# Tension in strings

1. Nov 1, 2012

### sambarbarian

I am trying to self learn kinematics , but i don't understand a certain concept :-

If a string hold a mass which in turn holds another mass by a string.

by F.B.D to in forming the first equation , we take T1 = m1g +t2

but shouldn't the second mass be included as well.

eg. if we are hanging something with a thread and someone hangs another string and mass to it , the strain on the first string is increases .

I am sorry for the vague outline i could give , hope you can understand it .

2. Nov 1, 2012

### arildno

Wouldn't that be included in the expression for T2?

T1 is the force needed to keep mass1 in equilibrium.
The forces actually "attacking" mass1 are the two tensions and its own weight.

T1 must be equal to, and oppositely directed to the sum of the two other forces attacking mass1.
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Thus, when you do this problem, always keep in mind that we are tracking the forces attacking some material OBJECT, and we set up our equations for each object SEPARATELY.

Thus, you will ALSO have the equation:
T2=m2g, in order to keep mass2 in equilibrium.