# Rotating Candles

Now this next experiment is a little dangerous (we’re going to be spinning flames in a circle), so I found a video by MIT that has a row of five candles sitting on a rotating platform (like a “lazy susan”) so you can see how it works.

The candles are placed inside a dome (or a glass jar) so that when we spin them, they aren’t affected by the moving air but purely by acceleration. So for this video above, a row of candles are inside a clear dome on a rotating platform. When the platform rotates, air inside the dome gets swung to the outer part of the dome, creating higher density air at the outer rim, and lower density air in the middle. The candle flames point inwards towards the middle because the hot gas in the flames always points towards lower density air. Source: http://video.mit.edu

Now you’re beginning to understand how an object moving in a circle experiences acceleration, even if the speed is constant.

So what direction is the acceleration vector?

It’s pointed straight toward the center of that circle.

Velocity is always tangent to the circle in the direction of the motion, and acceleration is always directed radially inward. Because of these two things, the acceleration that arises from traveling in a circle is called centripetal acceleration (a word created by Sir Isaac Newton). There’s no direct relationship between the acceleration and velocity vectors for a moving particle.

5 Responses to “Rotating Candles”
1. Aurora says:

Update – they didn’t move it.. it still works! It took a long time for the video to start, though. Try clicking on the video itself while it’s “spinning” – that sometimes works to bump it so it starts playing.

2. Aurora says:

That’s strange – the video should be unlocked for everyone, since it’s from MIT. Let me see if they moved it again.

3. bac051201 says:

I have the same problem as Karen Daley. I don’t know if I don’t have access to this content, but I can’t watch the video

4. Aurora says:

Sorry about that! Sometimes videos linked from other sites move, so thanks for letting me know. I’ve updated this link so now it’s working.

5. Karen Daley says:

We’re having trouble finding the video for Rotating Candles. We went to the YouTube channel website listed above (http://video.mit.edu )–very cool place!, but weren’t able to find the video. We’ll keep trying.