1. Forces and motion How and How Fast

2. Motion and speed How can we calculate how fast an object is moving? How long will a journey take at a particular speed? Speed is a measure of how fast something is moving. The speed of an object tells us the distance it travels each second.

3. SPEED An Olympic sprinter will run about 10 meters every second. We say they are running at a speed of 10 meters per second. This can be written as 10 m/s.

4. Calculating speed To calculate speed: the distance travelled is divided by the time taken to travel that distance. During the journey the speed may change, meaning that the speed calculated is the average speed.

5. Calculating speed: Example average speed = distance travelled ÷ time taken A horse, takes 12 s to trot a distance of 96 m. Calculate the average speed of the horse during this part of its journey. information: distance travelled = 96 m time taken = 12 s.

6. Calculating speed: Example information: distance travelled = 96 m time taken = 12 s. calculation: average speed = distance travelled ÷ time taken =96m÷12s= 8m/s Answer:8m/s

7. Calculating Distance Travelled To calculate the distance travelled you need to know the time taken for the journey and the average speed during the journey. You then calculate the distance travelled using the following equation: distance travelled = average speed x time taken

8. Calculating Distance Travelled A sneeze travels at 160 km/hr

9. Calculating Distance Travelled Example A girl walks at an average speed of 2 m/s for 80 s. Calculate how far she walked in that time. information: average speed = 2 rn/s time taken = 80 s.

10. Calculating Distance Travelled calculation: distance travelled = average speed x time taken =2 m/s x 80 s =160 m.

11. Time Taken To calculate the time taken to travel a given distance when the average speed is known, use the following equation time taken = distance travelled ÷ average speed

12. Example Time Travelled A ferry transports cars across a river at an average speed of 4 m/s The river is 640 m wide Calculate the time that it takes for the ferry to cross the river. information: distance travelled = 640 m average speed = 4 m/s.

14. information: distance travelled = 640 m average speed = 4 m/s. calculation: time taken = distance travelled÷ average speed= 640 m ÷ 4 s =160 s.

15. Other units of speed It is not always a good idea to measure speeds in metres per second. A snail making its way along a garden path will be moving very slowly and it would be better to measure its speed in millimetres per second.

16. For a car travelling along a motorway at high speed it would be better to measure the speed in miles per hour or kilometres per hour The same equation is used to calculate the speed, but the appropritate units for distance and time must be used. To find the speed of the snail (mm/s) the distance should be measured in millimetres time in seconds.