To understand the concepts behind building a life-size rocket car by building a smaller version with popsicle stick frames and film canister cap wheels. These little rocket cars are equipped with a small CO₂ cartridge for an engine and are guided along a fishing line as they reach speeds up to 70 km/h.

This futuristic car needed a sleek aerodynamic body and a scoop-shaped fin to prevent it from leaving the ground. At high speeds, a low pressure zone (fast air) can be created at the top of a car coupled with a high pressure zone (slow air) under the body of a car causing the car to take flight. This phenomenon is better known as Bernoulli's Principle.

Any rocket car trying to break the sound barrier has to be carefully engineered to reduce all friction. Friction is the force opposing the movement of a body by something from the outside environment. In a rocket car, friction can be found within the bearings of its wheels and axle, at the contact point between the tires and the ground, and upon the body of the car caused by air resistance.

• 1 wooden shish cabob skewer
• 4 film canister caps
• 2 large straws
• 1/4 bottle of white glue
• one 7 x 15 cm piece of paper
• 1 CO₂ cartridge, 19 mm diameter
• popsicle sticks

1. The CO₂ cartridge holder: Lay out the strip of paper.
2. Spread glue on half of the paper. Using the CO₂ cartridge, roll the paper into a tube, starting at the end with no glue. Keep the paper tight and make sure it does not stick to the CO₂ cartridge.

3. Place a small bead of glue along the final seam to ensure it is completely sealed. Pinch the paper tight over the rounded end of the CO₂ cartridge and glue down the pinched end. Remove the CO₂ cartridge.

4. The wheel assembly: Cut the wooden skewer and one of the straws into halves.
5. Glue each straw half to 2 separate popsicle sticks and allow to dry.
6. Using the sharp end of the skewer poke holes in the centre of the four film canister caps.
7. Push the skewer piece through the hole in one of the film canister caps. Thread the free end of the skewer through one of the glued straws. Put the other film canister cap on the free end of the skewer and you will then have two sets of wheels for your car.
8. It is important for launching that the centre of the CO₂ cartridge be 3 cm from the ground. This is easily done by attaching the paper CO₂ cartridge holder to the popsicle stick on the wheel assembly.

9. The body and the frame: Next you should design a frame of popsicle sticks abiding by the following constraints:
   • the car must be less than 15 cm wide
   • the CO₂ cartridge must be the piece the farthest to the back of the car
   • the CO₂ cartridge holder must be tightly secured (encased in popsicle sticks)
   • The final straw must be used as a runner for the guide wire and secured to the underbody of the car as low to the ground as possible

The figure below is an example of a simple frame to build.

The starter

Materials listed correspond to their number and are found in the figures below.

1. two 2" x 4", 35 cm long
2. two 1" angle irons 7 cm long

3. two 3/4" diameter steel bars 6 cm long

4. one 1" x 4", 35 cm long

5. one 3/4" steel bar 12 cm long

6. two 1" angle irons 15 cm long

7. one 1" steel bar 6 cm long

8. one 1" steel bar 9 cm long

9. one 1" angle iron 28 cm long
10. two 3/4" bar 38 cm long

11. two 1" angle irons 7 cm long

12. one 2" x 4", 35 cm long
13. two large eyelet screws with bolts
14. one small spring cut to desired tension
15. one 1/4" diameter steel bar 38 cm long

16. two 1/8" diameter steel nail sharpened
17. two small springs to cover 1/4" of each nail
18. two small wires for nail cotter pins
19. twenty-two 3/4" wood screws
20. two small washers for release mechanism
21. four 2" wood screws
22. two small cotter pins

The finish

1. two wood pieces 1" by 2" cut 90 cm long
2. two 2" x 4" cut 35 cm long
3. two 1" x 4" cut 45 cm long
4. twelve 2" wood screws
5. 200' of 40 pound test fishing line

Put together the launcher as shown in Figure 2 & 3. Parts 7, 8, 9, and 15 are all welded to each other. The angle iron used for part number 9 should strike both nails simultaneously to allow for an equal start in each lane. The eyelet screws are used to attach the fishing line and for fine adjustments in the tension. The spring should be tight to allow the arm to strike the nails at a large enough speed to puncture the CO₂ cartridge. Parts 5 and 7 combine to create a starting lever for when the hammer is cocked and the spring is stretched. The steel bars (part 8) are mounted on the back of the starter so that it can be fastened under a door to remain stable. The finish also needs to be weighted down to keep the guide line taut.

Extra Info:

• keep some sandpaper handy to sharpen the nails between rounds
• the person launching the cars should hold on to the CO₂ canister when the launch is taking place to ensure that a large enough hole is punctured
• keep the guide line tight to prevent cars from crossing tracks
• before launch the straw used for a guide wire will need to be sliced down the middle in order to allow the guide wire to slide in; once the wire is in, tape the straw shut for safety
• safety goggles should be worn by the launcher
• caution posters should be laid along the track to avoid tripping over the guide wires

You can see the effects of Newton's Third Law all around you. For one thing, it explains the motion of rockets; the hot gas coming down out of the rocket exerts an equal but opposite force on the rocket, propelling it upward. But Newton's Third Law also explains more everyday events. When you lean against a wall, the reason you don't fall over has to do with Newton's Third Law. Your body pushes sideways against the wall. According to Newton's Third Law, the wall pushes back with a force equal and opposite. This force from the wall is what holds you up.