Download 6.1.L Elevator Lab - White Plains Public Schools

Name: ______________________________
Physics
Date: _______________
Elevator Lab
Objective: Determine what effect going up and down in an elevator has on your “weight.”
Hypothesis: What will happen to the scales reading when you go up? Down? Remain at constant speed? Why?
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Background Information:
In order for an object to accelerate, there must be a net force (ΣF) acting on it. We know that the direction of the
acceleration will be in the same direction as the direction of the net force. The equation for Newton’s 2nd law is ΣF = ma
or a = ΣF/m.
Today we will be looking at the acceleration of an elevator when it starts and stops.
Since acceleration and force are vector quantities, we must distinguish between up
and down. Our sign convention will be positive for up and negative for down.
Therefore the force of gravity, Fg is negative and the force exerted by the elevator, FN is
positive. FN is your “apparent weight” measured by the bathroom scale you
will be standing on while the elevator accelerates. Since there are only 2
forces acting on you in the elevator, the net force, ΣF is just the vector sum of
the 2 forces (your Weight and the Normal Force as shown in the diagram).
FN (+)
Fg (-)
Observations: Place a check in each box for “Scale Reading” and “How did you feel?” as you go up and down in the
elevator. Please note that the needle will jump when the doors close, and again when the elevator locks into place after
coming to a stop. Record your observations when you feel yourself start moving, moving at constant speed, and when
you start slowing down. These moments will happen very fast, so make sure you are observant!
Going Up
Decreased
Scale Reading
Same
Increased
“Heavier”
How did you feel?
Normal
“Lighter”
Start going up
Constant
speed up
Slowing down
to a stop
(Take a moment to place checks in their boxes before coming back down)
Going Down
Start going
down
Constant
speed down
Slowing down
to a stop
Scale Reading
Decreased
Same
Increased
How did you feel?
“Heavier”
Normal
“Lighter”
Analysis
1. Draw a free body diagram for each situation. Then say whether the net force was pointing up, down, or 0 N.
Going Up
Start Going Up
ΣF =
Constant Speed Up
ΣF =
Slowing Down to a Stop
ΣF =
Going Down
Start Going Down
ΣF =
Constant Speed Down
ΣF =
Slowing Down to a Stop
ΣF =
1. Did your actual weight change when you were accelerating in the elevator? Explain why or why not.
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2. Why does the needle move when you accelerate in the elevator?
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3. In your own words, define “apparent weight.”
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4. If the cable snapped and the elevator went into free-fall, what would the scale read? Explain your answer.
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Questions:
1. A student standing in a stationary elevator has a mass of 70 kg.
a. Draw a Free Body Diagram of this situation.
b. What is the weight of the student? __________
c. What is the net force acting on the student? __________
d. What is the normal force acting on the student? __________
2. The elevator accelerates upward at a rate of 2 m/s2.
a. Draw a Free Body Diagram of this situation.
b. What is the net force acting on the student (magnitude and direction)? __________
c. What is the normal force (apparent weight) acting on the student? __________
d. Does the student feel lighter or heavier than they would normally? __________
3. Then the elevator moves upward at a constant velocity.
a. Draw a Free Body Diagram of this situation.
b. What is the net force acting on the student? __________
c. What is the normal force acting on the student? __________
d. Does the student feel lighter or heavier than they would normally? __________
4. Then the elevator slows down to a stop at a rate of -2m/s2.
a. Draw a Free Body Diagram of this situation.
b. What is the net force acting on the student (magnitude and direction)? __________
c. What is the normal force (apparent weight) acting on the student? __________
d. Does the student feel lighter or heavier than they would normally? __________
5. (2014 Regents Question) A 750-newton person stands in an elevator that is accelerating downward. The
upward force of the elevator floor on the person must be
a. Equal to 0 N
b. Less than 750 N
c. Equal to 750 N
d. Greater than 750 N