Re: [Phys-L] inertia and the tablecloth demo

[John Denker <jsd@av8n.com>]

On 08/17/2016 11:22 AM, stefan jeglinski wrote:

> I think this is largely my objection to the tablecloth experiment.
> While both this example and the tablecloth can be discussed in the
> context of inertia, I don't think there's much there for the student

I have a similar objection.  I might state it even more strongly:
  I don't have much use for the notion of "inertia".
  I have no interest in demonstrating "inertia" or even mentioning it.
  I prefer standard physics concepts such as /mass/ and /momentum/.

To demonstrate mass, go outside and push a car (with suitable
safety precautions).  Tell students, this is what a megagram
feels like.

This is a real-world topic.  I've pushed plenty of cars in my time,
e.g. when somebody's car breaks down in the middle of an intersection.

This also demonstrates momentum.  By applying a large force over
a long time, you can transfer quite a lot of momentum into the
car.  If you want to stop the car, you need to provide a comparable
amount of force for a comparable amount of time.  Use ropes, so
students can get a feel for this, without getting in front of a
moving car.

My preferred technique is to put my back against the car and push
with my legs, not using my arms at all.  I haven't found a video 
of this technique.  Perhaps somebody should make one.

There are hundreds of generic car-pushing videos, but I haven't
seen any that emphasize the physics.  Mostly they seem to be
doing it in inefficient ways, just to get some exercise.

See also next message.