Moving Things – Introduction to Motion

Motion: An object is in motion if its position changes with respect to a reference point with time.

Rest: An object is at rest if its position does not change with respect to a reference point with time.

Key Points:

Motion and rest are relative concepts
Same object can be in motion and at rest simultaneously depending on reference point
Time is essential factor in determining motion

Classic Example – Bus Journey:

Passengers relative to bus: At rest (positions don’t change relative to bus)
Passengers relative to roadside objects: In motion (positions change relative to trees, buildings)
Bus relative to road: In motion
Bus relative to another bus traveling at same speed in same direction: At rest

Practical Applications:

Airplane passengers: At rest relative to plane, in motion relative to ground
Train travel: At rest relative to train, in motion relative to stations
Earth’s rotation: At rest relative to Earth, in motion relative to Sun