In this experiment you will be adjusting the length of string of a pendulum until you get a pendulum that has a frequency of .5 Hz, 1 Hz and 2 Hz. Remember, a Hz is one vibration (or in this case swing) per second. So .5 Hz would be half a swing per second (swing one way but not back to the start). 1 Hz would be one full swing per second. Lastly, 2 Hz would be two swings per second. A swing is the same as a vibration so the pendulum must move away from where you dropped it and then swing back to where it began for it to be one full swing/vibration.
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You’ll need:
- 3 Foot Long String
- A Weight that can be tied to the end of the string
- A Timer or Stopwatch
- Masking Tape
- A Table or Chair
- A Partner is helpful
“Advanced students: Download your What is Frequency?”
1. Tie your weight (the official name of the weight on the end is bob. Personally I’ve always preferred the name Shirley, but Bob it is.) to the end of the 3 foot string. If you’ve done the gravity lesson in the Mechanics set of lessons you’ll remember that the weight of the bob doesn’t matter. Gravity accelerates all things equally, so your pendulum will swing at the same speed no matter what the weight of the bob.
2. Tape the string to a table or chair or door jam. Make sure it can swing freely at about 3 feet of length.
3. I would recommend starting with 1 Hz. It tends to be the easiest to find. Then try .5 Hz and then 2 Hz.
4. The easiest way I’ve found to do this is to start the pendulum swinging and at the same time start the timer. Count how many swings you get in ten seconds.
5. Now, adjust the string. Make it longer or shorter and try again. When you get 10 swings in 10 seconds you got it! That’s one swing per second. You should be able to get quite close to one swing per second which is 1 Hz.
6. Now try to get .5 Hz. In this case you will get 5 swings in ten seconds when you find it. (A little hint, the string is pretty long here.)
7. Now speed things up a bit and see if you can get 2 Hz. Be prepared to count quick. That’s 2 swings a second or 20 swings in 10 seconds! (Another little hint, the string is quite short for this one.)
Did you get all three different frequency pendulums? It takes a while but my classes found it rather fun. You’ve created three different frequencies. 2 Hz being the fastest frequency. That was pretty fast right? Can you imagine something going at 10 Hz? 100 Hz? 1,000,000 Hz? I told you things were moving at outrageous speeds!
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Good question! You would treat it as two different problems, each with it’s own pendulum string length.
If something interferes with the string while the pendulum is swinging–but only on one side of its vibration path–and in effect shortens the string when it’s going one direction in the vibration, how is the whole thing measured?
So me an my boys and my daughter took rope and a put a loop in one end using a square knot and we hung my tape measure at one end and looped the rope around the top of our swing set one time. So we played around with the length of the rope and we got pretty darn close to 1 Hz at 4.99 seconds for five cycles. We then found the length for 0.5 Hz, but when we went for 2 Hz the rope was so short my tape measure was hitting the top of the swing set. 😛 It was a lot of fun and it opened up the door to talk about sound waves and what the different rates in Hz mean.
Try water first, since it’s a lot easier to see with smaller particles that can move easily among each other. Topsoil will need a larger driver, which means a bigger amp and lower frequency waves, which is difficult to come by for most folks. Did you see the demo in this section where you could actually see the speaker move in and out about once per second? Look in the experiments list near the bottom – I think it’s the last one.
I’d love to see a demonstration of the Hz moving sand. I tried with some top soil that was is a bucket and had no movement.
TINNITUS, or ringing ears, has a number of possible causes. Apparently many people suffer from this condition. Here are the possible causes if it troubles you more than just once in awhile:
– damage to the ear drum, which includes being exposed to loud noise (such as a gunshot) or continuous exposure to loud noise (listening to loud music a lot)
– sinus congestion: when the sinuses are congested, they are under pressure which affect the ears.
– hearing loss: as your hearing decreases, the inner ear hair cells get weaker, sending a signal to the brain. In quiet conditions this signal is heard as ringing.
– drug interaction, as many drugs have chemicals that interact with our bodies in negative ways, many affecting the nervous system, which includes our inner ear.
You know, I have often wondered that, too! I will look into it and get back to you when I hear more (sorry for the pun!)
Aurora,
Why do we get a very high pitch ringing in our ears?
Lori
Sometimes it just takes the right amount of jiggling force – but you can certainly try a longer string and see how it goes.
our three foot string was not long enough to get to half a hz… almost, but not quite- did we do it wrong or should we have started with a longer string?
You’re so welcome! Keep it handy for the next TWO teleclasses..
Aurora, I can’t thank you enough for the great prize I just recieved in the mail! It is awesome. THANK YOU SO MUCH!
For some reason we couldn’t make the frequency be 1 second, but the closest we got was 1.15 sec.
sevy keble 🙂