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Learn about acceleration, its calculation methods, effects on speed, and direction changes, illustrated with examples. Discover how to analyze acceleration from graphs and answer related questions effectively.
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Acceleration Chapter 9.3 Page 350
Objectives of 9.3 • Know how to describe a change in velocity in terms of speed or direction or both. • Know how to answer questions about a change in position over time from a graph. • Know how to answer questions about a change in speed over time from a graph.
Acceleration • Acceleration: the rate at which velocity changes. • Therefore acceleration can mean an increase in speed, a decrease in speed (negative acceleration) or a change in direction! • The moon continually accelerates because it is constantly changing direction.
Acceleration • Acceleration can be calculated! • To calculate acceleration, you need to know the final speed, initial speed and the time. • Acceleration tells how the speed changes during a specific time period. It is the rate at which the speed of an object changes.
How to Calculate Acceleration • Since acceleration describes the rate at which velocity changes, you must be able to calculate the change in velocity over time. Acceleration= Final Velocity – Initial Velocity Time Negative Number: Negative Acceleration • Slowing Down Positive Number: Positive Acceleration • Speeding Up Zero: No Acceleration • You are not experiencing a change in velocity • No change in speed, No change in direction
Example Acceleration Problem • A roller coaster car rapidly picks up speed as it rolls down a slope. As it starts down the slope, its speed is 4 m/s. But 3 seconds later, at the bottom of the slope, its speed is 22 m/s. What is its average acceleration? Initial Velocity: 4 m/s Final Velocity: 22 m/s Time: 3 s A. Acceleration= 22 m/s – 4 m/s 3 s B. Acceleration= 18 m/sC. Accel.= 6 m/s2 3 s
Questions • According to the scientific meaning, which of these sentences are true? Why? • When you step on the gas, the car accelerates. • When you step on the brake, the car accelerates. • What are three ways a car can accelerate? • What kind of motion does acceleration refer to? • How do you calculate acceleration? • What number should you use for the initial speed if an object starts out at rest?
Graphing Acceleration • You can use both a speed-versus-time graph to analyze the motion of an accelerating object.
Graphing Acceleration • You can use a distance-versus-time graph to analyze the motion of an accelerating object.