Method 1. Blow up a balloon. Hold it closed but do not tie it (a bag clip works well to keep the balloon sealed until the race begins).
2. Stick the balloon onto a drinking straw. 3. Use the card and spare straws to make any further modifications to the balloon rocket that might increase its speed.
4. Thread the string through the straw. 5. Stretch the string across the classroom. 6. Release the neck of the balloon and allow it to travel along the string. 7. By setting up several strings of the same length across the classroom it is possible to race the rockets.
Question Look at the design of the fastest and slowest balloon rockets. What variables do you think might have affected the speed at which the rockets travelled?
Newton’s third law states that for every action there is an equal but opposite reaction. In the case of the balloon rocket in Fig. 9 above, the air was pushed out of the balloon in one direction, causing an equal but opposite force to push the balloon forward in the opposite direction. If two people of the same mass are standing on roller skates and one pushes the other, they will
both roll away from each other. Another way to show this is to hook two spring balances together. Pull on one and observe the readings on both scales. Are the forces the same?
Fig. 10 The illustration shows that for every action there is an equal but opposite reaction. 319
