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Forces 2

Forces 2. Pressure. You can not wear studded football boots indoor because the damage the floor This is because the studs have a smaller surface area than your foot. Pressure is measured in N/m 2. Objects Exerting High Pressure.

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Forces 2

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  1. Forces 2

  2. Pressure • You can not wear studded football boots indoor because the damage the floor • This is because the studs have a smaller surface area than your foot • Pressure is measured in N/m2

  3. Objects Exerting High Pressure • People have been stabbed with high heel (stiletto) shoes • Razor blades have a small surface area to exert a lot of pressure • Drawing pins have a sharp end that can exert a lot of pressure and stick into boards

  4. Spreading Out Weight • Caterpillar tracks spread out the weight of a tank • Snow boots prevent people from sinking into the snow

  5. Caterpillar Tracks The t-55 Soviet tank

  6. The Snowcat

  7. Pressure Questions • Why does a JCB have caterpillar tracks? • To spread it’s weight out and prevent it sinking into mud (Reduce it’s pressure on the ground) • If a women has a weight of 60 N and each shoe has a surface area of 10 cm². What pressure does she exert on the ground? • She has two feet so her combined surface area is 20cm². • Pressure = Force / Area • 60÷ 20 = 3 N cm²

  8. Pressure Questions • A footballer weighs 80 N and he exerts a pressure of 10 N/ cm². What is the surface area of one boot? • Area = Force/ Pressure • Area = 80 / 10 = 8 cm² ( but this is for both boots) The answer is 4 cm²

  9. Pressure Questions • The pressure the t-55 tank exerts on the ground is 91,500 N/ m². Each of the tanks caterpillar tracks are 2 m². How much does the tank weight? • Force = Pressure x Area • Force = 91,500 x 4 (A tank has two tracks) • Force = 366,000 N

  10. Speed • Speed is measured using this equation: • Units are metres/ second (m/s) or kilometres/ hour (km/h)

  11. The Blackbird (SR-71) • This stealth plane could travel at speeds of mach 3 • Mach 3 means three times faster than the speed of sound • It holds the record for the fastest plane (2,193mph) • It could travel from London to New York in under 2 hours • (An ordinary jet would take 6 hours)

  12. Speed Questions • If a sprinter runs 100 m in 10 seconds, what is his speed? • 100 ÷ 10 = 10 m/sec • If a car is travelling at 60 miles per hour for 3 hours how far does it travel? • 60 x 3 = 180 miles • If a car is travelling 30 miles per hour and it travels 120 miles how long did the journey take? • 120 ÷ 30 = 4 hours

  13. Speed Questions • A cheetah can run 460 m in 20 seconds. How fast can it run? • 460 ÷ 20 = 23 m/sec • Cheetah’s prey on gazelles. A gazelle can run for 14 km in 15 minutes. How fast is the gazelle and can it escape the cheetah? • 15 x 60 = 900 seconds • 14 km = 14, 000 m • 14,000 ÷ 900 = 15.6 m/sec • The cheetah will catch the gazelle

  14. Distance/ Time Graphs • The gradient (or slope) of the graph tells you the speed of an object • In this graph the object is not moving

  15. Distance/ Time Graphs • This graphs shows an object moving at a steady speed

  16. Distance/ Time Graphs • This graph shows an object accelerating (getting faster)

  17. Speed/ Time Graphs • These graphs show whether an object is accelerating, decelerating or travelling at a steady speed • This is a an object travelling at a steady speed

  18. Speed/ Time Graphs • This is an object accelerating

  19. Speed/ Time Graphs • This is an object decelerating

  20. Questions • What is happening in this graph? • Two objects are travelling the same distance, but the yellow line is faster

  21. Questions • What is happening in this graph? • An object is travelling at a steady speed, then it increases to a faster steady speed

  22. Questions • What is happening in this graph? • An object travels at a steady speed, then stops, then moves off at a faster steady speed

  23. Questions • What is happening in this graph? • Two objects are accelerating to the same speed, but the yellow one is accelerating quicker

  24. Questions • What is happening in this graph? • Both objects are decelerating to a stop, but the red line is decelerating faster

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