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Example: Weightlessness

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Wize University Physics Textbook (Master) > Newton's Laws of Motion: Forces and Dynamics

Normal Force

3 Activities

Consider an accelerating elevator. (If the elevator is accelerating, is there a net force on the elevator?) A 50 kg person is standing on a scale in the elevator.

a) What would be the reading on the scale if it was not accelerating?
b) What would be the reading on the scale if the acceleration was 3.0 m/s2m/s^2upward?
c) What would be the reading on the scale if the acceleration was g downward?

The "reading" is called the apparent weight. If you are ever asked about apparent weight, you are actually finding the normal force (it is the normal force that determines what the weight would say on a scale), and dividing the normal force in that scenario by the gravitational acceleration (N=m/g).

The last case is what the concept of weightlessness refers to. The person still has mass, of course, but the concept of weight comes from the normal force.

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More Normal Force Questions:
A 45 kg45\ kg man is standing in an elevator. Find his apparent weight in each case: (that is, find the normal force on the man in each case):
a) The elevator is traveling steadily at 3.0ms3.0\frac{m}{s}
b) The elevator is still.
Ferris wheel
A 65 kg man is riding a Ferris wheel with radius of 15 m, that moves at speed 2.355 m/s. Determine the normal force that the man experiences at the top of the ferris wheel and at the bottom.
A 45 kg45\ kg man is standing in an elevator. Find his apparent weight in each case: (that is, find the normal force on the man in each case):
a) The elevator is traveling steadily at 3.0ms3.0\frac{m}{s}
b) The elevator is still.
A person with a 50 kg50\ kgmass is standing on a scale in an elevator which moving upward.
a) What is the reading on the scale when the elevator moves upward with a constant velocity of 10 m/s10 \ m/s?
b) The elevator is going to stop with a deceleration of 4.0 m/s24.0 \ m/s^2. What is new reading on the scale?
Dave is standing on a scale in a descending elevator for some reason. As the elevator is moving at a constant velocity, the scale reads 85kg. As the elevator approaches his floor, it starts to decelerate at 4m/s2. What does the scale read now?
Two tennis players are rallying a tennis ball.
Describe the forces (draw a FBD) on the ball when it is:
a) In flight
A 45 kg45\ kgman is standing in an elevator.
Draw a free body diagram of the system then find the normal force and the apparent weight of the man for the following cases.
a) The elevator is traveling steadily at 3[ms]3\left[\frac{m}{s}\right]
Forces: Normal force
A person is standing on a scale in an elevator. How does the reading of the scale changes when the elevator is stationary, moving with a constant speed up, and is accelerating downward?
Note! The same question can be asked by a mass hanging on a spring in an elevator.
Normal force
A man pulls 200Kg crate with rope angles 30 o above the horizontal with force 200N. The crate sits on the frictionless surface. Calculate the normal force. Enter answer in N.