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Forces and motion

Forces and motion. How and How Fast. 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. SPEED.

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Forces and motion

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  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.

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

  14. Other units of speed • It isnot 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.

  15. 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.

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