800m 2.29 m/s Speed-Time Graphs Pairs of cameras spot your number plate, start a timer, and then spot your number plate again leaving a traffic calming zone. 800m The speed cameras record that your car takes 350 seconds to move between them. Calculate the average speed of your car. 2.29 m/s

Speed-Time Graphs WHAT – We are learning how to identify shapes of speed-time graphs and how to use them in calculating quantities. WHY – So that we can appreciate the differences between motion graphs of similar appearances. HOW – Watching a video clip to collect data and sketch a speed-time graph. Using speed-time graphs to help us calculate distances travelled.

Chose a car: http://www.youtube.com/watch?v=Guehl-PcMB4 Take notice of how fast your car travels throughout the part of the race you watch.

We can show the speed (or velocity) of an object by drawing a Velocity-Time Graph. It is very similar to a Distance-Time Graph but instead of plotting the distance you are away from something, you plot the speed you are travelling at.

Speed-Time graphs What does this tell us about an object‘s motion? (m/s) Time (s) The object’s speed is getting faster and faster every second. When speed is increasing we say it is accelerating. We measure acceleration in m/s2. The steeper the gradient, the bigger the acceleration. As the line is straight, it is a constant acceleration.

Speed-Time graphs What does this tell us about an object‘s motion? (m/s) Time (s) The object’s speed is not changing as time progresses. A horizontal line above 0m/s is a constant speed.

Speed-Time graphs What does this tell us about an object‘s motion? (m/s) Time (s) This horizontal line is at 0m/s speed. The object is not moving. It is stationary.

Speed-Time graphs What does this tell us about an object‘s motion? (m/s) Time (s) The object’s speed is getting slower and slower every second. When speed is decreasing we say it is decelerating. We measure deceleration in m/s2 just like acceleration. The steeper the gradient, the bigger the deceleration. As the line is straight, it is a constant deceleration.

Speed-Time graphs What does this tell us about an object‘s motion? E (m/s) C D F B A Time (s) Between A-B : Stationary Between B-C : Large constant acceleration Between C-D : Constant speed Between D-E : Small constant acceleration [compared to between B-C] Between E-F : Large constant deceleration

What else can we get from a speed-time graph? Speed-Time graphs What else can we get from a speed-time graph? Distance Travelled ! Speed (m/s) Height Base Time (s) We can calculate how far an object has travelled by working out the area under the graph. Distance is measured in metres (m). In the above example, the area under the graph is a triangle. Area = ½ x Base x Height

How would you find the distance travelled in this case? Speed-Time graphs How would you find the distance travelled in this case? Speed (m/s) width length Time (s) The object is moving with a constant speed. The area under this graph would be a rectangle. Area = length x width

Draw a Velocity-time Graph for your day. Mine looks something like this: 5km/h 0km/h 8am 12pm 4pm 8pm

Draw a Velocity-Time Graph for the race of your car. Chose a car: http://www.youtube.com/watch?v=Guehl-PcMB4 Draw a Velocity-Time Graph for the race of your car.