How Do I Calculate Tension Force?

Written by mike goldstein
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How Do I Calculate Tension Force?
The tension on a cord can be found using Newton's Second Law. (crane pulley image by Stephen Orsillo from

Assume an object is suspended from a beam via a string. The string experiences a force of magnitude, T, both from the beam and the object. Newton's Third Law states that both forces should be equal and in opposite directions. This force is called the tension force.

Newton's Second Law

Using the example of a single object being suspended by a single string from a beam, we can apply Newton's Second Law to find the tension force. Newton's Second Law states that force equals mass multiplied by acceleration, or F = ma. In our case, the acceleration is equal to the force of gravity, g. So, if we plug in our values, T = mg.

Newton's Third Law

Newton's Third Law states that the string has two forces acting on it of equal magnitude and opposite direction. The total tension force should equal zero. Thus, we get T - mg = 0, and we can solve for T to get the tension force.

Horizontal Components

For strings with horizontal components, divide the vector and find the tension for the horizontal and vertical components separately. For the horizontal component, find the cosine of the angle away from horizontal. For example, a string 60 degrees from horizontal would have a horizontal component of Tcos(60) = T/2. For the vertical component, do the same thing with the sine of the angle.

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