FORCES
Newton's 3 Laws of Motion
1. An object will remain at rest or uniform velocity in a straight line unless acted upon by an external force.
2. Force is equal to the change in momentum per change in time. For a constant mass, force equals mass times acceleration.
3. For every action, there is an equal and opposite reaction.
Force
-
A force is a push or pull measured in Newtons (N)
-
Force is a vector quantity (has a certain direction)
-
Weight is the force of gravity. The direction of weight is down towards the center of the Earth.
-
The counter-force to weight is normal force (AKA reaction force). Both weight and normal force balance each other out.
-
Tension T can only be a pull and never a push.
-
Friction F tries to oppose the motion. It is parallel to the contact surface.
-
Normal R is perpendicular to the contact surface.
-
Friction and normal are mutually perpendicular F | R. They are surface contact forces.
-
Weight W is an action at a distance force.
Weight = mass x gravity
W = mg
SKETCHING AND INTERPRETING FREE-BODY DIAGRAMS
-
Tension T is sketched at whatever angle is given.
-
Friction F is sketched parallel to the contact surface.
-
Normal R is always sketched perpendicular to the contact surface.
-
Weight W is sketched from the center of an object
.png)
.png)
.png)