= Chapter 4

== Motion and Forces

/ Newton's first law: An object willre main at rest or continue moving in a straight line at the same speed unless it has forces acting on it
/ Contact forces: Forces that act on an object by touching it
/ Long-range forces: Forces that act on an object without physical contact

Examples of forces:

- Weight ($arrow(w)$)
- Tension ($arrow(T)$)

== Newton's Second Law

$arrow(F)_"net" = m arrow(a)$

== Newton's Third Law

/ Interaction: Mutual influence of two objects on each other

An action/reaction pair of forces exists as a pair or not at all

/ Newton's Third Law: Every force occurs as one member of an action/reaction pair of forces

- The two members of an action/reaction pair of forces act on different objects
- The two members of an action/reaction pair point in *opposite directions* but have the *same magnitude*
