Barometer

1
Barometer

• Or, THERE ARE MANY CORRECT WAYS TO ANSWER A TEST
  QUESTION

2
Story background

• A physics teacher was about to give a student a
  zero for his answer to a test question.
• The student claimed that he would receive a 100,
  if the system were not so biased against him.
• Teacher and student agreed to submit the issue to
  a mediator.

3
The test question was

• How to determine the height of a very high
  tower with the aid of a barometer? "

4

• An idea ?

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The student's answer was

• Take the barometer to the top of the tower,
  attach a long rope to it, and lower the barometer
  to the ground.
• Pull it up, measure Lrope and Lbarometer.
• Ltower Lrope Lbarometer

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The mediator ruled that

• The student really had a case for full credit
  since he had answered the problem completely and
  correctly.
• Yet, full credit should certify that the student
  learned his physics, as confirmed by the answer.

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Mediators resolution

• The student will have another try at answering
  the question.
• This time the answer should indicate some
  knowledge of physics.
• After some minutes, the student said that he had
  several answers and he was thinking which would
  be the best.

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• Any idea ?

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Then, the student went

• Take the barometer to the top of the tower. Lean
  over the edge of the roof, drop the barometer,
  time its fall with a stopwatch.
• Use H1/2 g t2 to calculate H.
• The teacher agreed to give the student nearly
  full credit.

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• Any idea ?

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As the student had other answers, we asked him
what are they

• Take the barometer out on a sunny day and measure
  the height of the barometer, the length of its
  shadow, and length of the tower's shadow, then
  use simple proportion to determine the height of
  the tower.

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and more

• Take the barometer and begin to walk up the
  stairs. As you climb, you mark off lengths of the
  barometer along the wall. You then count the
  number of marks to get the height of the tower in
  barometer units.

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and more

• Tie the barometer to the end of a string, swing
  it as a pendulum, and determine the value of 'g.'
  The height of the tower can, in principle, be
  calculated from this.

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and more

• And.. without the limit of physics, you can take
  the barometer to the engineering department of
  city hall.
• There, tell the engineer, that you have a fine
  barometer, and hell get it as a present, for
  telling you the height of the tower.

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Finally, the student admitted that he even knew
the textbook answer

• Measure the air pressure at the bottom and top of
  the tower
• Apply the formula illustrating that pressure goes
  down as height goes up.
• but he was so fed up with teachers who expect
  only formal answers, that he decided to rebel.

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Summary

• The teacher seriously considered changing the
  students grade to full credit.
• The End