We assume that the strings used in the different systems have a very small mass and may be neglected. Tension forces in the different strings are analysed. įor a massless string or cord, the tension is the same everywhere.Įxamples with Detailed Solutions In all the examples below are theįree body diagram for several systems with strings and pulleys. |T ' 1 | = |T ' 2 | which is mostly needed to solve problems involving strings, cords. T 2 and T ' 2 are also action-reaction pair and are also equal in magnitude and opposite side. T 1 and T ' 1 are action-reaction pair and are therefore equal in magnitude and opposite side. The direction of the tension may or may not be the same. Note the tension has the same magnitude everywhere for a massless string (and frictionless pulley if used). Now since |T 1 | and |T 2 | are equal for massless strings, the effect of the string is to transmit forces between distant points through the tension in the string. If the weight of the string w ' is very small compared to |T 2 | and |T 1 |, it can be neglected and we end up with The string is also at rest, hence by Newton's second law, we have Using the same system of axes described above, we express T 1, w ' and T 2 in components form using magnitude and direction as follows T ' 1 and W have equal magnitude and opposite direction which explains why the box is at rest.Ģ) The forces acting on the string are the force T 1 exerted by the box on the string as a reaction to T ' 1, T 2 exerted by the ceiling on the string and w ' the weight of the string. Since the box is at rest, from Newton's second law, we have Let x-y be a rectangular coordinate system and express W and T ' 1 by their components using magnitude and direction as follows: Consider the system of a box that hangs at rest from a ceiling as shown below.įree body diagram of the box, the forces acting on the box are: the weight of the box W and T ' 1 the force exerted by the string on the box. What is the tension of a string? The concept of tension of strings is used to explain the transmission of forces from one point to another.

Falling blocks on a string physics