Hello, today we're going to talk about plastic and elastic deformation. Now defamation is a word that we're going to come across a few times in the next couple of videos. It's a long word but really it just means change in shape. Change in shape. So D's to not and form shape. So not the original shape. So when every force applies to an object then you've got a couple of things that can happen. If you've only got one force acting on the object so here's my helpful bit ball of play dough and if I only have one force applying to the object then that object will accelerate. It will get faster in one direction or another. On the other hand in a situation where you have two or more forces acting on on an object then you have a range of things that can happen. So for instance if those two forces in this case the pressing of my thumb and my forefinger are both acting towards the object then that object can be compressed as shown in the top corner here which is a deformation a change in shape. On the other hand if get this back into something like a ball if the object if a force is applied to either end away from the center of the object then the object will be stretched in this case broken but stretched to be longer. And the third option if you have an object if you have an object and you have three forces acting on it say one that way and then two this way then you can bend the object. So one force accelerates gets faster in a particular direction two or more forces and it's either going to stretch, compress or bend. Now in a later topic we're going to talk about a lot more about acceleration so what we're really interested right now is when we have two or more forces and we stretch, compress or bend the object. Now there are two types of change of shape. Remember we said deformation means a change in shape. There's elastic and plastic. Now an example of an elastic deformation would be this elastic band here aptly named because of the way it deforms. If I am if I was to stretch this elastic band and then release it it goes back to the original shape. Now there is a point beyond which it won't go back but we'll talk about that in the later video. So if something elastically deforms then it can go back to its original shape when the force is removed. Likewise with this elastic band if I press this elastic band in like this and I let go it returns to its original shape. On the other hand there's a type of deformation known as plastic deformation. So this is where an object I'm not going to attempt to stretch a steel paper clip but I will bend the steel paper clip. So this is where an object is deformed like that but when the force is removed it does not return to its original shape. Some materials much more easily undergo plastic deformation than elastic deformation and vice versa. So this steel paper clip it is possible to bend it just a little bit. Can you see that tiny little flex there? You can bend it a little bit and it will elastically deform it will return to its original shape if you apply a small force. On the other hand if you apply a slightly larger force then it'll undergo plastic deformation and permanently change shape. This elastic band under most conditions it will deform elastically returning back to its original shape but if I were to pull it far enough then it would undergo plastic deformation and although it will return to something closer to its original shape it will have it would have been stretched permanently by a small amount. If we go back to the ball of play dough it's very difficult to make play dough to form elastically. It would be an absolute minute force applied to make it elastically deformed with even a very small force applied you are making it plastically deformed. It does plastically deformed very nicely which is essentially why it's a toy for children but it certainly doesn't elastically deformed very easily at all. So it depends very much on the material and the structure of the material whether it will undergo elastic deformation or plastic deformation or combination of the two depending on the force applied. Now these two terms apply to bending, stretching and compressing. Well that's it for this video hope it helped, hope it is helped, goodbye.