Tension - Definition, Examples, Units, Formula, FAQs
Tension Force is an important concept in Physics, especially in the chapter Laws of Motion for Class 11. It is a contact force transmitted through a string, rope, wire, or cable when it is pulled tight by forces acting at opposite ends. Tension always acts as a pulling force and works along the length of the string, away from the object. Understanding tension is essential for solving problems related to hanging bodies, pulleys, elevators, and connected systems. The basic formula in equilibrium is T = mg, where tension balances the weight of the object. This concept is frequently asked in board exams as well as competitive exams like JEE and NEET. In this article, learn the definition, formula, units, direction, examples, and common misconceptions about tension force.
What is Tension Force?
Tension in physics is a contact force. The tightness of a rope or string when you try to stretch it is called tension.
Tension is the force transmitted through a string, rope, wire, or cable when it is pulled tight by forces acting from opposite ends. It is a pulling force that acts along the length of the object and always acts away from the body to which it is applied.
Tension Force -Example
A stone is suspended with the help of a thread and its free end is fastened to the ceiling, as shown in Figure
Gravity pushes a stone attached to a string down all the time, but the stone does not fall since it is held by the string. As a result, there is a force that pulls the stone upward to support it against gravity.
(Image drawn using Microsoft paint)
The upward tension force balances the gravitational force in the case above, as seen in the diagram below.
(Image drawn using Microsoft word)
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Common Misconception About Tension
A very common misconception is that tension can act as both a pulling and pushing force. In reality, tension is only a pulling force. Ropes, strings, and cables cannot push effectively. If you try to push a rope, it simply becomes loose or slack and loses its tension.
This confusion often appears while drawing free-body diagrams. Students sometimes show the tension force acting toward the object as if it is pushing it. However, tension always acts away from the object, along the length of the rope or string.
Units of Tension
- SI Unit: Newton (N)
- CGS Unit: Dyne
- Dimensional Formula: $\left[M L T^{-2}\right]$
Since tension is a force, it has the same units and dimensions as force.
Tension Force Formula
When an object is hanging at rest or moving with constant velocity, the system is in equilibrium (acceleration $=0$ ). In this case, the upward tension ( $\mathbf{T}$ ) in the string or cable is equal to the downward weight (mg) of the object.
$
T=m g
$
Where:
$\mathbf{T}=$ Tension (in newtons, N)
$\mathbf{m}=$ Mass of the object (in kilograms, kg)
$\mathbf{g}=$ Acceleration due to gravity $\left(9.8 \mathrm{~m} / \mathrm{s}^2\right)$
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Direction of Tension Force
This "pull" is a force we refer to as tension. As a result, tension will point away from the mass and toward the string. The string, in the instance of the hanging mass, pulls it up, exerting an upward force on mass, along with tension upwards..
Also Read:
- NCERT solutions for Class 11 Physics Chapter 5 Laws of Motion
- NCERT Exemplar Class 11 Physics Solutions Chapter 5 Laws of Motion
- NCERT notes Class 11 Physics Chapter 5 Laws of Motion
Why is the Tension of a Massless String Constant?
Because a string is extended and non-rigid, tension exists throughout the thread rather than being applied at a single location, the concept of tension in a string might be difficult to grasp.
What is the Importance of Tension Force?
All physical things that come into contact with one another can exert forces on one another. It's vital to remember that tension is a pulling force because ropes can't effectively push. When you try to pull anything with a rope, it becomes slack and loses the tension that allowed it to pull in the first place.
Also check-
- NCERT Exemplar Class 11th Physics Solutions
- NCERT Exemplar Class 12th Physics Solutions
- NCERT Exemplar Solutions for All Subjects
NCERT Physics Notes:
Frequently Asked Questions (FAQs)
The pull, which is called tension, is the direction of tension. A thread pulls the mass upwards in the case of a hanging mass, hence the string/rope exerts an upper force on the mass and the tension is on the upper side.
The string has a tensile force of 10 N.
The gravitational force acts in the opposite direction of tension. If an object is suspended, tension must be used to keep it balanced; otherwise, gravity will cause it to fall.
Because the rope works as a force transfer agent, there should never be a situation when two items connected by one rope are subjected to tension forces of different magnitudes.
The amount of work done is determined by both force and displacement. Although tension is a force, it does not result in any displacement. In the case of tension, W = F 0 = 0 if the work done is given by the equation W = FS where F is the force and S is the displacement. As a result, tension produces little work.
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