Newton

1
Newtons Laws in an Elevator
Elevators are great devices for the study of
Newtons First and Second Laws as during a single
trip the elevator moves at constant velocity and
at other times it accelerates!
Consider a trip from the first floor up to the
10th floor.
2
Newtons Laws in an Elevator
Consider a trip from the first floor up to the
10th floor.
The complete motion might look something like
3
Newtons Laws in an Elevator
Accelerating (slowing down)
There are three parts to the motion
Constant Velocity (no acceleration)
Accelerating (speeding up)
4
Newtons Laws in an Elevator
Draw a force diagram of the rider (not the
elevator!)
Since the elevator and the rider are accelerating
upward, the net force must act upward
How would you feel? Heavier, lighter or normal?
Heavier!
You dont feel the force of gravity, rather you
feel how much the floor is supporting you!
Accelerating (speeding up)
5
Newtons Laws in an Elevator
Dont forget!
The acceleration is positive in this case because
it and the net force act upward
Accelerating (speeding up)
6
Newtons Laws in an Elevator
Draw a force diagram of the rider (not the
elevator!)
Constant Velocity (no acceleration)
Since the elevator and the rider are not
accelerating (constant velocity)
You would feel normal!
7
Newtons Laws in an Elevator
Accelerating (slowing down)
Draw a force diagram of the rider (not the
elevator!)
Since the elevator and the rider are accelerating
downward, the net force must act downward
How would you feel? Heavier, lighter or normal?
Lighter!
You dont feel the force of gravity, rather you
feel how much the floor is supporting you!
8
Newtons Laws in an Elevator
Accelerating (slowing down)
Dont forget!
The acceleration is negative in this case because
it and the net force act downward
9
Newtons Laws in an Elevator
What if you were standing on a scale while in the
elevator?
The scale supports you, so the scale would read
the Normal Force it exerts on you!
Rest Weight
Feel Lighter
Feel Heavier