Forces
by Danny Choi
1. 3rd law
1.1. for every force, there is a reaction force
1.2. if force is A on B, reaction force is B on A
1.3. action and reaction forces will NEVER act on the same object
1.4. same magnitude and opposite direction
2. inertia
2.1. a measure of how difficult for an obj to change its state of motion
2.1.1. e.g change direction of motion
2.1.2. e.g. start moving from rest
2.1.3. e.g. come to a stop from moving
2.2. affected by MASS only
3. types of forces
3.1. NCF
3.1.1. must show 90 degree angle
3.2. Tension
3.2.1. T along the same cable is the same
3.2.2. always draw along the cable
3.2.3. always act away from obj
3.3. weight
3.3.1. W = mg
3.4. friction
3.4.1. NOT affected by surface area
3.4.2. affected by forces pressing the obj and surface together
3.4.3. affected by surface roughness
3.5. air resistance
3.5.1. affected by speed of obj
3.5.2. affected by shape of obj
3.5.3. affected by density of the medium
4. vector diagram
5. 1st law
5.1. in the absence of net-force
5.1.1. remain stationary if it was stationary
5.1.2. move at constant v if already moving
6. 2nd law
6.1. F-net is the sum of forces
6.1.1. direction of F-net and a are the same
6.2. F-net = ma
6.3. if constant v, means F-net = 0
6.4. if F-net = 0, only means a = 0
6.4.1. if obj was stationary, obj remain stationary
6.4.2. if obj was moving, obj move at constant v