energy release, and friction — these areas might help get your creative juices flowing for future improvements.

Things to Consider

For a Long-Distance Mousetrap Car:

• Smallest fraction for mechanical advantage
• Reduce friction
• Reduce weight

For a Faster Mousetrap Car:

• Largest fraction for mechanical advantage
• Good traction in rear wheels
• Reduce friction
• Reduce weight
• Reduce rotational inertia

Safety Note

Mouse traps are dangerous. If one snaps back on your hand while you’re holding it, it could cut you, or worse, break your finger. This project requires adult permission and supervision to complete.

Supply List

• 2 pieces of heavy cardboard, 4" x 10" (other dimensions will work, but this is a good place to start)
• 4 DVDs or CDs (recycle old ones, or buy new ones at an office supply store)
• 4 beveled faucet washers, 1/4L (19/32"), found at most hardware or home improvement stores in the plumbing department
• 2 dowels, 3/16" x 6" long (scale up or down if you change your cardboard dimensions)
• 1 dowel, 1/4" x 10" long
• 2 drinking straws
• Masking or duct tape
• Zip ties, an assortment of 4" will work
• String
• Hot glue
• Scissors
• Ruler

Step 1: Build the Body of the Mousetrap Car

Before you begin, visualize your mousetrap car. You’re going to need to create a body that’ll form the frame of your car, wheels, and an engine to power everything.

Cut a rectangular notch about 1" x 2" on one short side of each cardboard piece so that the notches overlap. Place the two pieces of heavy cardboard on top of each other and tape them together, making a double-thick, heavy-duty piece of cardboard. Make sure your notches line up.

Tip: If you’re going for distance and not speed, lighten the load as much as possible by cutting holes in the frame.

Step 2: Prepare the Mouse Trap

Once your cardboard is taped together, attach the straws. Measure the short side and the two sections on either side of the cutout, cut your straws to match these lengths, and hot glue them in place. Be sure the straws are parallel to each other and the leading edge of the cardboard.

While the glue dries, prepare the mousetrap. Remove the small pieces that make up the release trigger — the bait holder and wire bail. Use 2-3 zip ties to secure the 1/4" dowel to the snap arm, reinforcing with tape or hot glue as needed. Make sure the dowel points forward, away from the notch, and lines up with the notch center when pulled back.

Attach a piece of string to the end of the dowel with another zip tie. The string should reach a bit longer than the hook on the rear axle, with a small loop tied at the end.

Step 3: Prepare the Wheels

Put a piece of tape over the hole in the center of each DVD or CD. Turn it over and press a beveled faucet washer into the center, sticking it to the tape, then secure with a generous amount of hot glue. Repeat for all 4 wheels.

Step 4: Add the Axles and Wheels

Once the hot glue has dried, slide the 3/16" dowels into the straws and press a wheel onto each end. If the dowels are difficult to push through, rounding or slightly sharpening the ends can help.

Once all four wheels are attached, do a test run to see if the car rolls straight. If it doesn’t, straighten the straws.

Step 5: Attach the Hook

Attach a 4" zip tie to the center of the car axle exposed by the notch, cut it short (about 1/4 inch) to form the hook for your string, and secure with a dab of hot glue.

Attach the string to the hook, wind it backward, put the car on the ground, and let go — it should start rolling away.

Roll your vehicle several times to test it. If it’s not rolling smoothly or is veering to one side, take some time to adjust it.

Tip: For a more durable car, use lightweight wood instead of heavy cardboard.

How It Works

A set mouse trap is full of potential energy. When released, it gets converted into kinetic or motion energy. Your mousetrap car’s design allows that energy to transfer to the axle to make the wheels turn.

When the mousetrap in your car snapped closed, it yanked the string forward. As the string got pulled, friction between it and the axle caused the axle to rotate, which turned the wheels and moved the car forward.

Hopefully, everyone had a great time putting together their mousetrap car and learning about potential and kinetic energy. Now the mousetrap car makers can build their science fair project, share the ideas with friends, or join the mousetrap car races.