Ch. 4: Understanding Motion, Energy, & Gravity

Speed

Rate at which an object moves.

Velocity

Speed and direction

Momentum

Mass X Velocity

Net Force

Changes momentum, which generally means an acceleration (change in velocity).

Angular Momentum

Describes objects that are spinning or moving in circles.

Torque

Needed to change an object’s angular momentum.

Mass

A measure of the amount of matter in an object.

Weight

The force that a scale (or gravity) exerts upon an object.

Newton’s First Law

An object moves at constant velocity unless a net force acts to change its speed or direction.

Newton’s Second Law

Net force = Mass X Acceleration (Constant Mass)

Newton’s Third Law

For every force, there is always an equal and opposite reaction force.

Conservation of Momentum

The total momentum of interacting objects cannot change unless an external force is acting on them.

Conservation of Angular Momentum

The angular momentum of an object cannot change unless a torque is acting on it.

Kinetic Energy

Energy in motion

Radiative Energy

Light energy

Potential Energy

Stored energy

Gravitational Potential Energy

Depends on an object’s mass, the strength of gravity, and its height above the ground

Mass Energy

Mass itself is a form of energy, E=mc squared

Thermal Energy

The collective kinetic energy of many particles.

Temperature

A measure of the average kinetic energy of the many particles in a substance.

Bound Orbit

Orbital paths in the form of ellipses.

Unbound Orbit

Orbital paths that are not ellipses, parabolas and hyperbolas.

Center of Mass

Because of angular momentum conservation, orbiting objects orbit around their center of mass.

Escape Velocity

If an object gains enough orbital energy, it may escape (change from a bound to an unbound orbit).

Tidal Force

Moon’s gravity pulls harder on near side of Earth. Size of tides depends on phase of moon.