Univeral law of gravitation:
The mathematical formula that relates the pull of gravity between two massive objects that are some distance apart.  F_g=Gm₁m₂/d²

Gravitation constant:
A proportionality constant that relates the strength of gravitational attraction in Newton’s law of universal gravitation. G=6.67x10^(-11) Nm²/kg²  This value always remains constant. 

Gravitational field: 
The map of influence that a massive body extends into space around itself. 

Rotational speed: 
Number of rotations or revolutions per unit of time, often measured in rpm, revolutions per minute.  Linear speed is the straight path distance moved per unit of time, also referred to as tangential speed.

Centripetal acceleration:
The acceleration that describes the change in direction for an object in a circular path.

Centripetal force:
A center seeking force for an object moving in a circular path.

Centrifugal force:
An apparent, but nonexistent, outward pointing force for an object moving in a circular path. A rotating object may seem to be pushed outward, but actually must be pulled inward in order to maintain any circular path.

Gravity is a force that you notice almost everyday.  This tutorial explains how to calculate or quantify that force.  The gravitational inverse square law depends upon the masses involved, and the distant between them.  A universal gravitational constant is also needed.

In previous tutorials, motion in a line was extensively described.  However, motion in a circle is also very common.  The rate at which an object moves in a circular path is described by rotational speed.  The rate at which its direction changes in that circular path is called centripetal acceleration.  The force that provides this acceleration is called centripetal force.  For motion in a circle, the dirction of motion is main quantity that will be described.

Specific Tutorial Features:

• Problem-solving techniques are used to work out and illustrate the example problems, step by step.
  
• Vector diagrams showing force components for a car traveling around a banked curve.

Series Features:

• Concept map showing inter-connections of new concepts in this tutorial and those previously introduced.
  
• Definition slides introduce terms as they are needed.
  
• Visual representation of concepts
  
• Animated examples—worked out step by step
  
• A concise summary is given at the conclusion of the tutorial.

Gravity

• Formula
  
• Gravitational constant
  
• Gravitational fields
  
• Gravitational pull at various points on Earth
  

Circular Motion

• Linear speed versus rotational speed
  
• Centripetal acceleration
  
• Centripetal force
  
• Centrifugal force
  
• Banked roads
  
• Simulated gravity