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*From*: John Denker <jsd@av8n.com>*Date*: Thu, 06 Nov 2014 09:13:47 -0700

On 11/06/2014 07:45 AM, Paul Nord wrote:

Rather than defining a new term, you just use delta p. That makes

sense.

That's how I've always done it, and always seen it done.

momentum symbol: p

impulse symbol: Δp ... no new or special symbol required

From that point of view, the relationship between impulse andmomentum is not even a "theorem" -- the only new thing here

is the definition of impulse.

We teach F = ma but we don’t seem to carry that forward to talk about

the change in velocity

I don't see impulse as a second law issue, but rather a

third law issue.

There is a pedagogical principle that says "ideas before

names" i.e. "concepts before terminology".

You can introduce the /idea/ of impulse just fine without

mentioning word; just treat it as a direct application of

the third law. Later the term "impulse" can be introduced

and attached to the idea.

==========================

My children had a 4th grade textbook with the following review question:

It takes a lot of ____ to stop an airplane.

The only reasonable choice was Force.

That's terrible. Good pilot technique calls for *not*

using a lot of force, unless needed for some exceptional

reason ... for the same reason that Driver's Ed teaches

you not to charge up to a stop light and slam on the

brakes. A panic stop causes extra stress on the structure

and (!) on the passengers.

Very few passengers have ever seen a maximum-effort

stop. They would be impressed, and not in a good way.

I assume this was a multiple-guess question. Otherwise

"distance" would be no worse than "force" ... and in

fact we know that long runways are required. Distance

and force go together, because there is energy involved.

Similarly "time" would be no worse than force. Time

and force go together, because there is momentum i.e.

impulse involved.

General rule: Pay attention to the conserved quantities!

The arriving airplane has a lot of energy and a lot of

momentum that need to be unloaded.

The correct answer is Impulse.

Impulse would be correct, but not uniquely so. Energy

would also work (so to speak).

**References**:**[Phys-L] The Impulse Momentum Theorem***From:*Paul Nord <paul.nord@valpo.edu>

**Re: [Phys-L] The Impulse Momentum Theorem***From:*Chuck Britton <britton@ncssm.edu>

**Re: [Phys-L] The Impulse Momentum Theorem***From:*Paul Nord <paul.nord@valpo.edu>

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