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Newton's Laws of MotionThere was this fellow in England named Sir Isaac Newton. A little bit stuffy, bad hair, but quite an intelligent guy. He worked on developing calculus and physics at the same time. During his work, he came up with the three basic ideas that are applied to the physics of most motion (NOT modern physics). The ideas have been tested and proved so many times over the years that scientists now call them Newton's Three Laws of Motion.First Law
The first law says that an object at rest tends to stay at rest. An object in motion tends to stay in motion, in the same direction and speed. If nothing is happening to you and nothing does happen you will never go anywhere. If you're going in a specific direction, unless something happens to you, you will always go in that direction. Forever.
You can see good examples of this idea when you see video footage of astronauts. Have you ever noticed that their tools float? They can just place them in space and they stay in one place. There are very few forces acting on objects in space. When you put something in one place, it will only move very slowly when gravity pulls it. The sameis true when they throw objects for the camera. Those objects move in a straight line. If they threw something when doing a spacewalk, that object would continue moving in the same direction and speed all time (until a planet's gravity pulled on it). Second Law
The second law says that the acceleration of an object produced by an applied force is directly proportional to the magnitude of the force, the same direction as the force, and inversely proportional to the mass of the object. The second law shows that acceleration and mass are inversely proportional. Inversely proportional means that if one value goes up the other value will go down, assuming everything else stays the same. The equation for this idea is F = m * a.
If you want the force of an effort to stay the same, you need to consider both the mass and acceleration. If you want a constant force but the acceleration is increasing, you will need to lose mass. On the other hand, if the mass of your object increases, you will need it to slow down to keep the same force. Third Law
The third law says that for every action there is an equal and opposite reaction. Forces are found in pairs. Think about the time you sit in a chair. Your body exerts a force moving down and that chair needs to exert an equal force up or the chair will collapse. It's an issue of symmetry. Acting forces encounter other forces in the opposite direction. There's also the example of the shooting cannonball. When the cannonball is fired through the air (by the explosion), the cannon is pushed back. The force pushing the ball out was equal to the force pushing the cannon back. That example is similar to the kick when a gun is fired.
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Go for site help or list of physics topics at the site map!©copyright 1997-2007 Andrew Rader Studios, All rights reserved. Current Page: Physics4Kids.com | Motion | Laws of Motion |
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