1. Ch 2. Motion in One Direction. What is the motion?
Object of interest – the object whose motion we are describing
Observer – the person or entity that is describing the motion of the object of interest

2. Unnumbered Figure Page 03
With respect to Tim, the ball is moving – its’ position is changing as time elapses.
With respect to Jan, the ball is not moving – it maintains constant position from the observer.

3. Motion is a change in an object’s position relative to a given observer during a certain interval of time.
Without identifying the observer, it is impossible to say whether an object of interest is moving.
Motion is relative.
The description of an object’s motion depends on the frame of reference from which it is being observed.
Unnumbered Figure Page 04

4. symbol for physical quantity
Position – the location of an object with respect to a particular coordinate system (usually indicated by x or y)
x = 2 m
units of measurement
symbol for physical quantity

5. Representations of Motion (so far)
Data table
Clock reading (time)
Position
t0 = 0.0 s
x0 = 1.00 m
t1 = 1.0 s
x1 = 2.42 m
t2 = 2.0 s
x2 = 4.13 m
t3 = 3.0 s
x3 = 5.52 m
t4 = 4.0 s
x4 = 7.26 m
t5 = 5.0 s
x5 = 8.41 m
t6 = 6.0 s
x6 = m
What additional representation could we create to make it easier to recognize trends in the data?
Motion diagram (spark tape)

6. Position-vs-Time Graph
The vertical axis represents the object’s position along the coordinate axis.
The horizontal axis represents the clock reading.

7. Why do we graph position instead of distance?
Knowing an object’s position over time tells you more about it’s motion because it distinguishes between forward motion and backward motion.

8. xi represents initial position; xf represents final position

9. We graph time on the horizontal axis (t axis).
Time is considered to be the independent variable, since time progresses even when there is no motion.
We graph time on the horizontal axis (t axis).
Position is the dependent variable (position changes with time).
We graph position on the vertical axis (x axis).

10. The vertical axis of the position-time graph represents the coordinate axis on which the object moved.

11. A trendline must take all data points into account,
Trendline – a smooth best-fit curve that passes as close as possible to the data points.
A trendline must take all data points into account,
and does not have to touch the first or last data points.

12. The slope of the position-vs-time graph
represents the object’s velocity.
The y-intercept of the position-vs-time graph
represents the object’s initial position (x0)

13. (t2, x2) = (6s, 10m)
(t1, x1) = (2s, 4m)