Homework Help: What happen if the normal reaction force is less than zero ?

1. Jul 1, 2015

goldfish9776

1. The problem statement, all variables and given/known data
why the object will fall of when the normal reaction force is less than zero ? P/s : the normal reaction force is in downward direction...
How if if the normal reaction force is less than zero ? the normal reaction is in upward direction ?

2. Relevant equations

3. The attempt at a solution

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2. Jul 1, 2015

andrevdh

The track can only push the object away, not pull it towards it.

3. Jul 1, 2015

goldfish9776

I still don't understand why when the normal reaction force is less than zero , the object will lose contact with the track ?

4. Jul 1, 2015

andrevdh

N is the normal reaction force from the track.
If the object is not pushing against the track
then it lost contact with it!
Which means it is falling.
So if N is upwards, or negative, which is impossible
since it cannot pull the object towards it, then the object
is falling. In the limiting case where it as the ppoint of leaving the
track N = 0. At this point it is "floating" and wants to leave the track
or at the point of falling since the only force on it is gravity or its weight.

5. Jul 1, 2015

goldfish9776

If the object is pushing against the track ,the object will surely losing contact with the track right , the object would fall of ?

6. Jul 1, 2015

andrevdh

No, if the object is pushing against the track then it means it is supported by the track.
Just like if you stand on the floor you push against it and it supports you with the normal force.

7. Jul 1, 2015

goldfish9776

Ok, I think I can understand it....