Video Transcript
Which of the following is the term used to refer to the energy that a solid object has if it is elastically deformed? (A) Internal energy, (B) mechanical energy, (C) kinetic energy, (D) elastic potential energy.
We can start out by considering what it means for a solid object to be elastically deformed. Say that this here is our solid object. We know that if this object is deformed, that means its shape has changed. Say, for example, that we press down on the top and bottom of our object so that it’s flattened out. By changing this object’s shape, we’ve deformed it. But what if we then stop pressing on the top and bottom of our object, and as a result, it goes back to its original shape?
If that happens, then we would say that this deformation is elastic. In other words, we’ve changed the shape of this object that has a tendency to return to that shape. That’s elastic deformation. And we want to figure out which of these four terms relates to the energy associated with this deformation. Let’s begin by coming to an understanding of what these different terms mean, starting with the first term internal energy. Internal energy describes the energy of particles that make up an object. For example, if we had a gas sealed in a container, then the internal energy of this gas would be equal to the sum of the energy of each of the gas particles. That’s what this term internal energy refers to.
Thinking about our solid object that’s been elastically deformed, we know that the energy this object acquires when its shape is changed doesn’t have to do with particle motion inside the object. Rather, it has to do with the object’s overall structure. So, for that reason, we’ll cross off option (A). Internal energy is not the best term to refer to the energy of an object that’s been elastically deformed.
Moving on to option (B), mechanical energy, the mechanical energy of an object is equal to the sum of its kinetic and potential energies. So, for example, if we had a projectile flying through the air, then it would have some amount of kinetic energy thanks to its speed and mass. And it would also have some gravitational potential energy, depending on its height above Earth’s surface. Our elastically deformed object though doesn’t have anything to do with kinetic energy, energy of motion. So this term also isn’t the one that we’ll pick as our answer.
Considering option (C), which is kinetic energy, we’ve already seen that it’s not through motion of the body overall that our elastically deformed object gains energy. So kinetic energy will not be the term we choose.
This brings us, finally, to elastic potential energy. This describes the potential energy or stored energy in an object when that object’s shape has been changed. For example, this is the energy that’s stored in a spring when it’s stretched out. When the spring is stretched, it tries to return to its natural length. To do so, it expends what is called elastic potential energy.
Considering our deformed solid object, we can see that this is the same type of energy present here. It’s the energy present in our object at this point that tends to make it return to its original shape. This energy is latent in the object and therefore it’s potential energy. And it’s also associated with the object returning to its original form, and therefore it’s elastic.
So then elastic potential energy, option (D), is our choice. This is the term used to refer to the energy of a solid object that is elastically deformed.
