Motion and Laws of Motion Newtons Third Law of Motion Rockets are used for launching artificial satellites. What is the force Fig. 3.15 that makes a rocket shoot up? Lets make a balloon rocket. Pass a long string through a straw and tie the string between two windows of the classroom as shown in the figure. Paste an inflated balloon on the straw. • Deflate the balloon and release it suddenly. What do you observe? • Isn't the motion of the balloon in a direction opposite to the direction of motion of the air? • Isnt this due to the force produced by the strong release of air? If this force is taken as action, the force that pushes the balloon along the string can be taken as reaction. Lets do another experiment. Fill a boiling tube with some water and close it gently with a cork as shown in the figure. Suspend it from a stand. Heat the boiling tube slowly. What do you observe? • Is it not due to the force exerted on the cork by the steam from the boiling water? • If the force exerted by the steam on the cork is taken as the action, what is the reaction? Write down what the action and the reaction are when you Fig. 3.16 walk on a floor. Gas at high pressure is pushed out from the chambers of a rocket. It is the reaction of this force that propels the rocket forward. • Are action and reaction equal and opposite? Fig. 3.17 55
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