A Balloon Car is usually used to demonstrate Newton's Laws of Motion. I made it because it looked like fun. I've been learning how to babysit my 1-year-old cousin, and it looked like something that would make her laugh,

Step 1: Materials and Supplies

There are a lot of different materials that can be used for different parts of the balloon car. When different items that can be substituted, they will be listed. The item choices used for this project will be in bold.

1. BODY OF CAR

Plastic bottle
Small cardboard box
Small milk carton (size used for school lunches
Medium size plastic cup

2. WHEELS

Small bottle caps from plastic bottles (4)
CD's (4)

3. AXLES

Pencils (3)
Pens (3)
Wooden Skewers (3)
Set of chopsticks broken in half (need two pairs, only keep three of the sticks

4. FLEXIBLE STRAWS (3)

Straws can be plastic or rubber

5. ENERGY SOURCE

Large balloon (round is usually used, but any shape will work)

6. MISCELLANEOUS SUPPLIES - May not need all of them

Rubber band
Tape
Scissors or Hobby
Knife
Paper clips

SAFETY CONCERNS: Since this activity involves punching a hole through plastic with a sharp object, may sure there is an adult nearby

Step 2: Prepare the Body

For this step, the scissors or hobby knife, straws, tape, and plastic bottle will be needed.
Cut two straws so they are a little bit longer than the width of the car. zDepending on the length of the straw, sometimes one straw cut in half can be used.
Tape the straws to one side of the bottle. NOTE: It would be useful to have several pieces of tape already cut and accessible during this process.

Step 3: Prepare the Axles and Wheels

For this step, the pencils, bottle caps, and scissors or hobby knife will be needed.
Using the scissors or hobby knife, put a hole in the middle of each bottle cap. The hole should be just large enough for the pencil to be pushed through. NOTE: Make sure an adult is nearby when the scissors or hobby knife is being used.
On one end of each pencil, push a bottle cap on until it is past the end of the pencil.
Thread each pencil through one of the straws taped to the bottle.
Push bottle caps onto the other ends of the pencils until they are past the end of the pencil.
Check to make sure the axle spins freely. If using a wooden or tile floor, may need to use a carpeted area in order for enough friction to be generated to turn the axles.
Make adjustments as needed.

Step 4: Installing the Energy Source

For this step, a rubber band, a balloon, scissors, tape, and straw will be needed.
Slide one end of the straw into the neck of the balloon.
Tightly wrap a rubber band around the neck of the balloon.
Blow the balloon up through the straw to make sure there are no leaks. If the balloon does not inflate at all, check to make sure the rubber band hasn't collapsed the straw. If this hasn't happened, undo the rubber band enough to allow air to go into the balloon.
Cut a tiny hole in the top of the plastic bottle. It should be big enough for the straw to slide through.
Insert the end of the straw without the balloon through the top of the bottle and put the mouth of the bottle.
Tape the straw so it points backwards, not down.

Step 5: Finish and Troubleshoot

Inflate the balloon. Hold the open end closed while placing it on the floor.
Release the car and it should propel forward.
If the car does not move at all or moves very slowly, inflate the balloon with more air than previously. If it still doesn't move, use a larger balloon.
If the car still does not move, check the axles to make sure they spin freely. Make any adjustments necessary