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Physics Lesson 4.4.4 - What is Tension?
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Welcome to our Physics lesson on What is Tension?, this is the fourth lesson of our suite of physics lessons covering the topic of Types of Forces III (Elastic Force and Tension), you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
What is Tension?
Tension is another resistive force that appears when a string is pulling a load. In other words, tension is the resistive force of a string against deformation caused when it is pulling an object. It is obvious that tension is in the opposite direction of the pulling force as shown in the figures below.
In the first case (figure a) the tension acts against the gravity, while in the second case (figure b), it acts against friction. Tension has an intermolecular nature, i.e. it appears when the molecules of the string (which is a solid and as such, its molecules have a strong connection between them) display resistance towards extension.
Tension is different from elastic force, as it appears when the string is non-elastic. Therefore, no visible extension appears in the string, but even in cases when this extension is noticeable, the string does not turn back to its original length, and as a result, it is considered as a non-elastic material. Therefore, the Hooke's Law cannot be used to calculate the value of tension.
Example 3
What is the minimum tension present in a rope if it is used to lift a 30 kg object? Take g⃗ = 9.81 m/s2.
Solution 3
The situation is described in the figure below.
The minimum tension occurs when its value is equal to that of the gravitational force. Thus, we have
T⃗min = -F⃗g
= -m × g⃗
= -30kg × 9.81N/kg
= -294.3N
The sign minus means that the tension acts in the opposite direction of gravity.
You have reached the end of Physics lesson 4.4.4 What is Tension?. There are 4 lessons in this physics tutorial covering Types of Forces III (Elastic Force and Tension), you can access all the lessons from this tutorial below.
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