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Re: [Phys-l] [PTSOS] anvil and sledgehammer inertia demo

Ahh, but the students will interpret this in an Aristotelian fashion. The
important one is going at constant speed, and they will say that the push on
the car is greater than the air resistance to keep it going 60.

Students will not perceive the annular puck demo either. It sounds good,
but is not very convincing.

There are some demos that work, but the students have to be absolutely
convinced that the forces are non zero and balanced. Come on, if you read
the research you will know some. You have to start with a situation where
the students know the answer. The air track with no horizontal forces is
one where they will say, OK, but it will not attack the balanced forces
example.

And yes there is an answer to this puzzle.

John M. Clement
Houston, TX



On Sep 29, 2010, at 3:15 PM, Stefan Jeglinski wrote:

The really important demo is to show that a moving object
with balanced forces remains in constant motion.

I substantially agree. What are your favorite demos of this, suitable
for a classroom?

The first thing that came to my mind was driving a car horizontally. I
press the gas pedal too strongly and the car accelerates; I press it
much less strongly and the car slows down.


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