How to find the direction of the Net Force of an elevator?

Question

Well...I though that the direction of the net force would be up when the elevator is going up and down when the elevator is going down...but sometimes it doesn't work that way. help please I would like to know.

Answer 1

remember that FORCE = MASS X ACCELERATION.
since acceleration is vector and mass is scalar so the direction of net force will be in direction of 'net acceleration'.
when the elevator is going up then its 'velocity' is downwards not its acceleration and that is the point of mistake.check what is the net acceleration of elevator.T
if it is going down and accelerating then its acceleration is downward.So net sum of all forces will be in the downward direction.
But if it is going down and decelerating then its acceleration is UPWARD and net force will act in UPWARD direction, although the velocity is downwards.This net upward force gradually slows down the downward velocity.
similarly find for upward motion.

even if its net acceleration is horizontal while it is moving vertical net force on it is horizontal.

JUST ALWAYS REMEMBER THE THUMB RULE THAT NET FORCE IS IN THE DIRECTION OF NET ACCELERATION AND NOT NET VELOCITY AND U WILL NEVER MISTAKE.

Answer 2

There is only a net force when the elevator is accelerating.

When the elevator is accelerating upward, the net force points up.
When the elevator accelerates down, the net force points down.

When the elevator is moving at a constant speed (in any direction), or stopped entirely, there is no net force.

Force = mass * acceleration
If there is a net force, there is an acceleration. Without an acceleration, there is not a net force.

Answer 3

The net force will always be in the direction of acceleration.

So when the elevator starts to go up, it first accelerates upward: the net force is up. It then reaches a constant speed: no acceleration: net force = 0. It finally decelerates to stop: therefore, net force is in the opposite direction of motion: down.

If it is going from a top floor to bottom:
It goes from rest to going down, thus downward acceleration: downward net force.
It travels at a constant speed: no net force.
It slows down and stops, thus going from a downward motion to a stop: upward net force.

Answer 4

It may help to realize that the elevator can, and often does, have velocity in a direction opposite to it's acceleration. This happens just before a stop, regardless of whether it's stopping from an upward or downward initial velocity. By the same reasoning, just after a start, the acceleration and velocity have the same direction regardless of whether it's starting down or up.