## Force: Newton's First and Second Laws

• Newton's Laws describe the action of objects in response to forces.
• (Digression) The response of an object to a given force is a measure of its inertial mass ... which turns out to be equivalent to its gravitational mass.
• Newton's Second Law states
```          Force = mass * acceleration
```
• This shows that the units of force must be
```                              kg * m
(kg) * (m/s^2) =   --------      (Newtons)
s^2
```
• Note that if the net force on a body is zero, then its acceleration must also be zero -- this is Newton's First Law.
• Here on earth, friction exerts a force on just about all objects, so they are always accelerating; that's what makes it hard to realize that the natural state of an object is to move with constant velocity (not be at rest).
• In order to figure out which way an object moves in response to several forces, and how fast it accelerates, it helps to break up all forces into X and Y components, the add up the components.

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A digression on how one can define mass...

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