# The Effect Of Isaac Newton's Laws Of Motion

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Isaac Newton’s first law states that the real effect of a force is always to change the speed of a body, rather than just set it moving, as was previously thought. It also meant that whenever a body was not acted on by any force, it will keep on moving in a straight line at the same speed. What happens to a body when a force does act on it is given by Newton’s second law which states that the body will accelerate, or change its speed, at a rate that is proportional to the force.

In addition to his laws of motion, Newton discovered a law to describe the force of gravity, which states that every body attracts every other body with a force that is proportional to the mass of each body. Thus the force between two bodies would be twice as strong if one of the bodies (say, body A) had its mass doubled. This is what you might expect because one could think of new body A as being made of two bodies with the original mass. Thus the total force between both bodies, say body A and body B, would be twice the original force. And, if say one had twice the mass and the other three times the mass, then the force would be six times as strong. One can now see why all bodies fall at the same rate: a body of twice the weight will have twice the force of gravity pulling it down, but it will also have twice the mass. According to Newton’s second law, these two effects will exactly cancel each other out, so the rate of acceleration will be the same in all cases.

Newton’s laws of gravity