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 + N – W = ma a N = W + ma - So you feel heavier W

The elevator starts accelerating downward? The acceleration is downward so the net force is downward N - a + Fnet = ma W – N = ma N = W - ma So you feel lighter W

OH NO… the cable breaks… The acceleration is downward so the net force is downward Fnet = mg - a + 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/watch?v=2V9h42yspbo

The source of the nickname, of course, should be apparent. 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/watch?v=wSTLBc-4q60

In 2005, NASA replaced the aircraft with a McDonnell Douglas C-9 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 AMARC storage facility in Arizona. http://www.youtube.com/watch?v=8JC6dci06Gc

Otis L. Evaderz is conducting his famous elevator experiments 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.

N Fnet = ma N – W = ma + a - N = W + ma N = 1000 N +100 kg(.5m/s2) a. What is the scale reading when Otis accelerates upwards at 0.50 m/s2?   N Fnet = ma N – W = ma + a -   N = W + ma N = 1000 N +100 kg(.5m/s2) N = 1050 N W

b. What is the scale reading when Otis is traveling upward at a constant velocity of at 2 m/s? 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. Otis stops at the top floor and then accelerates downwards at a rate of 0.50 m/s2. What does the scale read? 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?

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