Reference Frame and Position

Position Always Asks From Where

If you say, "I am $30 \text{ m}$ from the store," your friend can still ask, "which direction?" If you say, "I am east," your friend can still ask, "how far?"

In physics, position is the location of an object measured from a chosen reference point. That chosen point is called a reference frame. A reference frame can be a store, a house, a flagpole, the start line of a race, or the zero point on a coordinate axis.

A complete position statement names the reference point, value, unit, and direction.

If motion happens along one straight line, we can choose one direction as positive. In the street example, east is positive and west is negative.

x_{\text{relative}}=x_{\text{object}}-x_{\text{reference}}

Position Always Asks From Where

If you say, "I am

30 \text{ m}

from the store," your friend can still ask, "which direction?" If you say, "I am east," your friend can still ask, "how far?"

A complete position statement names the reference point, value, unit, and direction.

If motion happens along one straight line, we can choose one direction as positive. In the street example, east is positive and west is negative.

x_{\text{relative}}=x_{\text{object}}-x_{\text{reference}}

Reference frame	Object position on the street line	Object relative position
Store at $0 \text{ m}$	Object at $30 \text{ m}$	$+30 \text{ m}$ east
Rani's house at $20 \text{ m}$	Object at $30 \text{ m}$	$+10 \text{ m}$ east
Naya's house at $50 \text{ m}$	Object at $30 \text{ m}$	$-20 \text{ m}$ or $20 \text{ m}$ west

Reference Frame and Position

Position Always Asks From Where

Reference Frame and Position

Position Always Asks From Where

Position from Different References

Reading Sign and Direction

A Position Sentence That Stays Clear

A Position Sentence from the Store