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## Speed

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**Speed**D. Crowley, 2007**Speed**• To be able to calculate speed, and to be able to predict how the forces acting upon an object will affect the speed**Question**• Some year sevens ran to the end of the field • How fast were they running at? • What extra information would you need to answer this question?**What is Speed?**• What is speed? • What is it measured in? • How can we work out someone’s speed? • You have five minutes to discuss with your partner the above questions…**Speed**• Speed is a measurement of how quickly something is traveling at, which can be in m/s; km/h; mph; cm/year etc… • To work out the speed of something, you need to know the distance covered and the time it took to get there • So speed = distance / time • E.g. 30mph = 30 miles traveled in 1 hour • E.g. 10m/s = 10 meters traveled in 1 second • E.g. 1cm/year = 1 centimeter traveled in 1 year**Speed Formula**Distance (d) Speed (s) Time (t)**Examples**Distance Speed Time • Jack ran 100m in 12 seconds. What speed was he traveling at? • Jack then ran 100m again, but this time it was much more windy, and it took him 15 seconds. What was his new speed, and why was this different? • My car was going at 50mph for 1 hour. How many miles did I travel • My car was going at 50mph, and I traveled 20 miles. How long did this take me?**Examples**Distance Speed Time • Jack ran 100m in 12 seconds. What speed was he traveling at? Speed = 100 / 12 = 8.34m/s • Jack then ran 100m again, but this time it was much more windy, and it took him 15 seconds. What was his new speed, and why was this different? Speed = 100 / 15 = 6.67m/s (more air resistance) • My car was going at 50mph for 1 hour. How many miles did I travel Distance = 50 x 1 = 50mph • My car was going at 50mph, and I traveled 20 miles. How long did this take me? Time = 20 / 50 = 0.4 hours (24 minutes)**Speed**• How can we measure which is fastest – running backwards, running sideward; skipping or running normally? • Produce a results table to collect your speed data for the four different running styles**Speed**• Using your data work out your speed (from the average time) and graph your results... Speed = Distance ÷ Time • Your graph should be a bar graph as the data we have is categoric – it falls into distinct groups**Forces & Speed**• How do forces affect speed? • What happens when you travel very quickly (i.e. on a motorway in the car) • What is it so much effort for a rocket to take off into space? • Why is it more fun to be going downhill on your bike, rather than uphill?!**Forces & Speed**• Forces can affect speed, both positively and negatively • Forces can help move objects, i.e. a car engine delivers a force to turn the wheels of a car, moving it • For example, cycling downhill is easier than uphill as gravity is helping pull you down Bike 1 traveling steadily at 10mph - engine is working against slight air resistance Bike 2 traveling steadily at 100mph - engine is working very hard against large air resistance**Forces & Speed**• The opposite is true of space rockets, which must fight gravity to escape the Earth • As you go very quickly you also experience more friction (increased air resistance, which causes you to slow down) • Different surfaces also have more / less friction - think about what is easier to run on, carpet or ice? Bike 1 traveling steadily at 10mph - engine is working against slight air resistance Bike 2 traveling steadily at 100mph - engine is working very hard against large air resistance