Use a free-body diagram of the object attached to the string
Apply Newton’s second law, ( sum F = ma )
For an object at rest or moving at constant velocity, set acceleration to zero
Solve for the string force from the balance of forces
For a hanging mass at rest, tension equals the weight: ( T = mg )
For an accelerating hanging mass, use ( T – mg = ma ) or ( mg – T = ma ), depending on direction
For a mass on a horizontal surface pulled by a string, use the horizontal force equation
For a mass in circular motion, use the centripetal force relation: ( T = frac{mv^2}{r} ) when tension provides the centripetal force
For an angled string, resolve tension into components using trigonometry
If there are multiple masses or pulleys, write one equation for each object and solve the system together
Include friction, if present, in the force balance
Check units to ensure the result is in newtons (N)