1. September 3, 2010 Average Speed, Velocity, Acceleration

2. Average Speed and Average Velocity • Average speed describes how fast a particle is moving. It is calculated by: • Average velocity describes how fast the displacement is changing with respect to time: always positive sign gives direction

3. Average Acceleration • Average acceleration describes how fast the velocity is changing with respect to time. The equation is: sign determines direction

4. Sample problem: A motorist drives north at 20 m/s for 20 km and then continues north at 30 m/s for another 20 km. What is his average velocity? 24 m/s

5. Sample problem: It takes the motorist one minute to change his speed from 20 m/s to 30 m/s. What is his average acceleration? 0.167 m/s2

6. B A Dx Dt Average Velocity from a Graph x t

7. A x B Dx Dt t Average Velocity from a Graph

8. B A Dx Dt Average Acceleration from a Graph v t

9. x(m) 3 2 1 0 A -1 B -2 -3 0 0.1 0.2 0.3 0.4 0.5 t(s) • Sample problem: From the graph, determine the average velocity for the particle as it moves from point A to point B. -1.0 m/s

10. x(m) 3 2 1 0 A -1 B -2 -3 0 0.1 0.2 0.3 0.4 0.5 t(s) • Sample problem: From the graph, determine the average speed for the particle as it moves from point A to point B. 1.0 m/s