Frame of Reference, Position and Displacement
A frame of reference is the coordinate system and clock from which motion is measured; displacement is the vector from initial to final position.
What is Frame of Reference, Position and Displacement?
A frame of reference is the coordinate system and clock from which motion is measured; displacement is the vector from initial to final position.
Key formula / rule: Displacement is a vector; distance is a scalar path length.
Key points
- Define frame of reference, position, distance and displacement for a body in one dimension.
- Compute distance and displacement for a to-and-fro journey.
Common exam trap
Treating distance and displacement as interchangeable in to-and-fro motion.
Definitions
- Term
Frame of Reference, Position and Displacement
- Meaning
A frame of reference is the coordinate system and clock from which motion is measured; displacement is the vector from initial to final position.
- Term
Frame of Reference, Position and Displacement — explanation
- Meaning
Motion has no meaning without a frame. Once an origin and axis are fixed, position x(t) is a signed number and displacement is the change in that number. Distance travelled adds path length regardless of sign, so it is never smaller than the magnitude of displacement.
Learning objectives
Define frame of reference, position, distance and displacement for a body in one dimension.
Compute distance and displacement for a to-and-fro journey.
Formulae
- Key point
Displacement is a vector; distance is a scalar path length.
- Key point
|Displacement| ≤ distance, equality only for unidirectional motion.
- Key point
A different frame changes position values but not the displacement between two events in the same frame.
Common mistakes
Treating distance and displacement as interchangeable in to-and-fro motion.
Forgetting the sign of displacement when the body reverses direction.
Keywords
Frame
Reference
Position
Displacement
Practice preview
What is the primary purpose of a frame of reference in physics?…
easy
Which of the following statements correctly describes displacement?…
easy
Which of the following statements about displacement is INCORRECT?…
medium