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