Speed, Velocity, and Acceleration

1. Speed, Velocity, and Acceleration “I Feel the Need, the Need for Speed!”

2. Speed • Speed, velocity, and acceleration describe how an object’s position and motion change through time. • Rates measure change in something over a length of time. • Speed is the rate of change of distance over time.

3. Constant Speed • An object moving at constant speed travels the same distance each second. • This hurdler is moving at a constant speed of 5m/second.

4. Changing Speed • A car driving in town must slow down and speed up, therefore its speed is not constant. • The car’s speed at any given time is called its instantaneous speed. • An object moving at a constant speed has the same instantaneous speed at all times.

5. Average Speed • Average speed is the total distance traveled divided by the total time. If you know any 2 of the variables, you can calculate the missing variable. What is the relationship between distance, average speed, and time?

6. Velocity • Velocity is the speed and direction of a moving object. • Speed is the rate of change of distance with time. • Velocity is a vector because it has both direction and size. • The size of a velocity vector is the speed.

7. Acceleration • Acceleration is the rate at which velocity changes with time. (Which of these graphs shows positive acceleration? Which shows negative acceleration?) Acceleration

8. Acceleration (cont’d) • The horses on the carousel are moving at a constant speed, but changing direction, so they are constantly changing velocity and, therefore, accelerating.

9. Lesson 1-2: Review Acceleration is the rate of change of ____. A velocity B speed C time D direction

10. Lesson 1-2: Review A car stopping at a red light is and example of a(n) ____. A displacement B acceleration C direction D velocity

11. Lesson 1-2: Review It takes a runner 42.1 s to run a distance of 150 m. What is the runner’s average speed? A 0.28 m/s B 3.56 m/s C1.75 m/s D6.31 m/s