# The Net Force

##     BHS -> Staff -> Mr. Stanbrough -> Physics -> Mechanics -> Newton's Laws -> Newton's First Law -> this page

## Why is "Net Force" Important?

"Net force" is a central idea of dynamics. Here's why:

Newton's Laws are the big deal in dynamics. Newton's First Law can be stated:

If the net force on an object is zero, its acceleration will be zero.

You will soon find out that Newton's Second Law says: where Fnet means "net force".

In order to use Newton's Laws, the first thing you need to know is "What is the net force".

## Finding the Net Force:

In Physics 1, you will need to be able to calculate the net force on an object in the five situations shown below. If no forces act on an object, the net force on the object is zero. Although this happens in physics problems, it is very unlikely in practice that an object will have no forces at all acting on it. If there is just one force on an object, then that force is the net force. In the diagram at left, the net force is 5 Newtons to the right. For example in free fall, the net force on an object equals its weight - the one force pulling on it. If 2 forces push or pull on an object in opposite directions, and the two forces cancel each other exactly, the net force is zero. If two forces act on an object in opposite directions and they don't exactly cancel, what is left over is the net force (the difference in the forces). In the diagram at left, the net force is 2 Newtons to the right. If two(or more) forces act on an object in the same direction, the net force is the sum of the forces. In the diagram at left, the net force is 10 Newtons to the right.

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