TENSION: how do you calculate it?

[hebden]

is there any specific formula or formulas for calculating tension? is T=ma legit?

[robphy]

Generally, in introductory physics, the tension is not determined by a general formula. If one needs to determine it, it is often an unknown force contributing to the net-force on an object, which appears on one side of Newton's Second Law. So... no, T=ma is not generally "legit".