# Homework Help: Pendulum, very easy problem

1. Nov 28, 2007

### 4.19mile

1. The problem statement, all variables and given/known data

So basically, we had a mass attached to a string (like a pendulum), and we pulled it back .1 m and then let go and watched it go back and forth. We have a huge lab to do for stuff like this, and there were three questions that I want to be sure I get right since they lead to other questions:

1. How did the period of oscillation of the pendulum change as it swung back and forth over a long period of time?

2. How did the amplitude of the pendulum's motion change as it swung back and forth over a long period of time?

3. How does the amplitude of a period's motion affect its period of oscillation?
2. Relevant equations

None.

3. The attempt at a solution

So for #1, I'm not sure.. I thought initially it would increase over time, but I guess it would get "smaller and smaller" (the amount of oscillation), so would it decrease?

For #2, the amplitude would decrease, because of things like air resistance the distance the pendulum was going back and forth would get smaller and smaller till it finally came to a stop?

#3, the lower the amplitude, the lower the period?

This is what I think it is, but I really want to be sure as this leads to other questions. I'd appreciate it if someone could help. Thanks :)!

2. Nov 28, 2007

### G01

The amplitude will definitely decrease as time goes on, but think about the period for a little while.

Do you know of any formulas involving the period? Does the period of a pendulum depend on the amplitude of oscillation in those formulas? If not, what does this tell you about the period as the amplitude changes?

3. Nov 28, 2007

### stewartcs

4. Nov 28, 2007

### HallsofIvy

Isn't the point of a lab to SEE what happens? You shouldn't be thinking about what "would" or "should" happen. What DID happen in the lab?

5. Nov 28, 2007

### stewartcs

Knowing what should happen often helps to recognize what to look for and understand what is happening in the lab. It is not always easy to see a phenomenon and immediately conceive what it means. Let alone write it in scientific terms.

6. Nov 28, 2007

### 4.19mile

Thanks for all the help. Yes, the formula for the period doesn't have anything to do with the amplitude right (Since T = 2(pi) square root of L/g)? I am still a bit confused though.. I understand why the amplitude would decrease, but wouldn't a lower amplitude mean it takes less time to go back and forth, lowering the period?

7. Nov 28, 2007

### 4.19mile

I'd also appreciate it if anyone could confirm another thing:

Looking at pendulum mass vs. period, what does the trend seem like?
I think when the mass increases, the period increases as well.

8. Nov 29, 2007

### G01

Yes, the amplitude may be less, meaning the distance covered is less, but the pendulum also moves more slowly. Thus, the oscillations of lesser amplitude take the same amount of time.

Again, look at the relevant formulas. Does the mass of the pendulum bob appear in the formulas for the period? If, so, how does it affect the period?

Last edited: Nov 29, 2007