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Re: [Phys-l] g...



Call it whatever you want, but the force of Earth's gravity is the oldest
known force, the one everyone is most familiar with, and ironically, the
least understood of the fundamental forces.
So, to me, gravity is a great place to discuss/introduce acceleration. And
gravity gives us our weight, but confusion arises when we introduce a
bathroom scale. I tell my students that our "true weight" is w = mg, and
is maximum at sea level. But a bathroom scale measures your "apparent
weight." Call it the normal force or a support force, but it always points
away from the scale. So if you jump off a cliff (no air) with a scale
beneath you, it will read zero. No apparent weight, but plenty of true
weight. It is this force that makes you fall (via N2L). Also a great help
when discussing amusement park rides and and the misconceptions regarding
the "weightlessness" of the orbiting shuttle astronauts.

Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu> writes:
On 11/18/2006 05:43 PM, Paul Lulai wrote:
bringing a gun to a knife-fight.

Well, we can agree that the answer is context-dependent.

In the context of the most-naive students, there are a hundred good
reasons for not mentioning "gravity" at all ... not until they have
some clue what is a "force" and what is an "acceleration".

Gravity is not a good introductory example of force /or/ acceleration.

If the gravity question comes up, you can either duck the question
entirely, or explain it a little bit (with the expectation that they
won't 'get' it, and you'll have to explain it again later).

Some texts provide a systematic introduction to the notion of force,
and some don't. If your text jumps right in, using weight as "the"
canonical example of a force, then you've been painted into a corner.

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