Speed and Acceleration

1. Cars Speed and Acceleration

2. Speed Criteria A C E Starter – Describe how your car over comes/uses the forces acting upon it… Use your research to help you

3. Put the following in order …1. of speed2. in some creative way you choose

4. 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.

5. Calculating Average Speed total distance d average speed = total time s × t 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 used will determine the units to be used for speed.

6. Speed formula triangle

7. Speed calculation example d (distance in km) average speed (in km/h) = t (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

8. Speed calculation example – units d (distance inm) average speed (in m/s) = t (time in s) 10,000m = 1,800 s Sometimes the units have to be changed in a speed calculation. Calculate the average speed of the skier in m/s. 10km = 5.6m/s 30 × 60

9. 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) x time (h) = 3.6 km/h x 0.5 h = 1.8 km

10. Time calculation – Question 1 distance time= speed 200m = 1.6m/s How long would it take the boy to walk 200m to the church, if his average speed was 1.6m/s? = 125seconds

11. Car graphing activity – animation

12. Distance–time graph

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

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? 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

15. Speed experiment – instructions total distance average speed = total time 1. Time how long it takes you to run 100m. 2. Then calculate your average speed for the run. 3. Repeat the experiment for each member of your group. 4. What was the fastest average speed for your group?

16. Speed experiment – results Name distance (m) time (s) average speed (m/s) 100 100 100 100 100 Conclusion The fastest member of the group, with an average speed of ___________, was _____________.

17. Speeding up vs slowing down

18. Homework What is the top speed of your car? What features does it have to enable it to have this speed? Add to your Scrap book.

19. Speed Criteria A C E Starter – Describe how your car over comes/uses the forces acting upon it… Use your research to help you

20. Acceleration Criteria A C E

21. What is acceleration? The acceleration is the rate in which an object slows down or speeds up. A train accelerates in a straight line from rest. As it does, its velocity increases. The brakes on this motorcycle are causing it to slow down. This is negative acceleration or deceleration.

22. change in speed time taken acceleration = How is acceleration calculated? The acceleration of an object can be calculated using this equation: • Change in speed is measured in metres per second (m/s). • Time taken is measured in seconds (s). • Acceleration is measured in metres per second per second (m/s2).

23.   s a = t x Using a formula triangle A formula triangle helps you to rearrange a formula. The formula triangle for acceleration (a), speed (s) and time (t) is shown below. Cover the quantity that you are trying to work out, which gives the rearranged formula needed for the calculation. So to find acceleration (a), cover up a… …which gives the formula…

24. change in speed time taken acceleration = 60 4 = Acceleration problem A racing car accelerates from rest to a speed of 60m/s in a time of 4 seconds. What is the acceleration of the car? = 15m/s2

25. change in speed time taken acceleration = 20 10 = change in speed acceleration time taken = Acceleration problem A hungry cheetah spots a gazelle and decides to chase it. The cheetah accelerates at 10m/s2 from rest until it reaches 20m/s. How long did this take? = 2s

26. Acceleration problems calculations

27. Homework Acceleration of your car? How fast can it go 0-60? 0-100? Add to your Scrap book.

28. Acceleration Criteria A C E

29. Reaction Times Criteria A C E

30. Reaction Time The time it takes you to respond to a stimulus. e.g. time between seeing a red light and applying the brakes. Under test condition, reaction time is approximately 0.75 s In real conditions it’s about 1 s

31. Reaction Distance The distance the car travels in this time.

32. Stopping Distances Criteria A C E Starter – Why do we have speeding limits

33. Speed and Safety Why are speed limits important?

34. stopping distance = thinking distance + braking distance Why have speed limits? Speed limits are an important part of road safety. They aim to prevent drivers from driving at speeds that are unsuitable and unsafe. The speed limit of a particularroad depends on a range offactors, such as how straight or curved it is, and its location. The faster a vehicle is driving, the longer it will take to stop – the overall distance this takes is the stopping distance.

35. Stopping Distance How long does it take a moving vehicle to stop?   Thinking distance is the distance a car travels before the brakes are applied. The stopping distance is the sum of the thinking distance and the braking distance. Braking distance is the distance a car travels whilst the brakes are being applied. Braking distance Thinking distance Stopping distance Stopping distance = thinking distance + braking distance

36. Can you match up the words with their definitions? One of the forces the road exerts on the tyres as the car is stopping. The distance a car travels whilst it is braking. The distance a car travels before the brakes are applied. The sum of thinking distance and the braking distance. Stopping distance Friction Thinking distance Braking distance

37. What factors affect braking and thinking distance? Speed of car Speed of car Drugs and alcohol Road conditions Condition of tyres Tiredness Medication Condition of brakes Medication Condition of tyres Speed of car Drugs and alcohol Road conditions Tiredness Condition of brakes

38. Braking Car Question: • A car is moving along an open road. Suddenly, a sheep walks into the road. • What do we call the distance the car travels before the driver puts their foot on the brakes? • b) Name one factor that could increase the distance the car travels in this time. • c) The braking distance is 35m for the car. If the stopping distance is 50m, how far did the car travel before the driver put their foot on the brakes? Thinking distance Medication, drugs/alcohol, speed of car, tiredness Thinking distance = Stopping distance – braking distance = 50m – 35m = 15m

39. Car Graphing Activity See teacher’s notes This graphing experiment shows a movie of a car travelling along a straight road. Copy the results table shown on the next slide and complete it as the movie is playing. Record the distance the car has travelled every five seconds. Then graph your results. Note that there are teacher’s notes, in “Notes View” on this slide.

40. Results table for Distance / Time Graph

42. 0 16 76 186 234 484 634 784 904 974 994 994 Results table for Distance / Time Graph

45. Stopping Distances

46. Stopping Distances Criteria A C E

47. other drugs and some medicines alcohol distractions, such asmobile phones tiredness speed What affects thinking distance? The thinking distance is the distance a vehicle travels in the time it takes for a driver to react to a situation and apply the brakes. What factors will affect thinking distance?

48. weather condition of tyres/brakes condition of road speed What affects braking distance? The braking distance is the distance a vehicle takes to stop once the driver has applied the brakes. What factors will affect braking distance?

49. Factors affecting stopping distances

50. How do speed cameras work? There are several types of speed camera., They use different methods to calculate the speed of a vehicle. Gatso speed cameras use radar to detect the speed of a vehicle, then take two photos (half a second apart) to provide visual evidence. Lines marked on the road indicate how far the vehicle has travelled in that time. Truvelo speed cameras are activated by pressure detector cables in the road. The cables are 10cm apart and a computer calculates how long it takes the vehicle to pass from one to another, and therefore the speed of the vehicle.