1. Describing & Measuring Motion 9.1
A reference point is needed to decide if something is in motion
The SI units are used to describe distance
Centi - one-hundredth
Milli – one thousandth
Kilo – one thousand

2. Converting Units 22.5 m = 2,250 cm Practice Problem
- Describing and Measuring Motion
Converting Units
Practice Problem
How many centimeters are in 22.5 meters?
22.5 m = 2,250 cm

3. Speed and Velocity 9.2 SPEED = Distance
Time
The speed of most moving objects is not constant, therefore average speed is calculated
AVG SPEED = Total Distance
Total Time

4. Velocity Graphing Motion example = 25m/s southwest
requires speed and direction
Graphing Motion
SLOPE = Rise
Run
The steeper the slope the greater the speed

5. Acceleration= Final Speed – Initial Speed
Acceleration refers to ….
Changing Direction
Increasing Speed
Decreasing Speed
To determine the acceleration of an object moving in a straight line, you must calculate the change in speed per unit of time.
Acceleration= Final Speed – Initial Speed
Time

6. Calculating Acceleration
An example of Acceleration = 25m/s²

7. Calculating Acceleration
As a roller-coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its speed is 22 m/s. What is its average acceleration?
What information have you been given?
Initial speed = 4 m/s
Final Speed = 22 m/s
Time = 3 s

8. Calculating Acceleration
As a roller-coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its speed is 22 m/s. What is its average acceleration?
Acceleration = (Final speed – Initial speed)/Time
Acceleration = (22 m/s – 4 m/s)/3 s = 18 m/s/3 s
Acceleration = 6 m/s2
The roller-coaster car’s average acceleration is 6 m/s2.

9. Calculating Acceleration
Practice Problem
A falling raindrop accelerates from 10 m/s to 30 m/s in 2 seconds. What is the raindrop’s average acceleration?
(30 m/s – 10 m/s) ÷ 2 seconds = 10 m/s2

10. Calculating Acceleration
Practice Problem
A certain car can accelerate from rest to 27 m/s in 9 seconds. Find the car’s average acceleration.
(27 m/s – 0 m/s) ÷ 9 s = 27 m/s ÷ 9 s = 3 m/s2

11. Graphing Acceleration
You can use both a speed-versus-time graph and a distance-versus-time graph to analyze the motion of an accelerating object.