1. Acceleration

2. Acceleration is a vector quantity. When the speed of an object changes, it is accelerating. Acceleration demonstrates the change in speed per unit of time. Speed is measured in m/s, so acceleration is measured in (m/s)/s or m/s 2. Acceleration = POSITIVE Deceleration = NEGATIVE

3. Negative acceleration is sometimes called deceleration but this is not accurate...

4. Acceleration ( ) is the rate of change in the velocity of an object. acceleration = change in velocity time

5. An object undergoes constant or uniform acceleration if the change in velocity is the same throughout the time interval.

6. Average acceleration ( (moy) ) is the change in the velocity of an object (Δ ) during a time interval (t). Acceleration of an object at a given moment is called instantaneous acceleration.

7. Average acceleration Average acceleration is the relationship between the change in velocity and the time interval. a = For example, if a car moves from stopped to 5 m/s in 5 seconds, its average acceleration is: a = = 1m/s 2

8. Question 1 A hockey puck moves at a velocity of +8.2m/s on the ice. It is hit by a hockey stick during 0.25 s, which makes it follow the same trajectory in the same direction, going 21.3 m/s. Calculate the acceleration of the hockey puck.

9. Answer 1 a = (v f – v i ) ∆t a = (21.3m/s – 8.2m/s) = 52m/s 2 0.25s The puck accelerates at 52m/s 2.

10. Question 2 A car stopped at a stop sign presses on the gas and obtains a velocity of et +50.0 km/h in 9.2 s. What was the acceleration of the car in m/s 2 ?

11. Answer 2 a = (v f – v i ) ∆t 50km x 1000m x 1hr = 50 000m = 1 hr 1km 3600s 3600s 13.889 m/s a = (13.889 m/s – 0m/s) = 1.5 m/s 2 (significant digits) 9,2 s The car’s acceleration is 1.5 m/s 2.