1. Speed, Velocity, Acceleration Chapter 39

2. Speed The speed of an object is the distance it travels in unit time(units : m/s). Speed = Distance Time

3. Different speeds Below are some examples of different speeds:  Speed of a common snail = 0.0036 km/h (0.0023 mph)snail  A brisk walk = 6km/h (3.75 mph) Olympic sprinters = 36km/h (22.5 mph) (average speed over 100 metres) Olympic  Speed limit on a French autoroute = 130km/h (80 mph)Frenchautoroute  Top cruising speed of a Boeing 747-400 = 913km/h (567 mph)Boeing 747-400  Official air speed record = 3,529 km/h (2,188 mph)air speed record  Space shuttle on re-entry = 28,000km/h (17,500 mph Space shuttle

5. Velocity Velocity is speed in a given direction. i.e. 10m/s due south.

6. Acceleration. Acceleration is the change in velocity per second.(Units m/s 2 ) Acceleration = Final velocity – Initial velocity Time taken = 27m/s - 9m/s 6s = 3m/s/s. The velocity of a car changes from 9m/s to 27m/s in 6 s.What is its acceleration? Answer:

7. Draw a graph of the following table i.Which walker is going faster? ii.How long does it take for walker B to travel 11 m? iii.How far apart are the walkers after 2.5 sec? iv.Is the speed of walker A constant? v.What is the speed of each walker?

8. Answers. (i)Walker A (ii)5.5 sec (iii)2.5 m (iv) The graph for walker A is a straight line. Therefore A’s speed is a constant. (v)Walker A Speed = Distance 21 = 3 m/s Time 7 Walker B Speed = Distance12 = 2m/s Time 6

9. Distance time Graph