An elevator is connected via a strong steel cable. While the elevator is acceler

Question

An elevator is connected via a strong steel cable. While the elevator is accelerating upwards, how does the force of the cable on the elevator compare to the force of the gravity on the elevator?

Part 2-- If your answer to the above ? was they they are equal in magnitude but opposite in diection, explain how the elevator can accelerate. Dont the equal forces add to zero?? if your answer to the above ? was that one of the forces was greater than the other one, explain why Newtons 3rd law does not apply in this case?

Explanation / Answer

yes,
tension in cable = weight of elevator
tension in cable = weight of elevator + mass of elevator x acceleration of elevator

The cable has to bear the tension not only of the normal force of gravity on the elevator car (mass in kg x 9.8 m/sec^2 N), but also the force of its upwards acceleration. e.g. if the acceleration was 5 m/sec^2, the cable tension would be the elevator car's mass x (9.8 + 5) m/sec^2 N.
The resistance force from accelerating the car, as well as its normal weight, are providing forces acting downwards, while the cable force is upwards, equal and opposite.
If the elevator were accelerating downwards at 9.8 m/sec^2, the occupants would be weightless, like being in space. It would be in free fall. Neglecting frictions, there would be no force being supplied by the cable either up or down. It may as well be detatched.

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