Newton's+Laws

=Newton's Laws of Motion= www.physics4kids.com

There 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