April 13, 2014
Wow your friends with this great demo! It looks like this string is dancing in slow motion and you can control the speed of its dance moves. It’s not just cool, it’s science:)
Episode 8: Dancing String
(Standing Waves part 1)
Isn’t that Great?!!!
Like I said in the video, it’s really just an illusion. That string is moving back and forth really fast and the strobe light just makes it seem like it’s moving slowly–or like it’s dancing. A strobe light is a light that flashes on and off really fast. In the dark room the video camera only “sees” the string when the light flashes on. I can adjust how quickly it flashes. So I can adjust it so that the light blinks on exactly when the string is back in the same spot it was at the last flash (even though it moved down and then back up). That makes it look like the string hasn’t moved. I can also make it flash a little slower so that on the next flash it looks like the string is just below where it started (the string moved down and then up and then down just a little more). That makes it seem like the string is slowly moving down. Or I can make it flash so that the string looks like it’s barely moving upwards. It’s the same sort of effect as when it looks like the wheels of a car on TV are spinning backwards. The first part of this video shows that illusion (you can watch the whole explanation if you want, but it does get a little math-y).
Even though the dancing part is an illusion the fact that the string doesn’t move back and forth in the middle is not–that is just cool physics…but more on that next time.
This is the first video of a series of three about standing waves. Look for the next video soon explaining the science behind them. The third video will be how to make a standing wave jiggler to impress your friends.
Get Stoked About Science!
February 10, 2014
Stomp Rockets are a ton of fun and also easy to make. This episode will show you how to make one out of PVC pipe and a 2 liter bottle. In about 15 minutes you’ll be launching rockets of your own!
Episode 6: Build a Stomp Rocket!
Stomp rockets also work because of pressure. You are creating a high pressure region in the bottle by smashing the air inside into a much smaller space. At the other end of the launcher the air in the pipe and paper rocket are at normal pressure. Air naturally wants to move from high pressure to low pressure. That moving air is what pushes on the rocket and launches it. This is similar to the earlier episode with the marshmallow cannon. In that case the air pushed a marshmallow as it went from high to low pressure. In this case the air is pushing a rocket as it goes from high to low (for those really interested in more advanced details about pressure, here’s a link to the explanation of pressure in fluids on hyperphysics).
- 2 liter bottle
- 1/2 inch PVC pipe (around 2 feet, a little more is better though)
- board for support base (around 1 foot long–a 2×4 or 2×2 works well)
- 2 hole conduit straps (from electrical area of hardware store–at least one, second one is optional for the holder)
- screws for the straps (nails could also work)
- duck tape (you don’t need much, just enough to tape the bottle to the pipe)
- card stock (it’s a good combination of light and strong)
- 90 degree PVC elbow
- 45 degree PVC elbow (optional)
- short length of 1/2 PVC pipe for the holder (optional)
- make sure your rocket body fits snugly around the launch pipe, but not so tight that it can’t slide freely.
- you may need to experiment with getting the fins on straight and how big to make them as well (you can do 3 or 4 fins)
- if your 2 liter bottle gets a hole in it (and it will eventually), just tape on a new one.
How far can you get your stomp rocket to go?! Measure the distance along the ground from where you launch to where the rocket hits the ground. Make sure you are firing it from level ground (no launching off a hill or a second story window).
There will be prizes for the top three distances, so send me a video or picture proof of your best launch.
Now, go get building the most EPIC stomp rocket you can!
PS: I’m serious about the prizes.