Tension in string when force is applied to both ends

[vaizard]

Hi,

I've got a quick question about tension. If there is a force applied to both ends, the total tension is the sum of those forces, right (i.e., they don't cancel each other out)?

TIA!

[Doc Al]

Wrong. Take a massless string for example. To create a tension of 100 N within the string, you must apply a force of 100 N to both ends. (Those forces don't add up.)

[vaizard]

So when the string is vertical and in equilibrium with a mass hanging from it, there is a certain force exerted downwards by the mass and that same force exerted upwards by whatever the top end of the string is attached to?

[Doc Al]

That's right.