# String Tension?

1. Nov 25, 2006

### Aladin

Please explain the direction of tension in a string .

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2. Nov 26, 2006

### Aladin

please repply me as soon as possible

3. Nov 27, 2006

### Integral

Staff Emeritus
What is your coordinate system? Where is your origin, which direction is positive and which direction is negative?

4. Nov 27, 2006

### TheloniousMONK

Recall that at any point on a string under tension, there will be a force acting up and another force acting down the string. Furthermore, recall that these forces must be equal.

5. Nov 27, 2006

### Staff: Mentor

acceleration constraint

I suspect that you understand perfectly well that the string tension pulls up on both masses. What you are trying to understand is how the signs are chosen in the equations.

What you need to understand is the how the acceleration of m_1 relates to the acceleration of m_2. Since they are connected by a cord, they are constrained to move together. If you arbitrarily call the acceleration of m_1 to be "a" upward, what must be the acceleration of m_2?

Once you understand the above "acceleration constraint", you can pick a coordinate system and write your equations. For example, choose up to be + and down to be -. Use that convention and try writing the equations for each mass.

6. Nov 27, 2006

### TheloniousMONK

Right. And if all else fails, split your system into parts and draw your FDB with your axes included.

7. Nov 27, 2006

### Aladin

I am not understand please just tell me about the sign that are used in both equations.

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