EXAMPLE 4: The Elevator
Question

Our furry friend, King Kong, has had enough of monkey-ing around, and has returned to the Big Apple. Once again he is up to his tricks with the Empire State Building. Only this time, he has taken the elevator instead. While he is riding up to the top of the building, what forces are acting on him?

Hints

The forces we discussed were

1.gravity

2.normal

3.friction

4.push or pull

Solution

1. We assume that King Kong is (in the elevator in the EmpireStateBuilding in New York) on Earth, so he still experiences the Earth's gravitational force,

Fmg.

2. The overgrown gorilla is in contact with the elevator floor, so there is a

normal force N (which is not necessarily equal to Fmg)..

3. There is no static friction. This may be a bit difficult to see at first, but as we shall soon see, no force is trying to move the gorilla along the elevator floor. Since he is simply standing, then we can say there is no force due to static friction. Similarly, there is no kinetic friction.

4. No one or thing is pushing or pulling on King Kong (and who or what would want to?), so there is no push or pull force. There is no rope-like pull on this hairy monster, so no force due to tension acts on him.