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Aim: How can we solve free fall problems?

Aim: How can we solve free fall problems?. Do Now: A textbook and a metal sphere fall from the same height at the same time. Which one hits the ground first?. Gravity – the natural force of attraction in the universe Gravity causes objects to accelerate

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Aim: How can we solve free fall problems?

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  1. Aim: How can we solve free fall problems? Do Now: A textbook and a metal sphere fall from the same height at the same time. Which one hits the ground first?

  2. Gravity – the natural force of attraction in the universe • Gravity causes objects to accelerate • The acceleration due to gravity is a constant near the surface of the Earth for all objects The elephant and penny hit the ground at the same time because the acceleration due to gravity is a constant

  3. Demo: 2 pieces of paper

  4. What about crumbled and flat paper? • Demo • Air resistance makes certain objects fall at different rates The elephant and feather hit the ground at the different times because of air resistance

  5. What about in a vacuum (no air resistance)? • Demo • In a vacuum, all objects fall at the same rate • If you travel high in the mountains or go to the moon, the acceleration due to gravity has a different constant

  6. Apollo 15 Video

  7. Water Droplets with a Strobe light http://www.youtube.com/watch?v=rvY7NGncCgU

  8. What’s Really Happening

  9. Free Fall Problems • With all free fall problems, we know two things immediately: • The object is dropped from rest • vi = 0 m/s • 2. Acceleration is due to gravity • a = g = 9.8 m/s2 • Solve the problem using the appropriate formula

  10. Sample Problems • An object is dropped from a height of 2 m. • a. How long does it take to reach the ground? • Given • vi = 0 m/s • a = g = 9.8 m/s2 • d = 2 m • t = ? d = vit + ½at2 2 m = (0 m/s)t + ½(9.8 m/s2)t2 2 = 4.9t2 4.9 4.9 t2 = 0.4 t = 0.6 s

  11. b. How fast is it moving when it hits the ground? Given vi = 0 m/s a = g = 9.8 m/s2 d = 2 m t = 0.6 s vf = ? vf = vi + at vf = 0 m/s + (9.8 m/s2)(0.6 s) vf = 5.9 m/s

  12. 2. An object falls off a bridge and takes 2.5 s to hit the water below. a. How high is the bridge? Given vi = 0 m/s a = g = 9.8 m/s2 t = 2.5 s d = ? d = vit + ½at2 d = (0 m/s)(2.5 s) + ½(9.8 m/s2)(2.5 s)2 d = 30.6 m

  13. b. How fast is it moving when it hits the ground? Given vi = 0 m/s a = g = 9.8 m/s2 t = 2.5 s d = 30.6 m vf = ? vf = vi + at vf = 0 m/s + (9.8 m/s2)(2.5 s) vf = 24.5 m/s

  14. Pages 68-71

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