# Physics the first Law of Motion Discovered by Isaac Newton

Newton’s first law of motion was the first of three laws discovered by Sir Isaac Newton. He presented these laws in his book “Principia Mathematica Philosophiae Naturalis” in 1686. The laws of motion describe how objects move. Newton’s first law of motion is also called the law of inertia. Newton’s second law of motion claims that the force of a body is equal to mass times acceleration (F=MA). Newton’s third law of motion claims that the force between two bodies are equal but opposite.

There are two parts to the law. First, it claims a body at rest tends to stay at rest unless acted upon by an outside force. The second part claims that a body in motion tends to continue in motion at the same speed and direction unless acted upon by an outside force (same as first part). The force of the first part disturbs the body at rest so that it moves. The force of the second part slows down, speeds up, or changes the direction of the moving body.

If there is a force pushing a body toward the right that is stronger than a force pushing the body toward the left, then the body will move to the right – the amount of force pushing the body toward the right being greater than the force pushing the body toward the left.

A projectile falling in the atmosphere is an example of Newton’s first law of motion. However, Newton’s first law of motion does not take into account details like the weight of the falling projectile, gravity, wind, or any friction that is present. Friction is a force that takes into account the force caused by one body contacting another. For this reason it is not a fundamental force. The shape of the projectile will also be a factor (a paper airplane will fly off if folded properly). Galileo’s laws of falling bodies that claim that any bodies will fall at the same rate in a vacuum regardless of the weight of the bodies are only true in a vacuum.

A rocket taking off from its launch pad is another example of Newton’s first law of motion. The rocket is in a resting state when it sits on the launch pad. Newton’s first law claims that the rocket will not blast off until the fuel is ignited. When it blasts off, it will remain in motion until acted upon by an outside force. It will slow down because of the effect the force gravity has on it. If it wants to fly to outer space, it will have to travel faster than the escape velocity for the Earth, which is 25,000 miles per hour. In the metric system this is 11.2 kilometers per second.