Make a Water Racer at Home

Materials you'll need

• 3 CDs (2 large for rear wheels, 1 smaller for front wheel)
• 10 plastic bottle caps
• 6 craft sticks (popsicle sticks)
• 1 straw
• 2 bamboo skewers
• 1 plastic bottle (top half)
• Hot glue gun and glue
• Scissors
• Toothpick or sharp skewer tip for poking holes

 

Step-by-step tutorial

Step 1: Gather your CDs and bottle caps. Using a toothpick or the sharp tip of a skewer, poke a small hole through the center of each bottle cap. These will be your axle holes.

Step 2: Hot-glue one bottle cap (hole side up) to the center of each of your two large CDs for the rear wheels, and glue one cap to your smaller CD for the front wheel. For the front wheel, stack and glue two caps together rim-to-rim for extra width, then attach them to the CD. Let everything dry.

Step 3: Make the water wheel by arranging 6 bottle caps in a pinwheel shape around a central hub — three pairs of caps facing opposite directions, evenly spaced like paddles. Hot-glue them firmly together. This is what falling water will spin.

Step 4: Get your craft sticks and straw. Cut the straw into short sections to use as spacers. Arrange and glue your craft sticks into a rectangular frame: two sticks running lengthwise as side rails, with crossbar sticks at the front, back, and middle. Let the glue set.

Step 5: Thread a bamboo skewer through one rear CD wheel, across through the straw spacers and frame, and out the other side into the second rear CD wheel. Thread the water wheel onto the same rear skewer so it sits centered in the middle of the frame, between the two side rails.

Step 6: Attach the front wheel: thread a second skewer through the front axle straw and into the front CD wheel. Make sure all wheels spin freely and don't glue the skewers to the frame.

Step 7: Cut the top off a plastic bottle to create an open funnel shape. Hot-glue this bottle funnel upright onto the center of your craft stick frame, positioned directly above the water wheel, with the wide opening facing up. This is your water reservoir.

Step 8: Glue a paper car body over the frame and decorate your racer! Add a character, a racing number flag, or whatever you like.

Step 9: Head outside and race! Pour water from a bottle into the funnel. The water flows down onto the paddle caps, spins the water wheel, turns the rear axle, and sends your car rolling forward. The faster you pour, the faster it goes!

Learn more

This car runs on the same idea that powered ancient mills and modern dams: a water wheel. When water falls onto the angled bottle-cap paddles, gravity pulls it down and pushes against each paddle in turn, making the wheel spin — this is called torque, or turning force. Because the water wheel shares a skewer axle with the rear CD wheels, that spinning motion transfers directly through to the wheels, pushing the car forward. The same basic principle powers hydroelectric dams, where falling water spins giant turbines to generate electricity for entire cities.