This is a very simple yet powerful demonstration that shows how potential energy and kinetic energy transfer from one to the other and back again, over and over. Once you wrap your head around this concept, you'll be well on your way to designing world-class roller coasters.
For these experiments, find your materials:
- some string
- a bit of tape
- a washer or a weight of some kind
- set of magnets (at least 6, but more is better)
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Here's what you do:
1. Make the string into a 2 foot or so length.
2. Tie the string to the washer, or weight.
3. Tape the other end of the string to a table.
4. Lift the weight and let go, causing the weight to swing back and forth at the end of the pendulum.
Download Student Worksheet & Exercises
Watch the pendulum for a bit and describe what it’s doing as far as energy goes. Some questions to think about include:
- Where is the potential energy greatest?
- Where is the kinetic energy greatest?
- Where is potential energy lowest?
- Where is kinetic energy lowest?
- Where is KE increasing, and PE is decreasing?
- Where is PE increasing and KE decreasing?
- Where did the energy come from in the first place?
Remember, potential energy is highest where the weight is the highest.
Kinetic energy is highest were the weight is moving the fastest. So potential energy is highest at the ends of the swings. Here’s a coincidence, that’s also where kinetic energy is the lowest since the weight is moving the least.
Where’s potential energy the lowest? At the middle or lowest part of the swing. Another coincidence, this is where kinetic energy is the highest! Now, wait a minute...coincidence or physics? It’s physics right?
In fact, it’s conservation of energy. No energy is created or destroyed, so as PE gets lower KE must get higher. As KE gets higher PE must get lower. It’s the law...the law of conservation of energy! Lastly, where did the energy come from in the first place? It came from you. You added energy (increased PE) when you lifted the weight.
(By the way, you did work on the weight by lifting it the distance you lifted it. You put a certain amount of Joules of energy into the pendulum system. Where did you get that energy? From your morning Wheaties!)
Chaos Pendulum
For this next experiment, we'll be using magnets to add energy into the system by having a magnetic pendulum interact with magnets carefully spaced around the pendulum. Watch the video to learn how to set this one up. You'll need a set of magnets (at least one of them is a ring magnet so you can easily thread a string through it), tape, string, and a table or chair. Are you ready?
Exercises
- Why can we never make a machine that powers itself over and over again?
- Energy is mostly lost to heat.
- Energy is completely used up.
- Energy is unlimited, but is absorbed by neighboring air molecules.
- None of these
- In the pendulum, as kinetic energy increases, potential energy ______________.
- Increases
- Decreases
- As potential energy decreases, kinetic energy _________________.
- Increases
- Decreases
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I can here it fine! the pendulum is kind of ok.
Of course! Use anything for a weight that you have handy, like a rock.
can you use something other than a nut
🙂
Yes! That’s how generators work! They move magnets past a coil of wire, which causes a current to flow in the wire and can be used for all sorts of things! Great idea!
You can make the motor generator project in Unit 11.
We made the chaos pendulum and it is really cool. We were wondering if a machine based on this design (magnets and pendulum) could be used to generate electrical power. If not, why not?
The pendulum hits the molecules in the air (mostly oxygen and nitrogen) which low down the pendulum. In space it would go forever since there aren’t many molecules to hit.
how does the air take away the power of the pendulim
Centripetal (translation = “center-seeking” ) is the force needed to keep an object following a curved path. Objects will travel in a straight line unless they bump into something or have another force acting on it (gravity, drag force, etc.). If you swing a bucket around in a circle, you have to exert a pull on the handle to keep the bucket going around in a circle. If you let go, the bucket flies off in a straight line (initially) and then it moves under the influence of gravity and hits the ground. WHAM! Does that help?
What about centripical force?
Yes, a pendulum swing would swing forever in a vacuum (no air resistance) if it also had a frictionless bearing (no energy lost due to friction) assuming that it’s on Earth, and no other forces other than gravity act on the pendulum. A pendulum swings back and forth because of gravity. If you’re far enough in space away from the influence of other objects like stars or planets or black holes, then your pendulum won’t swing – it will move in a straight line.
I mean swinged
If you swigged one of this in space would It go forever?
The sound is working over here – what happens if you try a different computer?
WHAT ABOUT speaking louder???
oops-do you have any other suggestions?
NOW thanks!
We turned both speakers on but it still didn’t work
thanks,Anne Agah
The chaos pendulum is wonderful. The kids have been experimenting with it all afternoon. I’m waiting for them to finish so i can play with it. 🙂
thanks
This video was recorded in mono by accident (don’t ask) – just turn up the volume on both speakers and you should be able to hear it fine. We’re working to fix this problem! 🙂
I cain’t get any sound for the chaus pendulum video what do i do
Have you ever seen Astro Jax?
http://www.activepeople.com/en/toys/astrojax/
kinda reminds me of a double pendulum.
When you wrapped the string around the pen, you made a simple machine!
Holly Thomson 12
Oops – sorry about that.. all fixed now.
The second video for “Chaos Pendulum” appears to not be available. Can you fix it?
Thanks.