Main Difference – Tension vs. Compression
Tension and compression refer to forces that attempt to deform an object. The main difference between tension and compression is that tension refers to forces that attempt to elongate a body, whereas compression refers to forces that attempt to shorten the body.
What is Tension
Tension refers to forces that attempt to elongate a body. Whenever you hang an object from a string, for example, the object’s weight pulls on the string, attempting to elongate it. We call the force that is trying to stretch the string “tension”. Due to tension, the molecules that make up the string are forced to move away from their equilibrium positions. The molecules attempt to move back towards their equilibrium position, and in doing so they pull back on the objects that attempt to elongate them. If the forces balance out, then the system comes to an equilibrium, although the string is still under tension and may be elongated beyond its original length.
The tension per unit area (the area referred to here is the cross-sectional area, which is at right angles to the force) is often referred to as tensile stress. The term tensile strain refers to the increase in length divided by the original length of the body.
What is Compression
Compression refers to forces that attempt to shorten an object. For example, if you push down on a spring you are exerting a compressive force on it. If compressive forces act along one direction, the compression is called uniaxial. If the compressive forces act along two or three directions, they are termed biaxial and triaxial compression respectively.
The compressive force per unit area (once again, we refer to the cross-sectional area here) of the object is called compressive stress. The ratio of the reduction in length divided by the original length is referred to as the compressive strain.
When objects bend, they are under compression and tension at the same time. For instance, consider the I-beam shown below:
The top of the beam is under compression while the bottom of the beam is under tension. The line running along the centre of the beam is not under tension or compression. The top and bottom of the I-beam are made thicker (giving it the “I” shape) because these are the regions that experience the most force. Since stress is the force per unit area, having a large surface area allows for the stress on the ends of the beam to be reduced.
Difference Between Tension and Compression
Effects of Force
Tension is a force that attempts to elongate an object.
Compression is a force that attempts to shorten an object.
“Tug of War!” by Jason Eppink (Own work) [CC BY 2.0], via flickr
“Benging an I-beam” by Avenafatua (Own work) [Public Domain], via Wikimedia Commons