1. Table of Contents Describing and Measuring Motion
Slow Motion on Planet Earth
Acceleration

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

3. Measuring Distance - Describing and Measuring Motion
You can measure distances shorter than 1 meter in centimeters. The wingspan of the butterfly is 7 cm.

4. 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 15.5 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

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

6. Calculating Speed - Describing and Measuring Motion
If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object.

7. Graphing Motion - Describing and Measuring Motion
You can show the motion of an object on a line graph in which you plot distance versus time.

8. Graphing Motion Activity
- Describing and Measuring Motion
Graphing Motion Activity
Click the Active Art button to open a browser window and access Active Art about graphing motion.

9. Using Prior Knowledge - Describing and Measuring Motion
Before you read, write what you know about motion in a graphic organizer like the one below. As you read, write what you learn.
What You Know
A moving object changes position.
Objects move at different speeds.
What You Learned
Motion is compared to a reference point.
The SI unit of length is the meter.

10. Click the Video button to watch a movie about velocity.
- Describing and Measuring Motion
Velocity
Click the Video button to watch a movie about velocity.

11. Data Sharing Lab - Describing and Measuring Motion
Click the PHSchool.com button for an activity about sharing data for the Skills Lab Inclined to Roll.

12. End of Section: Describing and Measuring Motion

13. Earth’s Plates - Slow Motion on Planet Earth
According to the theory of plate tectonics, Earth’s landmasses have changed position over time
because they are part of plates that are slowly moving.

14. Plate Movement - Slow Motion on Planet Earth
Some plates move at a rate of several centimeters each year. Others move only a few millimeters per year.

15. Continental Drift Activity
- Slow Motion on Planet Earth
Continental Drift Activity
Click the Active Art button to open a browser window and access Active Art about continental drift.

16. Previewing Visuals - Slow Motion on Planet Earth
Before you read, preview Figure 8. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions.
Previewing Figure 8
Q. How have the positions of the continents changed over time?
A. The distance between the continents has increased.
Q. What causes Earth’s plates to move?
A. Slow-moving currents beneath Earth’s outer layer cause the plates to move.

17. End of Section: Slow Motion on Planet Earth

18. 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.

19. 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

20. 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.

21. 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.

22. 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

23. Calculating Acceleration
Practice Problem
A certain car can accelerate from rest to 2.7 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

24. 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.

25. Identifying Main Ideas
- Acceleration
Identifying Main Ideas
As you read the section “What is Acceleration?”, write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea.
Main Idea
In science, acceleration refers to...
Detail
Detail
Detail
Increasing speed
Decreasing speed
Changing direction

26. Click the SciLinks button for links on acceleration.

27. End of Section: Acceleration

28. Graphic Organizer Motion Reference point Distance ÷ Time Speed
is described relative to a
is measured by
Reference point
Distance ÷ Time
in a given direction is called
equals
Speed
Velocity

29. End of Section: Graphic Organizer