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Elevator Forces

Elevator Forces. Scenario: One mass hanging. This mass is not moving. F T. ΣF = 0. ΣF= F T - w. What forces are acting on this mass?. 0 = F T - w. F T = w. F T = 1000 N. 100 kg. F g = w = mg =. 100 kg (10 m/s 2 ). Remember, even if this mass

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Elevator Forces

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  1. Elevator Forces

  2. Scenario: One mass hanging. This mass is not moving. FT ΣF = 0 ΣF= FT - w What forces are acting on this mass? 0 = FT - w FT = w FT = 1000 N 100 kg Fg = w = mg = 100 kg (10 m/s2) Remember, even if this mass was moving with a constant velocity the sum of the forces would still be zero.

  3. a This mass moving. Scenario: One mass hanging, being accelerated upward at 3 m/s2 FT ΣF = ma ΣF= FT - w What forces are acting on this mass? ma = FT - w FT = ma + w FT = 1300 N 100 kg TENSION IS MORE Fg = w = mg = 100 kg (10 m/s2) = 1000 N

  4. a This mass moving. Scenario: One mass hanging, being accelerated downward at 3 m/s2 ΣF = -ma ΣF= FT - w FT -ma = FT - w What forces are acting on this mass? FT = ma - w FT = 700 N 100 kg TENSION IS LESS Fg = w = mg = 100 kg (10 m/s2) = 1000 N

  5. Let’s look at what happens to forces and your apparent weight (FN) on an elevator. This elevator is either not moving or moving with a constant velocity. FT FN The scale reads your true weight. This is just like when the mass was hanging. 100 kg ΣF = 0 Fg = w ΣF= FN - w Fg = w 0 = FN - w FN = w

  6. On an elevator that’s accelerating we experience of a change in “weight” which is actually due to a change in the normal force, not weight (mg). Because if you think about it your weight (mg) never changes (your mass remains the same so does gravity). What happens to your apparent “weight” when an elevator accelerates upward? FT This elevator is now accelerating upward. FN This is just like when the mass was accelerating upward. Fg = w 100 kg The elevator is pushing up on you with more force, so you “feel” heavier. Fg = w

  7. This elevator is now accelerating downward. What happens to your apparent “weight” when an elevator accelerates downward? FT 100 kg FT This is just like when the mass was accelerating downward. The elevator is pushing up on you with less force, so you “feel” lighter. Fg = w Fg = w

  8. This elevator has now snapped and is accelerating downward at the force of gravity. There is no FN, the scale is falling as fast as you are, nothing is pushing on you. 100 kg This is freefall. a = g This is the feeling of weightlessness. Fg = w Fg = w

  9. Astronauts in a spacecraft orbiting the Earth or out for a “spacewalk” are seen to “float” in midair. This is sometimes referred to as weightlessness or zero gravity. Are these terms correct?

  10. An astronaut experiences as much as 8 g’s of force on blast-off because of the acceleration. This net force (experienced as apparent weight) is exerted on the astronaut by the seat which pushes on the astronaut with a force many times their weight. If the astronaut were sitting upright upon launch, such a force would cause the body to accelerate away from it’s own blood ( Newton’s 1st- object at rest…). Thus the blood appears to go to the legs, where the blood vessels and capillaries would rupture. Consequently, astronauts are in a reclining position for blast-off. FN w

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