Balloon Car

Before you begin the activity, clear an open space on a hard surface to test drive the balloon car. Next, prepare a workspace with a cutting board or piece of cardboard to protect the table or counter as you build the car. In this activity, you will use a push pin and sharp scissors. For safety purposes, you may want to perform those tasks yourself or closely monitor your child as they do them. Remove the push pin and scissors from the work area as soon as you finish with them.

Introduce the activity. You can say, “We are going to make a toy car that gets its energy to move from a balloon. 

“How do you think we can use a balloon to make a car move?” Talk with your child about how the balloon could make the car move. Talk about what might happen if they blow up the balloon and attach it to the car.

Spend some time talking about energy. “When you blow up a balloon, the air inside stretches the rubber of the balloon. The air and the stretched rubber become potential energy. Potential energy is the energy stored in an object. A balloon without air has no potential energy. A blown-up balloon has potential energy. Potential energy is probably going to turn into a form of energy like kinetic energy. Kinetic energy is the energy of motion or movement.” 

“Potential (stored) energy and kinetic (moving) energy make mechanical energy. We can use mechanical energy to power the car we build. What happens when you blow up a balloon and let go of it? Try it!” Discuss how the balloon moves and what happens to the air inside the balloon. You can say, “The potential energy of air and stretched rubber turns into kinetic energy when you let go of the balloon and that makes it zip across the room.

“Let’s build a toy car and watch how the potential energy in the balloon turns into kinetic energy and moves the car to make mechanical energy.”

1. Cut an X in the side of the bottle halfway between the mouth and the bottom by lightly pinching either side of the bottle to raise the plastic. Snip a small X the size of the opening of your straw into the plastic using the tips of a sharp pair of scissors.
2. Make the wheels. You or your child can poke holes in each bottle cap by carefully poking the push pin into the center of each bottle cap. Twist the pin around to make the hole a little bit bigger. Use the pointed side of a wooden skewer to slowly twist and poke through the hole so that the skewer fits snugly in the cap. Remove the skewer and repeat on the back side of the cap. Repeat for each bottle cap.
3. Make the axles. First, have your child cut one straw in half to make two pieces of equal length, making sure that each piece is slightly wider than the bottle. Have your child position the bottle so that the hole you cut in Step 1 is facing down. Tape each half of the straw crosswise on the bottom, one at the front and the other at the back. Next, assist your child in cutting both skewers in half. Have your child insert one skewer, pointed tip first, through the straw. Then, slide the wheels on each side so that they are close but not touching the straw. Cut off the ends of the skewers so that they extend past the wheel about the length of the push pin. Repeat with the second skewer.

 

(view from bottom)

4. Finish the car. Your child can flip the car on its wheels and check to make sure it rolls. See Tips for problem-solving ideas.

5. Attach the balloon to the other straw with a rubber band or tape. Test that the balloon is secured to the straw and can take in air by blowing it up partway. You should also be able to pinch off the balloon above the straw inside of it.

6. Gently release the air and stick the open end of the straw through the hole at the top of the bottle down to the mouth of the bottle. The straw should only extend a bit past the mouth of the bottle to allow for blowing up the balloon. Trim the straw a little if it touches the ground. Tape the straw in place near the mouth of the bottle. The tape should not block airflow in or out.

7. Pick up the car and gently hold onto the straw as you blow the balloon up. Hold your finger over the tip of the straw to keep air from escaping. Set the car on the surface and remove your finger from the straw. The car is ready to roll!

(view from top)

Have your child blow up the balloon and hold a finger over the straw or pinch the balloon to hold the air in place. Have them put the car on the ground and then let go! Talk about what happens and have your child write it down in their science journal. Allow your child to race the car multiple times. Do they notice any patterns?

Ask your child questions like: What would happen if you blow the balloon up more or less? Have your child try both ways and write what happens in their science journal. Continue to discuss changes they can make and what the result might be and then try them out. What if they use a thicker straw?, a smaller or bigger balloon?, bigger or smaller bottle caps?