1. Newton’s Second Law
“ Forces do not cause motion. Forces cause accelerations”

2. Newton’s 2nd Law
Recall
acceleration is the rate of change of velocity – either speed or direction
Fnet is the sum of all the forces acting on an object – it is not the name of any one particular force.
Therefore, you can’t apply a net force to an object, you can only apply a force that may result in a net force.
If the sum is not = 0, then we say there is a net force acting on an object.
Newton’s 2nd Law: a net force causes a mass to accelerate
to change its state of motion
to do something different than it’s already doing
A constant (consistent amount of) net force causes a constant acceleration
Any size net force, no matter how small, causes any size mass, no matter how big, to accelerate.

3. The Math of Newton’s 2nd Law…
a α Fnet (direct) so, for the same mass,
as Fnet changes, the a changes by the same multiple
Ex: If Fnet = 3 N causes a = 8 m/s2,
then if Fnet = 9 N on the same m, the a = _____
a α 1/m (inverse) so, for the same Fnet,
as m changes, the a changes by the inverse multiple
Ex: If m = 10 kg has an a = 4 m/s2,
then if m = 5 kg with same Fnet, the a = _____
But we can combine these 2 proportions to get
a α Fnet / m
where the constant to make the proportion an equation has a value of 1, so
a = (1) Fnet / m
or just a = Fnet / m
or more commonly, Fnet = ma

4. The Units of the Fnet = ma equation:
1 Newton = 1 kg * 1 m/s2
so then if a = Fnet / m
the units are: = N / kg
= kg*m/s2 kg
= m/s2 , which makes sense for a
or if m = Fnet / a
the units are: = N / m/s2
= kg* m/s2
m/s2
= kg , which makes sense for m
All of this applies to W = mg too! See it ?!?!?
Fnet = ma is a more generic form, good for any force, whereas W = mg is only appropriate to determine the force of weight using the acceleration due to gravity.