Forces and Motion (chpt. 12) Definitions
Force: A push or a pull that acts on an object. A force can cause a resting object to
move, or it can accelerate a moving object by changing the object’s speed or
direction. Units are Newtons (N). A Newton is equal to
𝑘𝑔∙𝑚
𝑠2
.
Friction: Force that opposes the motion of objects that touch as they move past each
other. (Resultant force of objects rubbing against each other.)
Static Friction: Friction force that acts on objects that are not moving.
Sliding Friction: Force that opposes the direction of motion of an object as it slides over
a surface.
Rolling Friction: Friction force that acts on rolling objects.
Fluid Friction: Force that opposes the motion of an object through a fluid.
Gravity: Force that acts between any two masses, pulling them together. Earth’s
gravity acts downward toward the center of Earth.
Newton’s 1st Law of Motion: Objects in motion stay in motion and objects at rest stay at
rest unless a force acts on the object.
Inertia: Tendency of an object to resist a change in motion.
Newton’s 2nd Law of Motion: F = m * a
Force equals mass times acceleration.
Newton’s 3rd Law of Motion: Whenever one object exerts a force on a second object,
the second object exerts an equal and opposite force back. Action/Reaction
pairs of force.
Momentum: M = m * v Momentum is mass times velocity. Units of momentum are
𝑘𝑔∙𝑚
𝑠
Universal Forces: Universal forces include electromagnetic forces, nuclear forces, and
gravitational force.