Question

What's the formula for tension?

Answer 1

tension depends on the physical situation...

Answer 2

there really is no equation for tension, as its just another force, and the cardinal equation for forces is
Σ
F=ma (or in this case, F with a t subscript for tension). I suppose your equation Tension=weight +/-mass*acceleration is correct, but again, there is no formal equation for tension. The most important thing above all else, and this can never be stressed enough, is to draw a freebody diagram to see how each force is acting on each body.

Now suppose you had a system where a rope is pulling up a block of mass m with force Ft, and acceleration (a). Heres how i would write out my work if this were a test:
1)
Σ
F=ma
2)Then specify each force: Ft-Fg=ma
3)move around: Ft=ma+Fg (or you can make in mg at this point)
4)Simplify:Ft=m(a+g)

Now of course, this problem gets more annoying if it involves an atwood machine, or a machine that has two masses connected by a rope over a pulley. the problem becomes an even bigger pain when the pulley is given a moment of inertia, but you can save that for later

Answer 3

han_nah's my classmate and i dont quite understand the question..