We started class today with the following videos:
And we can’t talk about the vomit comet and feeling weightless without watching OK Go.
For the lab I used Activity #4, Listen to gravity, like Galileo did, from “Gravity” a physics lab from Ellen McHenry’s Basement Workshop. Students tied washers to a piece of string, either equally spaced (50 cm) or with the distance between washers increasing (10 cm, 30 cm, 50 cm, 70 cm, 90 cm) as they tied them to the string. If you hold one end of the string up high (standing on a chair/stepstool) and let it hang to the floor, what do you think you will hear when you drop the string with equally spaced washers? Will the noises be equally spaced in time or when they the ‘dings’ get closer together as the string/washers accelerate? What about the second string with the washers spread out at increasing distances? Will the dings be further apart as the string falls, or when they will be equally spaced? After the students think about it a bit… and untangle their string of washers (this took almost as much time as tying them all on to the string) they actually drop them and listen to the pattern of sound the washers make. We dropped the string of washers on to a cookie sheet to make a nice loud ding.
The string with the equally spaced washers hit the ground at shorter and shorter time intervals since the washers that fell longer are accelerating for a longer period of time and going faster when they travel the last 50 cm before hitting the cookie sheet. The washers that were tied at greater and greater distances hit the ground at roughly equal time intervals. Here’s a slow motion video of the string with equally spaced washers.
Slow motion video of the second string, with washers at increasing distances but hitting the pan at almost equal time intervals.
Its kind of hard to hear when you’re doing the actual experiment so having someone take a movie so you can watch/listen in slow motion is useful.