1. Chapter 12
Section 1 Measuring Motion
Bellringer
Describe the location of a favorite place, using a reference point and reference directions. For example, “The library is at the corner of Madison Street and Monroe Street. It is two blocks west of the school and four blocks north of the bus stop.”
Write your response in your Science Journal.

2. Chapter 12
Section 1 Measuring Motion
What You Will Learn
Properties used to describe the motion of an object include a reference point, direction, speed, velocity, and acceleration.
Average speed can be calculated by dividing total distance by total time.
A change in velocity is due to a change in speed, direction, or both.
Speed and acceleration can be represented on graphs.

3. Motion and Reference Points
Chapter 12
Section 1 Measuring Motion
Motion and Reference Points
An object is in motion if it changes position over time in relation to a reference point.
A reference point is any object that appears to stay in place.
Features on Earth’s surface are often used as standard reference points.

4. Motion and Reference Points, continued
Chapter 12
Section 1 Measuring Motion
Motion and Reference Points, continued
Reference directions—such as north, south, east, west, up, or down—can be used to describe the direction of an object’s motion.
A grid can be used to describe motion in a two-dimensional system.

5. Chapter 12
Section 1 Measuring Motion
Average Speed
The speed of an object is the rate at which the object moves.
The speed of an object is rarely constant. So, it is useful to find the average speed of an object.

6. Average Speed, continued
Chapter 12
Section 1 Measuring Motion
Average Speed, continued
Average speed is the total distance traveled divided by the total time taken.
A graph of position versus time can show an object’s speed. On a graph of position versus time, the slope of the line is equal to the speed of the object.

7. Velocity: Direction Matters
Chapter 12
Section 1 Measuring Motion
Velocity: Direction Matters
Velocity is the speed of an object in a particular direction.
Velocity and speed do not have the same meaning.
Velocity must include a direction.

8. Velocity: Direction Matters, continued
Chapter 12
Section 1 Measuring Motion
Velocity: Direction Matters, continued
The velocity of an object is constant only if the speed and direction of the object do not change. So, constant velocity is always motion along a straight line.
The velocity of an object changes if the object’s speed, direction, or both change.

9. Chapter 12
Matter in Motion
Velocity

10. Chapter 12
Section 1 Measuring Motion
Acceleration
Acceleration is the rate at which velocity changes over time.
An object can accelerate by changing speed, direction, or both.
The units for acceleration are the units for velocity divided by a unit for time, usually meters per second per second, or (m/s)/s, which is also written as m/s2.

11. Chapter 12
Matter in Motion
Acceleration

12. Acceleration, continued
Chapter 12
Section 1 Measuring Motion
Acceleration, continued
Centripetal acceleration occurs when an object moves at a constant speed in circular motion.
A graph of speed versus time can show positive acceleration, no acceleration, and negative acceleration.

13. Chapter 12
Matter in Motion