1. Elevator Magic

2. What forces do you feel in an elevator?

3. What forces do you feel in an elevator?
Gravity (down)

4. What forces do you feel in an elevator?
Normal Force (up)
Gravity (down)

5. What forces do you feel in an elevator?
What you really feel is the normal force.
Normal Force (up)
Gravity (down)

6. Or at least, you cannot feel gravity without the normal force.
Although you can notice its effects.
(Oops! Next time I will remember to get in the elevator car. Oh. There won’t be a next time.
Gravity (down)

7. What forces do you feel in an elevator?
What you really feel is the normal force equal to your weight = mg.
Normal Force (up)
Gravity (down)

8. What forces do you feel in an elevator going up?
Close your eyes – do you feel heavier or lighter?
Going up!
Normal Force (up)
Gravity (down)

9. What forces do you feel in an elevator going down?
Close your eyes – do you feel heavier or lighter?
Normal Force (up)
Going down!
Gravity (down)

10. You feel heavier in an elevator going up – why?
You have both of the same forces as before.
Upwards acceleration
Normal Force (up)
Gravity (down)

11. You feel heavier in an elevator going up – why?
You have both of the same forces as before.
You also experience the acceleration of motion – ma – as long as you are accelerating.
You experience this as more weight – because the normal force is what is pushing you.
Upwards acceleration
Normal Force (up)
Gravity (down)

12. You feel heavier in an elevator going up – why?
You have both of the same forces as before.
Your weight is now mg + ma
Upwards acceleration
Normal Force (up)
Gravity (down)

13. Going down you feel lighter
- The extreme case is when you are accelerating down at equal to or faster than g – you feel no weight because you are no longer feeling a normal force from the floor!
Accelerating downward at a = g
Gravity (down)

14. If you are accelerating down at a < g, your weight is mg - ma
Accelerating downward at a < g
Normal Force (up) is mg - ma
Gravity (down)