Allright guys so you knew I wouldn't be able to get through this lesson without doing something related to Star Wars so we're gonna take a look at how forces act upon a structure, through this activity called may the force be with you.
So as we go through this we're going to see different types of forces caused by gravity, as well as caused by human interaction, that would serve allow for structure not to be as strong as it should be.
So the floor are called tension, compression, torsion and shear; and there are very sciency words, but I can promise you that they are not that sciency once we see them in action we're going to see how these forces act upon this book on the right here so instead of tension
- So tension is a force that stretches or pulls in opposite directions, so in the example here, we have two people play tug-of-war over book, and really tug of war is a perfect example of tensión. You're creating the tension on that rope and you're trying in the case of tug-of-war to get the other team to fall off balance and get the Rope more in your direction. We see this happen in cable style bridges so the Vancouver sky bridge, as well the Golden Gate Bridge maybe a little more familiar to you. So we see these wires, which are by tension holding this bridge up. Okay?. Sometimes we call these suspension bridges as well
- If we look at compression. Compression is the force being created by gravity really, so it's the pushing down creating you know damage or creative force and really weighing something down. Sorry time you sit on a couch our bodies compress the foam in the springs we also see compression act upon support columns, so we see that example right here. Okay? So in ancient Greek architecture we see a lot of columns ancient Greeks were very good at building and architecture and they serve discover called as being this great way to use force its court wait.
- Torsion is like a twisted, so when you have to bring it a sponge you're you're using torsión to expel all the water from inside that sponge. Okay? We also use torsionally twist open a jar so jar of peanut butter or pickles in this case
- And lastly shear. So shear is the idea of in this case ripping a page out of a book okay when a structure is torn or ripped it is usually as a result of sheer force so in the case of shrubbery okay we use shears to prune the hedges to look the way we want.
So we have a number of different examples here we're just going to apply the proper one, so we'll give you a free throw and I'll give you a couple seconds to think in your head
- So the first one is a turning or a twisting forcé. So I want you to think back to that sponge example, that would be your torsión
- A force that stretches or pulls in opposite directions so think of that tug of war that would be tension
- A force that pushes and or poles portions of an object in opposite direction so it sat opposite directions that should be the indicator here that we're talking about shear
- And lastly a force that squeezes or pushes on something process of elimination, is compression
Okay, so here's those examples again. Give you a couple seconds so what would you think for this first one here we have forces pushing down. Is that compression, tension, shear or torsion?
That would be compression
We have that ripping, so think of when you're pruning hedges you use some shears. So that is a shear force.
remember that tug-of-war creates tensión and that spongy one is called torsión
okay? So we're not going to worry too much about this we might worry about it in class, but I want you to keep those different types of forces in mind for when you come into class on Wednesday
