[IAEP] Physics - Lesson plans ideas?

Gary C Martin gary at garycmartin.com
Sat Aug 15 15:29:17 EDT 2009

Hi Bill,

Not sure if you wanted answers :-)

On 15 Aug 2009, at 02:51, Bill Kerr wrote:

> I might try these next week and see how they go:
> does altering the size of an object affect its drop time?


> does joining objects together (large and small) affect drop time?


Remember, you can run all cases at once! Just pause the simulation.  
Add a box right across the horizontal middle of screen. Pin it at left  
and right edge so it's fixed. Then across top half of screen add a  
large sphere, a small sphere, a couple of linked objects. Play the  
simulation so all shapes land on the horizontal pinned box. Pause  
simulation again, and delete the horizontal pinned box. Now you're all  
set up, shapes all aligned up for their race to the ground :-) Play!

> does altering the length of a pendulum affect its swing time?


For more advanced, you might like to try a 'split pendulum', and get  
to see a slow and fast swing in one cycle (some thing like the  
attached image works fine).

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> before doing the above say what you think will happen
> after doing the above say whether you think the physics program  
> reflects real world behaviour
> (possibility of follow up real world experiments here)

"possibility of follow up real world experiments here" nice :-) +1

FWIW: Newton's cradle type set-ups don't work quite as expected (you  
end up with an oscillation of half the balls each time), I think this  
might be down to the default material properties we are currently  
using for all shapes. We have a future Physics feature to expose the  
material properties, likely a simple list of material pre-sets  
(something like "helium" "wood", "rubber", "steel", "lead").

> design a catapult system to accurately hit
> (a) stationary distant target (b) moving target (c) close target
> build a complex or elegant building that doesn't fall down

A nice one here for a challenge is to restrict the design to only use  
circles with links. Try for an Eiffel Tower like shape. It is "World  
of Goo" all over again ;-)


> other ideas along these lines?

General miscellaneous tips:

- Pretty fundamental is the need to pause the simulation when  
constructing more complicated structures (unless you make that the  
challenge, build an X without pausing the simulation).

- While paused, use shapes to help as 'construction templates' to help  
place new things accurately (they can overlap), then delete the  
template shape before resuming the simulation.

> extra features I would like to see in physics:
> copy shapes

Not on our feature list, will have a think how practical this would be  
to actually implement.

> move them while in setup mode

Been requested before already. Might be hard to implement. Don't think  
we have control over this in Physics, likely something down stream in  
either Elements, or Box2D (or all 3!).

> a timer

My call on this is related to another possible future feature. Object  
trails would be very useful (daub a blob of paint on a shape and watch  
it leave a trail on screen). This 'paint daub' could be set to pulse  
to a timer, then you could just count the trail marks.

Sound would also be great, set a specific shape to make a custom sound  
on any collision, set a shape to play a sound based on it's velocity  
(or rotation). I'd likely suggest we avoid sound until Sugar (well the  
various distros) have reliable stable sound (right now it seems a real  

> icons:
> I think it would be better if the polygon icon looked like an  
> irregular shape rather than a regular hexagon

Have this feature request already, you should get it in the next  
release :-)

> btw if there was a regular hexagon then you could use it to do some  
> work with tessellations in setup mode using the triangle, square,  
> hexagon - if you had the move feature in setup mode
> eg. make a tessellation in setup mode and then support it so it  
> doesn't fall apart under gravity

Not planning on this, but will keep it on a possible feature list.

Thanks for all the great feedback so far!!


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