Definition of Tension Force
In general, tension refers to the force transmitted when a cable, rope, wire, or string is tethered by forces acting on opposite ends. The cable is directed in one direction along its length and pulls equally on objects on either end of the cable.
The term tension may also be used to describe the action-reaction forces affecting each end of the two elements. In other words, tension is the opposite of compression.
Physical objects are forced to exert some force upon each other when they are in contact. In accordance with the kind of object, each of these contact forces will be assigned a unique name. Cables, chains, or ropes exert tension on objects when they are being pulled.
It is possible to transfer force - over a specified distance with ropes and cables, since they are efficient at transferring force. Pulling force originates from tension since ropes cannot push effectively. When a rope is pushed, it will become slack and lose tension, thus it will no longer be able to pull in its original position.
The Formula of Tension
The tension is equal to the mass of the object × gravitational acceleration for suspended objects which are in equilibrium.
T= mg
T= tension, N, kg-m/s2
m= mass, kg
g= gravitational force,
Newton's Laws and Tension Force
Newton's law is applied to tension in the final application. Cables and rope are usually used to transmit force, which causes tension. For example, let's consider a rope pulling a block. People pulling at one end of the rope cannot exert direct force on the block at the other end as they are not in contact with the block. So the rope exerts a force on the block which is transmitted to the block by the rope. An object experiencing tension force is a block.
Massless ropes or cables are the basis of classical mechanics. A massless cable or rope transmits force equally from one end to the other. By using the massless rope as an example, a person pulling a massless rope with the force 30 N then the pull experienced by the block will be the same 30 N.
The total force on a massless rope should always be zero. This can be proven using Newton’s second law. The mass of a massless rope equals the force acting upon it, so a net force on a rope causes infinite acceleration A=F/m and zero mass.
It is physically impossible to experience the net force in the situation described above, so the massless rope cannot experience it.
Consequently, all of the massless ropes will undergo equal and opposite tension forces. When a man pulls a block with a rope, the rope experiences tension from the pull in one direction, and tension from the reactive force of the block in the opposite direction.
The Tension in One Dimension
In one dimension string, the tension is a scalar quantity. The tension is not negative. When the tension is zero, the string is loose. Unlike ropes and strings, which have a dimension of length yet no cross-section, ropes and strings are massless. Since the tension is constant along the string, there will be no bends not caused by vibrations and pulleys, as they occur with vibrations and pulleys.
According to Newton's third law, these are the forces applied on the ends of the string or rope by the objects to which the ends are attached. When a string vibrates, the frequencies it produces are determined by its tension. These frequencies are derived from Newton's law of motion.
Three Dimensions of Tension
In addition, tension is also used to describe a force that is generated by the ends of three-dimensional continuous material, such as truss and rods. Such rods swell under tension.
Stress=axial force/cross-sectional area
So failure is caused by both the lengthening and the load, as both are determined by the force per cross-sectional area rather than the force alone. Stress is a 3×3 matrix. It is called a tensor.
FAQs on Tension Force
1. What is meant by tension force in Physics?
Tension force is the pulling force transmitted axially through a string, rope, cable, or similar object when it is pulled tight by forces acting from opposite ends. The force is directed along the length of the object and pulls equally on the objects connected at either end.
2. What is the formula for tension and what is its SI unit?
The formula for tension depends on the situation. For a simple case where an object of mass 'm' is hanging in equilibrium (not accelerating), the tension (T) in the string equals the gravitational force, so T = mg. The SI unit for tension, like any other force, is the Newton (N).
3. What are some real-world examples of tension force?
Tension force is present in many everyday situations. Some common examples include:
- The force in a rope during a game of tug-of-war.
- The force in the cable holding an elevator.
- The force on a guitar string when it is tuned.
- The force in the chain of a swing supporting a person.
- The force in the wire holding a picture frame against a wall.
4. How does the tension in a string change if a suspended object is accelerating?
When a suspended object accelerates, the tension is no longer equal to its weight. If the object is accelerating upwards with acceleration 'a', the tension is T = m(g + a). If it is accelerating downwards with acceleration 'a', the tension is T = m(g - a). Here, 'm' is the mass and 'g' is the acceleration due to gravity.
5. How does tension force relate to Newton's Third Law of Motion?
Tension perfectly illustrates Newton's Third Law. If a rope pulls on a block with a certain tension force, the block simultaneously pulls back on the rope with an equal and opposite force. These two forces form an action-reaction pair, defining the tension within the rope.
6. What is the key difference between tension and compression?
The primary difference lies in the direction of the force relative to the object. Tension is a pulling force that tends to stretch or elongate an object, like pulling on a rope. In contrast, compression is a pushing force that squeezes or shortens an object, like squeezing a spring. Ropes and strings are designed to withstand tension but buckle under compression.
7. Why do we often assume strings are 'massless' in Physics problems involving tension?
Assuming a string is massless is a crucial simplification. According to Newton's Second Law (F=ma), if a string had mass, different segments would require a net force to accelerate. This would mean the tension would vary along the string. By assuming the mass is zero, any net force would cause infinite acceleration, which is physically impossible. Therefore, the net force on any part of a massless string must be zero, which implies the tension is constant throughout its entire length.
8. Can tension force have a negative value?
No, tension is defined as a pulling force and is always considered a non-negative quantity. A tension of zero indicates the string is slack or loose. A negative tension would conceptually imply a 'pushing' force, which strings and ropes cannot exert; this is the domain of compression. Therefore, tension is always positive when a string is taut.
