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# What Are Newton's Laws of Motion?

## Newton's First, Second and Third Laws of Motion

Isaac Newton (1642 - 1727)

Godfrey Kneller, 1688
Newton's Laws of Motion help us to understand how objects behave when they are standing still, when they are moving, and when forces act upon them. There are three laws of motion. Here is a description of Newton's Laws of Motion and a summary of what they mean.

### Newton's First Law of Motion

Newton's First Law of Motion states that an object in motion tends to stay in motion unless an external force acts upon it. Similarly, if the object is at rest, it will remain at rest unless an unbalanced force acts upon it. Newton's First Law of Motion is also known as the Law of Inertia.

Basically what Newton's First Law is saying is that objects behave predictably. If a ball is sitting on your table, it isn't going to start rolling or fall off the table unless a force acts upon it to cause it to do so. Moving objects don't change their direction unless a force causes them to move from their path.

### Newton's Second Law of Motion

Newton's Second Law of Motion states that when a force acts on an object, it will cause the object to accelerate. The larger the mass of the object, the greater the force will need to be to cause it to accelerate. This Law may be written as force = mass x acceleration or:

F = m * a

Another way to state the Second Law is to say it takes more force to move a heavy object than it does to move a light object. Simple, right?

### Newton's Third Law of Motion

Netwon's Third Law of Motion states that for every action, there is an equal and opposite reaction.

What this means is that pushing on an object causes that object to push back against you, the exact same amount, but in the opposite direction.

Anne Marie Helmenstine, Ph.D.