What would happen if you jumped right when it started going down?
Would the ceiling hit your head? Ouch!
Do you stay suspended in the air while the elevator plummets down?
Let's examine the elevator problem one step at a time.
First, consider a scale.
You know, the kind of scale you weigh yourself on.
When you step on a scale to weigh yourself,
there are two forces involved.
One, gravity pulls you down.
Two, the scale pushes you up.
What? You didn't know a scale could push?
Of course it can! If it didn't push up on you, you would go crashing through the floor.
This upward push is called the normal force and yes, it is normally there.
Since you're just standing there on the scale, you're not moving.
Therefore, you're not accelerating.
Newton's second law of motion -- net force equals mass times acceleration --
tells us that if the acceleration equals zero, the net force must equal zero.
Which means that the force of gravity pulling you down must be equal to the force of the scale pushing you up.
Now let's suppose you're standing on that scale in an elevator.
At first, the elevator is standing still,
so you and the scale are standing still.