# Newton's 3 Laws Of Motion

By aaron

Newton's three laws of motion-- usually just called Newton's 3 laws-- are a set of laws put forth by Isaac Newton in his work titled Philosophiæ Naturalis Principia Mathematica, which translates as Mathematical Principles of Natural Philosophy, which was first published in 1687. The laws describe the behavior of objects as forces are applied to them.

## Law 1: The law of inertia

The first law states that an object at rest will stay at rest and an object in motion will stay in motion at a constant velocity unless acted upon by an outside force. This concept is known as inertia.

## Law 2: Force = Mass x Acceleration

The second law states that the force on an object is equal to the mass of the object times the acceleration of the object. Mathematically, this can be simplified into a very elegant equation, which is simply, force equals mass times acceleration.

## Law 3: Equal and opposite reactions

Finally, the third law states that when one object exerts a force on a second object, the second object is exerting a force of equal magnitude in the opposite direction on the other object. In other words, if I am pushing a boulder, Newton's third law says that the boulder is also pushing back with an equal amount of force in the opposite direction.

## Exceptions to Newton's Laws

These laws are good approximations for objects in everyday usage, and they consistently held up under experimental conditions for over 200 years. But like any other scientific law, the laws of motion only apply when given a certain set of constraints and cannot be assumed to be true when those predefined constraints are not met. In the case of Newton's laws, they have been shown to be wrong under some conditions.

One instance where they don't hold up is at very fast speeds, which in physics means speeds close to the speed of light. They also don't apply when very strong gravitational fields are involved, like the gravitational force from a black hole or a star. The laws also fail at very small scales, such as at the level of electrons.

While these limitations may seem impractical to consider, they actually have implications in some fields like engineering. For example, the network of satellites used by GPS devices has to account for these limitations. The GPS satellites are moving so fast that their clocks literally tick more slowly than clocks on the earth because of an effect known as time dilation. The effect is tiny, but it is enough that the entire GPS system would be virtually useless if not taken into account. Newton's laws of motion are not adequate for such a system.

Because of these limitations, Newton's laws have mostly been replaced by the work of Albert Einstein. In particular, Einstein's theory of special relativity does a much better job at describing motion, especially under the unusual conditions that limit Newton's laws. For example, the time dilation effect on GPS satellites is described by special relativity. Einstein's theories allow GPS satellites and other spacecraft to function properly, while Newton's laws do not work for those uses.

Nevertheless, because of their much greater simplicity compared to the theory of relativity, along with the fact that they are “good enough” under most cases, Newton's laws can still be used as close approximations to describe the movement of everyday objects. #science #physics #scientificlaws #isaacnewton

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