Let’s ride on an Elevator
What happens to your weight as you ride on
an elevator?
What is your weight if
the elevator is not
moving?
We know that the
acceleration is zero.
So the net force is zero
So the upward force
of the floor (N) is
equal to your weight.
N - is the normal force
A note about
Scales ….
When the elevator starts accelerating upward?
The acceleration is
upward so the net
force is upward also
N
Fnet = ma
+
a
W
N – W = ma
N = W + ma
So you feel heavier
The elevator starts accelerating downward?
N
The acceleration is
downward so the net
force is downward
-
Fnet = ma
a
W – N = ma
+
W
N = W - ma
So you feel lighter
OH NO… the cable breaks…
The acceleration is
downward so the net
force is downward
a
+
Fnet = mg
W – N = mg
N = W - mg
N=0
W
So you feel weightless
The Vomit Comet was the
nickname given to the aircraft
used by NASA's Reduced
Gravity Research Program.
The plane makes parabolic
flight paths, allowing the
occupants to experience
reduced gravity during the
parabola. By modifying the
flight path, any value for the
apparent gravity may be
produced.
http://www.youtube.com/wat
ch?v=2V9h42yspbo
In general it is used
to train astronauts in
zero-g maneuvers,
giving them about 25
seconds of
weightlessness out
of 65 seconds of
flight.
The source of the
nickname, of course,
should be apparent.
http://www.youtube.com/wat
ch?v=wSTLBc-4q60
In 2005, NASA replaced the
aircraft with a McDonnell
Douglas C-9. One was
used for filming scenes
involving weightlessness in
the movie Apollo 13; that
aircraft was retired in 2000
and is now on display at
Ellington Field, near the
Johnson Space Center. The
other made its final flight on
29 Oct 2004, and is to be
permanently stored in the
http://www.youtube.c
AMARC storage facility in
om/watch?v=8JC6dci0
Arizona.
6Gc
1. Otis L. Evaderz is conducting his famous
elevator experiments. Otis stands on a
bathroom scale and reads the scale while
ascending and descending the John Hancock
building. Otis weighs 1000 N, but notices
that the scale readings depend on what the
elevator is doing. Use a free-body diagram
and Newton's second law of motion to solve
the following problems.
a. What is the scale reading when Otis
accelerates upwards at 0.50 m/s2?
N
Fnet = ma
+
a
-
W
N – W = ma
N = W + ma
N = 1000 N +100 kg(.5m/s2)
N = 1050 N
b. What is the scale reading when Otis is
traveling upward at a constant velocity of at 2
m/s?
D epress m o use to view answer.
c. As Otis approaches the top of the building,
the elevator slows down at a rate of 0.50
m/s2. Be cautious of the direction of the
acceleration. What does the scale read?
D epress m o use to view answer.
d. Otis stops at the top floor and then accelerates
downwards at a rate of 0.50 m/s2. What does the scale
read?
D epress m o use to view answer.
e. As Otis approaches the ground floor, the
elevator slows down (an upwards acceleration) at a
rate of 0.50 m/s2. Be cautious of the direction of
the acceleration. What does the scale read?
D epress m o use to view answer.
What is the tension in the cable if the box
has a weight of 1600N and the man 300N?
F net = (mman + mbox) a
T - Wman- Wbox= (mman + mbox) a
T = Wman+ Wbox + (mman + mbox)
a
T= 300 N + 1600 N +
(30 kg +160 kg) 0.620 m/s2
T = 2017.8 N