# Homework Help: What does the period of a normal pendulum depend on?

1. Jan 9, 2014

### Dumbledore211

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

If a simple pendulum has a metal bob having negative charge and is allowed to oscillate above a positively charged metallic plate will the time period increase, decrease, become zero or remain the same. Could you guys please give me an insight into what happens in the situation

2. Relevant equations

3. The attempt at a solution

2. Jan 9, 2014

### Pythagorean

What does the period of a normal pendulum depend on?

3. Jan 9, 2014

### Dumbledore211

It depends basically on the length of the thread or the string and the value of g of the particular place. Since the tension will increase in this situation, won't the length of the string expand leading to an increase in the value of time period???

Last edited: Jan 9, 2014
4. Jan 9, 2014

### Pythagorean

Well, that depends on whether you take the string to be rigid or not. Generally, at undergraduate level, if we consider a string that changes length, we explicitly say so. Otherwise, we assume a rigid string.

What can we replace g with here?

5. Jan 9, 2014

### Dumbledore211

We can assume g to be 9.8. So, assuming that the string does change length, is my conjecture correct to some extent???

6. Jan 9, 2014

### Dumbledore211

if the string is taken to be rigid then the time period will remain the same considering that everything remains unchanged.

7. Jan 9, 2014

### haruspex

What are the forces on the bob when the pendulum is displaced from the vertical? Do the usual free body diagram.