Intro Quiz: Robert Hooke and uses of elastic objects

Video: Robert Hooke and uses of elastic objects

﻿Hello everyone and welcome to this lesson. This is our ninth lesson in our Forces in Action topic. Before we start, all you need is a pen and a piece of paper. So please pause the video now to make sure that you have those with you. You might also want to go somewhere that's quiet, where you're not going to get distracted, and you can really focus on our lesson today. So once we've done that, let's get going. There are going to be three main parts of our lesson, and then there's an exit quiz you can do to show how much you've learnt. In the first two parts, we're going to talk about Robert Hooke's life and discoveries. And then the third part, we are going to talk about some uses of elastic objects. Robert Hooke was born in 1635 and died in 1703, that means he lived about 350 years ago. He was born on the Isle of Wight, which is an island in the South of England. After that he went to do his studies at Oxford University, there he met lots of future famous people. One of them was Robert Boyle, who he worked for. He made the equipment for Robert Boyle, who is now a famous scientist. And Robert Boyle used this equipment to discover some of his famous laws. After that, he moved to London where he became a fellow or a member of the Royal Society, which is the most famous society of scientists. While he was there, he also became something called the Curator of Experiments at the Royal Society. This was the first time a scientist got a full-time job as a scientist. His job was to make equipment for experiments, for both his own theories and to test the theories of the other scientists for them. Another person who was a scientist at the same time was someone called Isaac Newton, who you might have heard of. He's now called Sir Isaac Newton. However, despite both being scientists, they were quite competitive and they had a bitter rivalry. Sadly, Robert Hooke felt like lots of his discoveries were ignored and that other people got the credit when he should have done. And so he became quite a bitter person and he died on his own in London in 1703. Robert Hooke contributed to lots of areas of science because in those days, science wasn't split into the different categories that it is now. People were just scientists. And so let's have a look at some discoveries Robert Hooke made. Robert Hooke made lots of contributions to timekeeping and one of them is the pocket watch. The pocket watch was the first way people were able to tell the time on the move. It uses something called a balance spring. And Robert Hooke combined his ideas of elasticity with springs, with the ideas of forces and other types of mechanics. And he combined those to make the pocket watch. He also was one of the first people to use a microscope and he pointed the microscope to very small things in this case, some wood or cork. And what he discovered was that the wood looked like tiny little honeycomb cells. And because of that, he called those little sections of wood, cells, which is why we now call the building blocks of life, cells in biology. Robert Hooke contributed to gravitation as well. He was one of the first people to suggest that a force was required in order to change the direction or speed of an object. He also contributed to astronomy or astrophysics, and that means the study of space. He wanted to find out the distance to a certain star. We now know that his result is wrong because his equipment was very imprecise, so he was quite a way off. Robert Hooke, also, was interested in palaeontology, which means the study of fossil. Robert Hooke studied fossils and said that he thought we could use fossils to learn about the history of the earth. Robert Hooke was assistant to Sir Christopher Wren, a famous architect, right after the Fire of London. After the Great Fire of London, Sir Christopher Wren was asked to rebuild and redesign London, which he did. And Robert Hooke helped him. Let's see if we can remember anything about Robert Hooke. Which of these areas did Robert Hooke not contribute to? Five seconds. Robert Hooke did not contribute to jazz, so well done if you got that right. What word did Hooke you use to describe the sections of wood? Five seconds. He used the word, cells. What does palaeontology mean? Try saying it five times quickly, palaeontology, palaeontology, palaeontology. Five seconds. It means the study of fossils. Really well done, if you've got that right. Or if you can just say the word, because it's quite long, what do astrophysicists or astronomers study? Five seconds. They study space. Really well done, if you got that right. Now, let's have a look at some uses of elastic objects. Let's look at a reminder of previous lessons. Remember that elastic objects return to its original shape after a force is removed, if the force is below the elastic limit. So there's a point where if the force gets larger than, it won't be elastic anymore. And we call that the elastic limit. Force and extension are directly proportional because at the beginning, there's that straight line through the origin. But only up to the limit of proportionality, which is where it starts to curve. A larger spring constant means a larger force is required to change the shape. If I have a large spring constant, I need to really pull hard to change the shape or really push hard to change the shape. But if I have a small spring constant, it's really easy to make the extension bigger or compress the object. One use of springs is in watches, another is a pogo stick, a trampoline. This is the inside of a spring mattress, so normally we can't see that part, it's normally covered. But this is what the inside with the springs might look like. And also elastic objects are used in a bow and arrow. Let's have a look at how the bow and arrow works. When I pull the spring on the bow, I am exerting a force on the bow. The force moves the string and stretched it. This means work has been done. And if work has been done, energy has been transferred. The energy has been transferred to the elastic potential energy store of the string. So because there's a force that stretched and moved the string, that means work has been done. And so energy has been transferred to the elastic potential store of the string. If I let go of the string because it's elastic, it's going to bounce back to its original shape. And