Re: [Phys-l] gravitational force

[Ludwik Kowalski <kowalskil@mail.montclair.edu>]

On Oct 31, 2006, at 2:04 PM, Scott Goelzer wrote:

> Hi Mike,
> Not for real, but still fun.
>
> I use a solar system simulator (such as Gravitation 5.0 (?) for the
> Mac) and have the students tweak a planet's velocity and radius until
> they achieve circular orbit - its takes students forever to realize
> that the velocity must be tangent. Then the local G for the simulator
> can be calculated from Newton's synthesis. In many simulators, it's
> not the real value of G. Now, with G,  they can compute the
> velocities and radii for the planets (4 or 5) in a stable solar
> system and derive a nice linear T^2 vs r^3 plot from data obtained.
>
> Elliptical orbits can also be set up, allowing the Law of Areas
> explored. I do not go too far with this mathematically at the HS level.
>
> It is also a great introduction to perturbation since most initial
> student solar system designs accrete into a single blob.
>
> For a fake lab, it makes for a great couple of periods - better than
> movies or me drawing spastic ellipses on the board with triangles
> inside them.

Scott's message appeared as soon as my was sent. Let me mention that a 
pendulum trajectories can be filmed from below. This shows elliptical 
and circular orbits when the bob is initially pushed sidewise.

Ludwik Kowalski
Let the perfect not be the enemy of the good.