1. Acceleration (a vector quantity) is defined as the rate of change of velocity. It has units of m/s 2 Acceleration can be positive, negative, or zero. An object in uniform motion has no acceleration. An object with decreasing velocity has negative acceleration, assuming that the direction the object travels is considered positive. Since acceleration is a vector quantity, uniform motion means that both the magnitude and direction of the velocity are constant (acceleration is zero). Acceleration can be calculated using the equation: Accelerating Objects 13.1 VOCABULARY acceleration negative acceleration

2. Since the force of gravity is constant, the acceleration due to gravity is also constant. The acceleration of gravity near Earth’s surface is about 9.8 m/s 2 down. Accelerating Objects 13.1 VOCABULARY acceleration negative acceleration

3. An object with constant acceleration has a velocity–time graph that is a straight line. The slope of a velocity–time graph is acceleration. The area under the line represents displacement. When acceleration is not constant, the instantaneous acceleration is the slope of the tangent to the line of a velocity–time graph. A negative slope on a velocity–time graph indicates negative acceleration. Graphing Accelerated Motion 13.2 VOCABULARY instantaneous acceleration

4. There are three different types of motion graphs: position–time graphs velocity–time graphs acceleration–time graphs We can use each type of graph to analyze the motion of an object, or compare the motion of two different objects. Objects in Motion 13.4 VOCABULARY terminal velocity

5. Acceleration When an object changes speed or direction, it is changing its velocity. Acceleration is the rate of change of velocity. Falling objects are accelerated toward Earth by the force of gravity. When air resistance is negligible, the motion is known as free fall. 13 CHAPTER

6. Acceleration Velocity–time graphs can be used to determine information about an object’s motion. The slope of a velocity–time graph is acceleration. An object in uniform motion has no acceleration. Uniform motion means that both the magnitude of the velocity and the direction of the velocity must be constant. 13 CHAPTER

7. Acceleration Activity Consider the equation used to calculate acceleration: Complete the table below and provide examples of each type of acceleration. Read pages 373–376 in your textbook for information on positive, negative, and zero acceleration. 13 CHAPTER Real-world Examples Acceleration would equal zero if…1. 2. 3. Acceleration would be positive if…1. 2. 3. Acceleration would be negative if…1. 2. 3.

8. Acceleration 13 Key Ideas Acceleration is the rate of change of velocity. Falling objects are accelerated by the force of gravity. Velocity–time graphs can be used to determine information about an object’s motion. An object in uniform motion has no acceleration. CHAPTER