How could we predict what kind of shadow we'll get?
We listed variables that might help determine the shadow size and/or composition:
- Bulb/ball distance (our objects were balls)
- Ball/wall distance (the shadows were cast on walls)
- Bulb size
- Ball size
- Bulb brightness
- Ball shape
- Bulb shape
- Alignment of ball/bulb/wall
- They decided to stick with the "normal" incandescent bulbs that we had for the moment
- We'll stick with the 2.5" styrofoam balls on little wire stands for now
- They decided that the bulb brightness wouldn't really do much, and that we didn't really have a way to vary it anyway
- We'll stick with a linear arrangement - ball, bulb, wall in a line, level with each other
Varying Ball/Bulb distance, examining shadow size
Varying Ball/Wall distance, examining shadow composition
There are some great observations here, chief among them that the relationships aren't linear. With so many variables and nonlinear relationships, we went to a digrammatic method to try to make the predictions. I didn't picture any of these, but each group was able to realize:
- Light travels in straight lines
- Shadow happens because (at least some of) the light from the bulb is blocked from reaching some location on the wall
- Not all of the light has to be blocked to make a shadow, but if it is, it'll be that dark part of the shadow
- Finding the dark part of the shadow (which we then named the umbra) wasn't too terribly difficult
- Finding where the edge of the shadow was (we called the light outer part the penumbra) was much more difficult - at this point, we had a billion rays going every which way!
- We needed a better method - one that required drawing fewer rays, for sure. That's our motivation for doing our reading tonight.