Sand pendulums - Lissajous patterns - part one // Homemade Science with Bruce Yeany

yes [Music] Oh looks like a watermelon [Music] in the galaxy [Music] well I'm wearing it today I'm gonna take a look at the patterns that we can create using various setups of pendulums now we can record the results using sand or paint or even light and we can get some beautiful patterns from it so let's take a closer look now to start this we should know that as pendulums get longer its period or the amount of time it takes for one complete movement back and forth also becomes longer all right now we're going to start with the same pendulum and the materials we need are fairly simple now first of all I had this big box which and very simply I have this to contain the sand and keep it from going over all over the place but we don't necessarily need it now next we're gonna need some sand obviously this is common ordinary place and it's available at any hardware store well made some string we need a container to hold the sand this first bob was made by a friend of mine it's ceramic it has a hole in the bottom right there and it's supported at three points using strength this next one is a soda bottle I cut the bottom out of it right there and the top cap has a hole in it about an eighth of an inch I'll screw this on in place now the holder for this is made out of wood it's a ring that is supported on four sides and the bottle fits very tightly inside of it this makes it very easy to adjust its height in relation to the table now here's an even easier version the soda bottles cut off at the bottom it's got three holes in it for support strings attached to it and once again we have a hole in the cap or letting the stand out in this first instance I simply want to use a single string and attach it up to the ceiling all right now let's take a look at the movement of this pendulum along the single axes if we were to time it it takes about two and a half seconds for it to move along this single axes now if we were to move in the opposite direction it still has a period of about the same amount of time so it doesn't matter whether it's moving this way or this way it takes the same amount of time for it to complete one oscillation but what we're interested in is a combination of these two movements together so let's give this some energy either as a circle or an ellipse and see what we get at this point on speeding up the video otherwise it would take about five minutes for this pattern to be completed so our result was that we got an ellipses spiral didn't word because the pendulum was constantly losing energy to friction too it's not in the center now when we record the movement of the pendulum the result is what we call a Lisa's use pattern we could change the shape of the pattern if we could alter the periods along the two axes now how would it be possible for one pendulum to have two separate periods well part of the answers right here our next pendulum is going to look something like this two points of contact at the ceiling coming together to a single strand that comes down to our Bob now if this set up the period of this pendulum is going to depend on the direction that it's swinging if it's swinging in this direction well then the movement is from the Bob all the way up to the ceiling notice that the white and the pink string are both moving together now if it's swinging in this direction it's gonna have a period of about 2.5 seconds but if it's swinging in this direction well then the movements not going to be the whole length it's going to be from the Bob up to whether strings are connected so just the container in the white string are moving if we look up at the pink string we see in this case it's stationary now the period moving in this direction is going to be faster in fact let's time it it's about 2 seconds simply because from the Bob to where those strings are combined is a shorter distance to another circle was this great now I'm hungry Thanks so this Lisa juice pattern is actually the result of this pendulum having two different periods now what would be the result if we ended up changing the lengths of these two strengths in this setup the upper string is much shooter and the lower string is much longer now let's see what it gives us once again we're gonna speed up the video otherwise this pattern would take about three and a half minutes in this case by shortening that pink string at the top I've made the two periods for this pendulum closer to each other you that's very pretty now let's change the lights again in this case the strings are tied together about half the entire distance I've sped up the video about one and a half times just to move it along a little bit quicker [Music] [Music] now let's try making the upper string even longer in this child the lower string is only about 1/4 the entire length this video is also about one and a half times faster let's try again now if this set up we got pretty close to a 2:1 ratio between the periods which means the pencil bob was moving twice as fast in this direction as it was in this direction and if we look very closely at the picture it kind of looks like a figure eight if we match that to the chart a two-to-one ratio as we can see gives us a figure eight so now that we see how we can record Lisa's use patterns with San in the next episode we're going to see how we can do it with light and also with paint [Music]

Channel: Bruce Yeany

Views: 8,526,772

Rating: 4.8206525 out of 5

Keywords: pendulum, sand pendulum, periodic motion, harmonic motion, Lissajous patterns

Id: uPbzhxYTioM

Length: 9min 52sec (592 seconds)

Published: Tue Mar 28 2017

Reddit Comments

[u/azmanam]

*pendulum

Looks even cooler if you speed the video up to 2x

[u/hillgaf]

Love this