Physical Science - Mechanical Energy

[Music] [Laughter] you [Music] which of these actions is an example of mechanical energy [Music] how are they alike [Music] how are they alike well that solid toe is a collection of molecules all moving together to exert a force the molecules don't have to be in a solid state the molecules can also move together to exert a force in a liquid state even air which is a gas can push each kind of mechanical energy seems quite different but they're all alike molecules are acting together to exert a force or a scientist say to do work [Music] when an orange juicer goes around the input of mechanical energy comes from a solid surface of ridges breaking up the orange to let the liquid out how is that input of energy different from the input that produces liquid from an ice cream cone well it's heat energy that causes the molecules in the ice cream to move faster and change from a solid to a liquid let's call out the molecule truce to see if we can make that clear okay molecules how are you in a solid state ready to turn into that orange are you ready orange molecule okay turn on the juicer input mechanical energy how does this differ from heat energy they're both moving molecules okay molecules what state are you in Berlin but when you feel the radiant energy from that whole Sun up in the sky doesn't making you okay we're going to take for even more radiant energy into heat energy now what does that make you turn you into a liquid straight input heat energy output a solid changes to a liquid the energy comes from the separate movement of each molecule vibrating faster whereas in mechanical energy the molecules all operate together to do the work [Music] as you may know if you've ever tried to lift anything gravity exerts a strong force when you lift water to a high position you've created a potential for that water to do works scientists say that it has potential energy okay I got it come on down now when the water is released it's pulled down by the force of gravity when it's moving it has kinetic energy you can run a turbine which can run an electric generator which can do work homemade electricity this is the same principle of course that we use when we build a dam for the purpose of making hydroelectric power potential energy kinetic energy and when you make it at home it's free free uh uh if you had to carry all those buckets of water you wouldn't call that energy free [Applause] knowing how to use mechanical energy makes a great difference in people's lives for centuries they've known how to use the energy of the wind of air molecules in motion a hundred and fifty years ago if people hadn't been able to use the wind to pump water farming would have been very hard indeed a window is beautifully simple the force of the wind is transferred through gears to a crank the crank makes a rod go up and down which pumps water to the surface the energy is free it strange that more farmers don't use when those today we've begun to transfer the mechanical energy of air molecules to electrical energy but the problem with wind energy is that sometimes it doesn't blow very hard and sometimes and not at all there's another very different way that we use the mechanical energy of moving gas molecules when fuel is burned the heat energy turns the fuel to a gas as the gas molecules expand suddenly they can be used to exert an enormous push [Music] and then we use the mechanical energy of moving gas molecules for small jobs jobs such as cooling off or making liquid evaporate or having fun what about the mechanical energy of moving liquids well people have been using that for centuries to almost always this form of energy comes from water pulled by the force of gravity one common use of water power in earlier times was to turn a mill wheel to grind grain under a heavy stone but to use this kind of energy everything had to be built next to a stream even factories it's much more convenient to convert the mechanical energy of the water into electrical energy the water turns an electrical generator wires carry the electricity cross-country to wherever it's most convenient to have the factory in this case the electrical energy is being transferred back to mechanical energy to do work the problem with using the energy of flowing water is that we're running out of places to dam our large rivers so increased use of water power is limited except for small jobs for having fun that leaves the mechanical energy of solids one of the reasons that our lives are so much easier than for people in earlier centuries is that we've developed so many new ways of using mechanical energy we still use the mechanical energy of our muscles to do many jobs we move lift carry hold open turn big cut sweep push today all of these kinds of work can be done by machines starting with other kinds of energy and transferring them into mechanical energy push sweet cut [Music] d turn open o lift Carrie [Music] we're so used to all these ways of using mechanical energy to do work that we don't stop to figure out how they do the work [Music] one of the most important machines for applying mechanical energy is an internal combustion engine it's so important that we ought to understand it the principle is based on Pistons which are forced down repeatedly so that they make a crankshaft turn this is one of the Pistons which travels in a cylinder this is the crankshaft that is turned a valve opens here to let in a mixture of fuel and air while the piston travels down as the piston moves up the cylinder it compresses the gasoline and air at the top of the cycle a spark from a spark plug ignites the fuel causing an explosion the expanding gasses force the piston down turning the shaft this is heat energy being converted into mechanical energy an exhaust valve opens here so that as the piston comes up again it pushes the gasses out this makes room for the next intake of fuel and air a diesel engine operates in much the same way as a gasoline engine in either case they turn a rotating crankshaft whose motion turns wheels or does other work we use machines to make work easier they transmit force and when they transmit force they often give us what we call mechanical advantage for instance you could pull all day on a nail without moving it but you can pull it out easily with a lever a lever is a simple machine two kinds of levers multiply and give greater mechanical advantage in a first class lever like this the fulcrum is here the force is exerted here and the work to be done the resistance is the staple in a second class lever the fulcrum is on the other side of the resistance and this believe it or not is a third class lever the force comes from the white hand the fulcrum is the left and the work is done by the end of the bat you hope a third class lever gives you speed and distance rather than increased force of all the simple machines the lever and the wheel and axle are probably the most useful in giving us mechanical advantage like the lever the wheel and axle can multiply force giving greater mechanical advantage or if you shift gears you can increase speed and distance on a bike you gain speed and distance since each step on a pedal takes you faster and farther than a step when you're walking but as you shift to a lower gear you increase force and cut down on speed and distance when you multiply force you gain mechanical advantage you [Music] every day of your life you need to make things move and most of the time to make things move you use mechanical energy [Music] [Music]