Re: [Phys-l] gravitational force

[Scott Goelzer <s.goelzer@comcast.net>]

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


**********************************
Scott Goelzer
Physics Teacher
Coe-Brown Northwood Academy
Northwood NH 03261
603-942-5531e218
sgoelzer@coebrownacademy.com
**********************************


On Oct 31, 2006, at 12:13 PM, Mike VanAntwerp wrote:

> Sure- thanks for the sarcasm.  I'm looking for ways to get students to
> work with Kepler's Laws and F= G (m1m2/d^2) in a lab setting.  This is
> for a high school class.
>
> Mike Van Antwerp
> Biology W202
> mvanantw@hpsk12.net
>
> > > > jsd@av8n.com 10/31 10:25 AM >>>
> On 10/31/2006 09:23 AM, Mike VanAntwerp wrote:
> > Does anyone have any lab activities or advice on teaching a unit on
> > this?  I'd appreciate any  help with this.
>
> Can you ask a more specific question?   There are probably hundreds
> if not thousands of possible lessons in this general area.  Just to
> scratch the surface:
>  -- Dropping things.
>  -- Rolling things on inclined planes, à la Galileo.
>  -- Pine car derby.
>  -- Pendulums.
>  -- Interrupted pendulums, à la Galileo.
>  -- Putting an accelerometer in a nearby elevator.
>  -- A field trip to the nearest pre-school playground merry-go-round
>   http://trouble.philadelphiaweekly.com/archives/MERRY-GO-%20ROUND.jpg
>
>  -- Centrifuges.
>  -- Centrifuges where the string is cut loose at the 12:00 position so
>   that the subsequent motion of the now-free particle can be observed.
>   Hint:  the string can be cut by a torch, or released by a photogate
>   plus electromagnet.  The idea is you want to make sure the cutting
>   process doesn't disturb the motion.
>  -- et cetera...................
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