Elastic and plastic behaviour

Introduction to Elasticity

Have you ever noticed how a rubber band goes back to its normal size after you stretch it? Or how a slinky spring bounces back when you let it go? This ability of a material to return to its original shape is a very important branch of Physics called Elasticity.

However, not all materials behave this way. If you take a piece of wet garri or fufu and pull it, it stays pulled. It does not snap back like a spring. This difference is what we call elastic and plastic behavior.

Elastic behaviour

Elasticity is the ability of a material to regain its original shape and size after the force pulling it has been removed. Imagine pulling a door spring; once you let go, it snaps back to the exact length it was before. This is because the molecules inside are like tiny magnets trying to stay in their original positions.

In simple terms, elasticity is the 'snap-back' power of a material.

Plastic behaviour

Plasticity is the opposite of elasticity. If you apply force to a material and it changes shape permanently, it is being plastic. A good example is plasticine or moist clay used in pottery. If you squeeze it, it stays squeezed. It does not try to go back to how it was.

Basically, plasticity means the material has 'given up' and decided to stay in its new shape.

The Elastic Limit

Every material has a breaking point or a limit. If you take your mother's hair bond and pull it too hard, it might not snap back anymore. It becomes thin and weak. We say you have exceeded the Elastic Limit.

If you pass this limit, the material will never be the same again.

Differences between Elastic and Plastic materials:

Elastic materials store energy when stretched, while plastic materials do not.

Elastic materials return to original size; plastic materials show permanent change.

Steel and rubber are elastic; lead, clay, and plasticine are plastic.

Practical example of Elasticity

Think of the shock absorbers in a Danfo bus or a car. They are big springs that show elastic behavior. When the bus hits a pothole, the spring compresses (gets shorter) to absorb the shock and then returns to its original height so the passengers don't keep bouncing forever.

If the spring was plastic, the bus would stay low to the ground after the first pothole, and the chassis would eventually scrape the road.