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Acceleration in an elevator

  1. Oct 29, 2006 #1
    how does the acceleration used in the formula f=ma change when the acceleration changes. you start at 9.8 m/s2. you get in an elevator or you move upward, changing the acceleration. how does acceleration due to gravity change? increase or decrease?

    thanks
     
  2. jcsd
  3. Oct 29, 2006 #2

    Office_Shredder

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    the acceleration due to gravity stays the same.

    You have two forces, the normal force, and the gravitational force. The force of gravity continues to press downard with the same magnitude, but the normal force increases. This is why you move up (Note the total force is the sum of the forces)
     
  4. Oct 29, 2006 #3
    so an upward acceleration of say, one m/s2 would just be added to g? meaning total acceleration for f=ma would be 10.8?
     
  5. Oct 29, 2006 #4

    Office_Shredder

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    No. Here's how it works. Your object starts with two forces, fg, force of gravity, and fn the normal force. The force of gravity has a downward acceleration of 9.8 m/s2, which we'll call negative because we defined the y axis to be positive pointing upwards, while the normal force starts with an upward acceleration of 9.8 This is why you don't move, because the net force Fnet = fn + fg which means:

    ma = mg + m(-g) = 0 implies a=0

    So if you accelerate upwards with a magnitude of 1 m/s2, the normal force increases so the acceleration of that force is g+1. This means
    Fnet = fn + fg gives us

    ma = m(g+1) + m(-g) = m(g+1-g) = m

    So a=1 m/22, as expected.

    I think you should talk to your physics teacher about this, because you seem to a bit confused as to what net force is
     
  6. Oct 29, 2006 #5
    that was beautiful. much thanks.
     
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