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Calculating Average Speed: Distance, Time, & Speed Formula

Learn how to calculate average speed using distance and time, with speed formula examples and unit conversions. Explore speed-time graphs and understand average vs. instantaneous speed.

alfredbennett
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Calculating Average Speed: Distance, Time, & Speed Formula

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  1. Distance, time and speed To work out the speedof an object you need to know: • the distance travelled • how long it took to travel that distance.

  2. Calculating average speed d total distance Averagespeed = s t total time formula triangle Average speed is calculated using this equation: Speed can be measured in different units, e.g. m/s, km/h, km/s, miles per hour. The units of distance and time will determine the units to be used for speed.

  3. Words and units

  4. Speed formula triangle

  5. Speed calculation example distance (in km) average speed (in km/h) = time (in h) 10km = = 0.5h A girl takes 30 minutes to travel around a cross-country ski course: a distance of 10km. Calculate her average speed in km/h. 10km 20km/h

  6. Speed calculation example – units distance (in m) average speed (in m/s) = time (in s) 10,000m = = 3600 s Sometimes the units have to be changed in a speed calculation. Calculate the average speed of the skier in m/s. 10km 2.8m/s

  7. Distance calculation A boy sets off for a walk around his village at an average speed of 3.6 km/h. How far will he travel in 30 minutes? Give your answer in km. distance (km) = speed (km/h) × time (h) = 3.6km/h ×0.5h = 1.8km

  8. Time calculation – question 1 distance time= speed 200m = 0.8m/s How long would it take the boy to walk 200m to the church, if his average speed was 0.8m/s? =250 seconds

  9. Car graphing activity – animation

  10. Distance–time graph

  11. distance distance time time Calculating speed from the gradient The slope of a graph is called the gradient. The gradient of the line in adistance–time graph equals the speed. Simple graphs use straight lines only, making it easy to calculate the gradient. It is difficult to calculate the gradient of ‘realistic’ graphs because the line is curved.

  12. B 70 60 50 40 distance (m) 30 20 A 10 0 0 1 2 3 4 5 6 7 8 9 time (s) What’s the speed? What is the speed of the object between points A and B? • the object has moved 60m (70 – 10) • it took 3s to move this distance (6 – 3) • speed = distance/time = 60/3 = 20m/s

  13. Speed–time graph

  14. B 70 60 50 40 distance (m) 30 20 A 10 0 0 1 2 3 4 5 6 7 8 9 time (s) What’s the speed? How can we work out the average speed of this object between points C and D? D • the object has moved 70m (70 – 0) • it took 9s to move this distance (9 – 0) • speed = distance/time C = 70/9 = 7.8m/s

  15. Average speed vs. instantaneous speed The speed of a race car at any point around a track is called the instantaneous speed. A car will have a different instantaneous speed at each of the points around the track. Average speed is the total distance travelled divided by the total time taken. It is never bigger than the instantaneous speed.

  16. Calculating average speeds

  17. Glossary

  18. Anagrams

  19. Multiple-choice quiz

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