Physical Science Activity

Elevator Physics

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.

Introduction

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.

Prediction.

  1. 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). ]
    1.  More than 10 Newton 
    2. Exactly 10 Newtons
    3. Less than 10 Newtons
  2. Predict the reading on the spring balance when the elevator is descending at a constant velocity. (A, B, or C)
  3. Predict the reading on the spring balance when the elevator starts to move upwards. (A, B, or C)
  4. Predict the reading on the spring balance when the elevator stops moving downwards. (A, B, or C)

Experiment.

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.