Centripetal Force
A Force Directed Toward The Center Of A Circular Path, Required For Circular Motion.

Fictitious Force
An Apparent Force Experienced In A Noninertial Frame, Such As Centrifugal Force.

Noninertial Frame
A Frame Of Reference That Is Accelerating, Requiring The Use Of Fictitious Forces To Describe Motion.

Inertial Frame
A Frame Of Reference In Which Objects Not Subject To Forces Move At Constant Velocity.

Length Contraction
A Phenomenon In Special Relativity In Which Moving Objects Appear Shortened Along The Direction Of Motion.

Time Dilation
A Phenomenon In Special Relativity In Which Time Passes More Slowly For Objects Moving At High Speeds.

Spacetime
A Four Dimensional Continuum Combining Space And Time, Central To Relativity.

General Relativity
A Theory Describing Gravity As The Curvature Of Spacetime Caused By Mass And Energy.

Special Relativity
A Theory Describing The Relationship Between Space And Time At High Speeds, Including Time Dilation And Length Contraction.

Relativity
A Branch Of Physics Developed By Einstein That Includes Special And General Relativity.