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

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.

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

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.