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Newton's Three Laws of Motion and Basic Rocketry (page 2)

By Pearson Allyn Bacon Prentice Hall
Updated on Nov 18, 2010

What F = MA tells us is that if I have an object such as a golf ball and I act on it with a force such as a golf club, the ball will be accelerated. If I apply a greater force the next time I hit it, the ball will have greater acceleration and travel even farther than it did the first time. (Interestingly, if we didn’t have friction, in this case the air and gravity, our golf ball would continue forever because of its inertia.)

The mass of the object also plays a role. If instead of hitting a golf ball, we placed a baseball on our tee, the baseball would not be accelerated as much and travel as far because the mass of the baseball is greater than the mass of the golf ball.

Newton’s Third Law of Motion: For every action, there is an opposite and equal reaction.

We see the effect of Newton’s third law when we watch a hamster on an exercise wheel. The hamster is trying to run forward, but the wheel under him travels backward.

We normally relate Newton’s third law to projectiles such as bullets, cannons, and rockets. When a cannon is fired, the cannon ball is projected forward, but there is an opposite and equal reaction of the cannon itself rolling backward. Because the cannon has a much greater mass than the cannon ball, it does not travel as far as the cannon ball. When we shoot a rifle, we refer to the opposite and equal reaction as kickback.