1. Forces and the Laws of Motion
Newton’s Second and Third Laws

2. Newton’s Second Law Force is proportional mass and acceleration
More massive objects require more force to accelerate
Newton’s Second Law – The acceleration of an object is directly proportional to the net external force acting on the object and inversely proportional to the object’s mass

3. Newton’s Second Law Net external force = mass x acceleration
ΣF =ma
ΣF is the vector sum of all of the forces acting on an object
m is the mass of the object
a is the acceleration of the object
Often easier to break force and acceleration down into x and y components and then use Pythagorean theorem and inverse tangent to find net force and direction

4. Newton’s Third Law
Forces, including field forces, always exist in pairs
When you apply force to an object, the object returns that force to you
Newton’s Third Law – If two objects interact, the magnitude of the force exerted on object 1 by object 2 is equal to the magnitude of the force simultaneously exerted on object 2 by object 1, and those two forces are opposite in direction

5. Newton’s Third Law
For every action force there is an equal and opposite reaction force
Action-reaction pair – a pair of simultaneous equal but opposite forces resulting from the interaction of two objects
Action and reaction forces act on different objects, but involve the same two objects

6. Newton’s Third Law