Strain Energy: Definition & Calculation

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  • 0:04 Strain Energy
  • 1:03 Stress and Strain
  • 1:56 Calculating Strain Energy
  • 2:58 Example Calculation
  • 3:27 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Whenever you push or pull on a deformable object like a rubber band or spring, you transfer some energy to it. This is known as strain energy. Learn how to calculate it in this lesson!

Strain Energy

Lauren is having a great time jumping on her trampoline. Every time she comes down and hits the trampoline, the springs attached to the sides stretch out, causing her to slow down and stop for just a moment. Then, the springs start to contract again, throwing Lauren back up into the air!

What's really going on here? To understand it, you first need to know something about energy. When Lauren is falling down toward the trampoline, she has a lot of kinetic energy, which is the energy that an object has due to its motion. Then, when she hits the trampoline, the springs begin to stretch, and as they stretch more and more, Lauren's kinetic energy is transferred into the springs until she comes to a stop.

When a deformable structure, like a spring, stretches, it stores a type of energy known as strain energy. In many cases, this energy can be turned back into kinetic energy relatively easily. That's certainly true for the trampoline. As the springs return to their original length, their strain energy is transferred back to Lauren in the form of kinetic energy, and she flies up into the air.

Stress and Strain

Whenever a force is applied to an object of a deformable material, it will change its shape. Sometimes, this is a big change, such as when you stretch out a rubber band. Other times, it's hard to see, like when a load is applied to a steel support beam. We can quantity exactly how much an object changes shape by measuring something called strain, which is the change in length of the object divided by its original length.

As more and more force is applied, the object will continue to stretch. Stress is the amount of force applied divided by the cross-sectional area of the object.

Stress measures the amount of force applied to an object, while strain measures how much it stretches.
Stress and strain

The ratio of stress to strain is known as Young's modulus, or E, where:

Youngs modulus

Young's modulus is an important material property that tells you how stiff a material is. Something that's very stretchy, like a rubber band, will have a small Young's modulus, while something that is very stiff, like steel, will have a really large Young's modulus.

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