1. Table of Contents M – Ch 1 – Section 1 M – Ch 1 – Section 3
Describing and Measuring Motion
Acceleration
M – Ch 1 – Section 1
M – Ch 1 – Section 3

2. Book M – Ch 1 – Section 1 (Page 6-15)
Describing Motion
An object is in motion if its distance from another object is changing.
A reference point is a place or object used for comparison to determine if something is in motion.
An object is in motion if it changes position relative to a reference point.
Examples of reference points – trees, signs, or buildings (stationary objects).

3. - Describing and Measuring Motion
Relative Motion - Whether or not an object is in motion depends on the reference point you choose.

4. Book M – Ch 1 – Section 1 (Page 6-15) Measuring Distance
- Describing and Measuring Motion
Book M – Ch 1 – Section 1 (Page 6-15) Measuring Distance
You can use units of measurement to describe motion precisely.
The International System of Units (SI) is used by scientists all over the world so they can communicate clearly about measurements.
The SI unit of length is meter.
There are also other SI units to describe quantities other than length.

5. Converting Units - Describing and Measuring Motion
Use a conversion factor to convert one metric unit to another. A conversion factor is a fraction in which the numerator and denominator represent equal amounts in different units. Multiply the number you want to convert by the conversion factor.
Suppose you want to know how many millimeters (mm) are in 14.5 meters (m). Since there are 1,000 millimeters in 1 meter, the conversion factor is:
1,000 mm/1 m
Multiply 14.5 meters by the conversion factor to find millimeters.
14.5 m X 1,000 mm/1 m
= 14.5 X 1,000 mm
= 14,500 mm

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

8. Book M – Ch 1 – Section 1 (Page 6-15) Calculating Speed
If you know the distance an object travels in a certain amount of time, you can calculate the speed of an object.
The speed of an object is the distance the object travels per unit of time.
To calculate average speed, divide the total distance by the total time.
Instantaneous speed is the rate at which an object is moving at a given instant in time.

9. Book M – Ch 1 – Section 1 (Page 6-15) Calculating Speed
- Describing and Measuring Motion
Book M – Ch 1 – Section 1 (Page 6-15) Calculating Speed
If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object.

10. - Describing and Measuring Motion
Calculating Speed
Practice Problem
Christopher rode his bicycle 60 kilometers in 4 hours. How fast was he going?
Speed = 15 km/hr

11. Book M – Ch 1 – Section 1 (Page 6-15) Velocity
When you know both the speed and direction of an object’s motion, you know the velocity of the object.
Speed in a given direction is called velocity.

12. Book M – Ch 1 – Section 1 (Page 6-15) Graphing Motion
- Describing and Measuring Motion
Book M – Ch 1 – Section 1 (Page 6-15) Graphing Motion
You can show the motion of an object on a line graph in which you plot distance versus time.

13. Book M – Ch 1 – Section 3 (Page 22-27)
Acceleration
Scientists define acceleration as the rate at which velocity changes.
In science, acceleration refers to increasing speed, decreasing speed, or changing direction.
Increasing speed – acceleration
Decreasing speed – deceleration or negative acceleration

14. Book M – Ch 1 – Section 3 (Page 22-27) Calculating Acceleration
To determine the acceleration of an object moving in a straight line, you must calculate the change in speed per unit of time.

15. 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?
Read and Understand
What information have you been given?
Initial speed = 4 m/s
Final Speed = 22 m/s
Time = 3 s

16. 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?
Plan and Solve
What quantity are you trying to calculate?
The average acceleration of the roller-coaster car
What formula contains the given quantities and the unknown quantity?
Acceleration = (Final speed – Initial speed)/Time
Perform the calculation.
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.

17. 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?
Look Back and Check
Does your answer make sense?
The answer is reasonable. If the car’s speed increases by 6 m/s each second, its speed will be 10 m/s after 1 second, 16 m/s after 2 seconds, and 22 m/s after 3 seconds.

18. 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

19. 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

20. Book M – Ch 1 – Section 3 (Page 22-27) 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.

21. Click the SciLinks button for links on acceleration.