that means that the elastic potential energy store is going to decrease. Because if it's not stretched anymore, then there isn't any energy in the elastic potential store. For energy must be transferred somewhere from the elastic potential store. And it's going to be transferred to the kinetic energy store of the arrow. And so the arrow is going to fly off because its kinetic energy store has been increased. If my arrow is going a little bit too slowly and I want it to go a bit faster, I might use a string with a larger spring constant. This would mean I would need to use a larger force to extend it. And a larger force means more work done. And that means that there'll be more energy transferred to first of all the string and then to the arrow. Lets now try explaining this step by step using some multiple choice questions. When we extend or compress an elastic object a force is required, this means? There are two correct answers. You have 10 seconds. This means work is done and energy is transferred, well done. This energy is transferred to the something store of the object, five seconds. It is transferred to the elastic potential as we stretch or extend an object. The elastic object will what, when we let go? Five seconds. The elastic object will return to its original shape. This means its elastic potential store of energy will? It will decrease. If it returns to its original shape then it's not extended anymore and that means that the elastic potential store has decreased. In a bow and arrow, this energy is transferred to? 10 seconds, this time. It's transferred to the kinetic store of the arrow because it shoots the arrow off. So the energy goes from the elastic potential store to the kinetic store of the arrow. So really well done, if you managed to follow along with that. Now, it's your turn to do this completely independently. Please describe how a slingshot can launch a rock. There are some key words on the screen, so please pause the video now to have a go. If you want some extra help with this task, you can do it this way, simply fill in the missing words. Hopefully you had a go either using the help on the screen now or completely independently. Let's have a look at the answer. The first point is that force pulls the rubber band, this means work is done. And so energy is transferred to the rubber band. The elastic potential store increases. When we let go, the elastic object will return to its original length. This means energy will be transferred from the elastic potential store to the kinetic store of the rock and it will move. So really well done if you managed to answer that question, 'cause it was quite long. You might want to pause the video just to make sure that you've understood this question. Next, we're going to talk about how spring constant might affect the uses of elastic objects. If a spring constant is too low, that means that for a given force, there will be too much compression or extension and not enough energy stored. If a spring constant is too high, that means that for a given force, there will be too little compression or extension. Let's see how this applies to a spring mattress. If the spring constant is too high, then there will not be enough compression, so it will be uncomfortable and it'll be too sort of hard. If the spring constant is too low, then there'll be too much compression and it will just sink and it'll be really hard to get out of the bed. Let's recap, a high spring constant means? There are two correct answers, so 10 seconds. A high spring constant means that you need a very high force in order to extend and there will be a lot of energy stored. So really well done, if you got that right. What about a low spring constant, what does that mean? 10 seconds. A low spring constant means that you need a low force to extend or compress it and that there won't be very much energy stored. So even though you can extend it by quite a lot, you can't actually store very much energy 'cause the spring constant is very low. Now, let's apply this to a trampoline. What would happen if the spring constant was too high or too low? If the spring constant is too high, then there won't be enough extension. So you won't really be bouncing and you might even hurt yourself. If the spring constant is too low, then there'll be too much extension and it won't spring back. So we'll just sort of sag in the middle. Now have a think about what would happen if an elephant got onto the trampoline. Well, the elephant has a really big force, doesn't it? So that means it's probably going to reach the elastic limit and if it reaches the elastic limit, it means that it won't be elastic anymore and there will be permanent deformation. So it won't spring back to its original size. So elastic limit will be reached and there will be permanent deformation. Here is another independent task for you to do. Read each point carefully and answer each part. Try your best, there are some key words on the screen to help you. Here are the answers. When you jump on the stick, the spring compresses and the elastic potential store of energy is filled. If the spring constant was too high, then the spring would not compress and so the man could not bounce. If the spring constant was too low, the spring would compress, but not spring back, and the man would not bounce. When the stick springs back up, the energy stored in the elastic potential store is transferred to the kinetic store and the gravitational store. So really well done, if you tried your best at that, I know it was quite tricky. Why don't you pause the video to make sure you can go through this step by step really carefully. Well done for getting all the way to the end of this lesson. I hope that you enjoyed it and that you learned a lot. What you can do now is go and do the exit quiz to show how much you've learnt. I hope that you join me for the next lesson as well.

Worksheet: Robert Hooke and uses of elastic objects

Exit Quiz: Robert Hooke and uses of elastic objects

Completed: Robert Hooke and uses of elastic objects

In this lesson we learn about Robert Hooke's life and other discoveries. We also discuss uses of elastic objects and how different spring constant effect how useful they are.

Science

Robert Hooke and uses of elastic objects

Introductory Quiz

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Worksheet

Final Quiz

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