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Aim: How can we explain the motion of elevators using Newton’s 2 nd law?

Aim: How can we explain the motion of elevators using Newton’s 2 nd law?. F = 150 N. Do Now: What is the acceleration of this object?. m = 20 kg. F Net = ma 150 N – 100 N = (20 kg)a 50 = 20a 2.5 m/s 2 up = a. F = 100 N. Elevator Problems. F N = Normal Force (scale reading).

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Aim: How can we explain the motion of elevators using Newton’s 2 nd law?

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  1. Aim: How can we explain the motion of elevators using Newton’s 2nd law? F = 150 N Do Now: What is the acceleration of this object? m = 20 kg FNet = ma 150 N – 100 N = (20 kg)a 50 = 20a 2.5 m/s2 up = a F = 100 N

  2. Elevator Problems FN = Normal Force (scale reading) A man is standing on a scale while in an elevator What forces exist? Fg = Weight = mg

  3. While the elevator is at rest Objects at rest: FNet = 0 Forces are balanced Fg = FN While the elevator is moving with a constant velocity Objects moving with a constant velocity: FNet = 0 Forces are balanced Fg = FN

  4. A 50 kg man is standing on a scale in an elevator while it is at rest. How much does he weigh? Fg = mg Fg = (50 kg)(9.8 m/s2) Fg = 490 N What does the scale read? FNet = 0 FN = Fg FN = 490 N

  5. The elevator now accelerates up at 2 m/s2 What does the scale read? FNet = ma The object will always accelerate in the direction of the larger force FN is larger FN – Fg = ma FN – 490 N = (50 kg)(2 m/s2) FN – 490 = 100 FN = 590 N FN = ? I feel heavier!!! This is your apparent weight Fg = 490 N

  6. The elevator now accelerates down at 1 m/s2 What does the scale read? FNet = ma The object will always accelerate in the direction of the larger force Fg is larger FN - Fg = ma FN - 490 N = -(50 kg)(1 m/s2) FN - 490 N = -50 N FN = 440 N FN = ? I feel lighter!!! Fg = 490 N

  7. The elevator now moves with a constant velocity of 3 m/s up. What does the scale read? FN = ? I feel normal!!! FNet = 0 FN = Fg FN = 490 N Fg = 490 N

  8. The elevator now is in free fall. What does the scale read? FNet = ma The object will always accelerate in the direction of the larger force Fg is larger Fg – FN = ma 490 N – FN = (50 kg)(9.8 m/s2) 490 – FN = 490 FN = 0 N FN = ? The person seems weightless Fg = 490 N

  9. Spinning in Zero Gravity

  10. What is the acceleration of the elevator? FNet = ma The object will always accelerate in the direction of the larger force FN is larger FN – Fg = ma 980 N – 630 N = ma 350 = 64.3a a = 5.4 m/s2 up FN = 980 N Fg = mg 630 N = m(9.8 m/s2) m = 64.3 kg Fg = 630 N

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