Hello team! Looking forward to working with all of you this year as we explore mechanical sciences. All the science expectations for this competition are also in the grade 8 curriculum and will be taught in class while you are getting extra hands-on work while practicing for the actual competition held at the end of February. It is a long and tough day, but its fun too and an experience you will not forget. The competition takes place at the Ontario Science Centre in the Great Hall. Your parents are welcome to come watch or be present for the presentations at the end if they can make it (but they will have to pay for their entry). Lunch will be provided, and you will take home a new pair of safety goggles! You only have to bring your best mechanical science game!! Simple Machines - How they work.Consider the notes about WORK, FORCE, and DISTANCE from the package I handed out in class. In Science, WORK is the amount of FORCE exerted over a specific DISTANCE. For example, if I moved a 100N load, 2m, I would have done: 100N x 2m = 200N/m or 200Joules of work. When you think about ancient Egypt or ancient China, we are not only amazed at the mathematics involved in building the Great Wall, or the Pyramids, but we also marvel at how these people were able to lift and carry these immense stones great distances (in other words do large amounts of WORK) without machines! The reality is however, is that they DID use machines! They just didn't use the modern machines we know of today. They used simple machines. These simple machines work by changing the balance between FORCE and DISTANCE when doing WORK so that with human strength alone, large forces could be carried (but at a cost!) This might seem confusing now, but you will understand once we are done here =) Lets start from the beginning.... Basically there are 6 simple machines that you have heard about over the years: lever, wheel/axle, pulley, wedge, ramp or inclined plane, and screw. When you look at all of these, you will find that even more basic than that, there are really TWO simple machines: the LEVER and the INCLINED PLANE. The other machine's are just variations of these. Anything round, is just a bunch of levers put together spinning around a fulcrum.. and a Screw is basically an inclined plane wrapped around itself where a wedge is an inclined plane turned sideways! When you think about modern day machines, ANY kind of machine, you will realize that they are designed to make life easier. Imagine having to dig out a giant hole to build a house with a basement. We made a machine for that! Yes, we use the energy of oil/gas to power excavators/diggers, instead of our own energy to dig out a hole with a shovel and our backs, but an excavator also uses physics to help make that work more effective. Watch the following videos to see how a simple machine can give us a force advantage (gives us the ability to lift more). What is the disadvantage? When we use certain types of machines, we can lose energy we use in the form of friction, which turns our energy into heat and sound energy. The presence of Friction causes our machines to WASTE energy. More friction = LESS efficiency! Watch the video below. To sum up this section (which you will also be learning in class).... Machines are designed to solve problems. When building machines you need to consider what its purpose is. Will it need to lift/move a heavy load? Or does it need to move a load a great distance? Depending on your answer to this question, it will determine the design of your machine. Some machines designs will allow you to life a large load easily, but the trade off is that you have to move it a greater distance. Some designs will allow you to move an object great distances, but the trade off will be you need to use more force to move the object than normal. Notice that there is always this TRADE OFF> Remember that you can NEVER get something for NOTHING!!! |
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