Physical Science Activity
Physics textbooks frequently contain problems with elevators.
Elevators represent types of motion commonly encountered - they start,
stop, and move with constant velocity. However, elevator physics
is somewhat non-intuitive. What happens to the passenger's
effective weight if standing on a scales when the elevator is
travelling with a constant speed is a bit confusing. If a ball is
dropped while the elevator is travelling at a constant speed between
floors, what will its acceleration be? Yet the explanation for
the elevator physics is very straightforward if one considers the
Newtonian Physics principles.
We will take a 1 kg mass, suspend the mass to a spring scale, and hold
the spring scale firmly against the elevator wall. We will also
use the camcorder to record the readings on the spring scale while the
elevator is ascending, descending, starting, or stopping.
- Use a 1 kg mass, suspend it by a spring balance so that it reads
10 Newton. (10 Newtons is the force of gravity pulling on the 1
kg mass). If the spring balance is positioned in an elevator and
the elevator is rising at a constant velocity, predict the reading on
the spring balance. [Note:
this should work much better using a more sensitive spring balance (250
g capacity) and a suspended mass of 100 g (1.0 Newton). ]
- More than 10 Newton
- Exactly 10 Newtons
- Less than 10 Newtons
- Predict the reading on the spring balance when the elevator is
descending at a constant velocity. (A, B, or C)
- Predict the reading on the spring balance when the elevator
starts to move upwards. (A, B, or C)
- Predict the reading on the spring balance when the elevator stops
moving downwards. (A, B, or C)
Use the camcorder on a tripod focused onto the spring balance. Be
sure that the scale on the spring balance can be read in the viewfinder
of the camcorder. Have the camcorder recording while the elevator
starts, moves up or down between floors, and stops. Use the sound
track to give verbal cues as to that the elevator is doing.
Ascending, descending, starting and stoping in both directions gives
six combinations for a particular motion (two more than the
prediction). Be sure to record all six motion states.
Repeat if necessary.
Examine the film and soundtrack of the elevator experiment and reach a
conclusion based on the observations.
Explain the conclusion based on Newton's 2nd law of motion.
Write the discussion in a journal entry (not a lab report). Due
date to be posted.