Chapter 4: Forces and Newton's Laws of Motion

4.1: The Concepts of Force and Mass

• ==Force==: a push or pull (vector)
• ==Contact force==: force that results from physical contact between two objects
• ==Non-contact force== (AKA action-at-a-distance forces): forces that are applied without physical contact
• ==Mass==: measure of matter/how much of something there is, measure of inertia (scalar)

4.2: Newton’s First Law of Motion

The first Law

• An object will continue to stay at rest or in motion unless an external net force acts upon it.
• ==Net force==: total sum of all forces acting on an object
  • A net force is not needed to sustain (a lack of) motion, only to change it.

Inertia and Mass

• ==Inertia==: natural tendency of an object to stay at rest or at a constant velocity
• ==Mass==: quantitative measure of inertia
• Greater inertia requires greater force to change an object’s state of motion.

An Inertial Reference Frame

• Inertial reference frame: a frame of comparison in which Newton’s first law is valid
• Different reference frames will produce different inertial results
  • Example: passenger in an accelerating car
  • Relative to the car: motion doesn’t change
  • Relative to the ground: motion changes

4.3: Newton’s Second Law of Motion