Interpreting Motion

How to read a position vs. time graph.

Position vs. Time Graphs

Stationary Constant positive velocity

Constant negative velocity

Position vs.Time graphs

Changing velocity

(increasing)

Changing velocity (decreasing)

If you want to know what the average velocity is calculate the slope.

Slope = Δd / Δt =Vavg

Δd = df - di

Δt = tf - ti

Using slope to predict motion

On a position vs. time graphIf slope is 0, then velocity is 0.If slope is positive, velocity is

constant in positive direction.If slope is negative, velocity is

constant in the opposite direction.If slope is changing, velocity is

changing. (i.e. you are accelerating)

d(m)

t(s)

A

Object A is stationary at some positive position from the origin.

d(m)

t(s)

B

Object B moves away from origin with a constant positive velocity.

d(m)

t(s)

C

Object C starts at a positive position and moves away from the origin with a constant positive velocity.

d(m)

t(s)

D

Object D moves away from the origin at a constant positive velocity.

d(m)

t(s)

A

B

D

C

Slower than B or C.

Same velocity as B.

East

High St.

West

EA

B

D

C

On your own…

pg 85 #2-3 and pg87 #5 and 8

Finding the Equation

0 1 2 3 4 5 60

2

4

6

8

10

12

14

time (s)

po

sit

ion

(m

)

y = mx +bd = 2t+2y =

x =

m = ∆y/∆x (6m- 4m)/ (2s-1s)= 2m/s

Finding position

Vavg = Δd / Δt

Vavg = (df –di)/Δt

df = di + Vavg Δt

y = b + mx

On your own…

pg 89 #9-12