my third grader needs to make a simple machine for science class, have any ideas?
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A lever is about as simple as they come. Its used to help lifting heavier objects.
You could do this on a smaller scale with a short plank of wood and simulate a doll lifting something much heavier than itself (such as the toy box it comes in). Place the pivot point very close to the heavy object. (a pivot point is just something that will raise the plank off the ground and allow it to move, you may want to attach it to the plank)
You may need to experiment with different lengths and weights in order to get your heavy object to move. The longer the plank the easier it is for the light object to move the heavy one.
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Whoever rules in hell is still in hell, but they won't rule for long.
The next of Archimedes' 4 basic machines is the inclined plane. A screw is the easiest example to build since you can get all-thread and nuts to fit at your local hardware store. Be sure to note that screw-locked levers can accurately repeat operations virtually infinitely. That is how cabinetmakers get cuts to within .0003" every time. And when you re-set the stop, the machine will repeat its function to that point, time after time.
The third of Archimedes machines is the wheel -- a mathematical extension of the lever. The clever use of ratios in wheels fixed to a load (otherwise called a block and tackle, which is also easy to build at home unless you just haul off and buy one).
(rarely noted) the ratio-pump is another of Archimedes' gifts to engineering. One side has a large area, giving greater volume, the smaller has greater pressure, all with the same weight on the piston in a tightly-fitting cylinder. Engineers use that in air compressors. Now, if you want to show something truly impressive, build a tiny air compressor from junkyard parts. Use an old piston-type air conditioning pump, remove the flow restrictor in the intake, and there you have the beginning of a nice little 1-1/2 HP compressor to fill your tires at home, or blow dust off your clothes, or operate air tools, or . . .. Next, show a cutaway pneumatic actuator. Demonstrate the synergestic power of compressed air with a nail gun, available at your local hardware store, or an air motor, that will lift an unbelievable amount of weight -- about 4.5 times the power you put into that system. If you want to go even farther, talk about adiabatic comperession versus isothermal compression -- which would be a good middle-school project, and will definitely get an A. The math is a bit involved, which if shown, will get your kid serious notice by MIT. They like to see kids who take a heartfelt interest in engineering.
Another science project for young-uns is the rotary pump. Use clear acrylic to fashion the parts, and voila, you have not only built a machine, but you can also use it to show the value of integral math. Turn the pump slowly, and it moves hardly any liquid. Move it faster, and it delivers far more than the increase of your pumping effort. Move it faster still and the result is hard to believe. Hence, you now see why modern machines all use hydraulic actuators. You will also see some math that will really open your eyes. There is just no negative side to this equation.
Safety first! That does NOT mean "err on the side of caution." Your kid is smart enough to follow OSHA safety regulations -- and the sooner he learns that, the safer you will all be at home. Learning is a family activity. While you teach your son how to live safely, you will also pick up on ways to minimize hazards in your home that you may not have known existed. When you know what your actual hazards are, then you can intelligently correct them.
For example: are all the containers in your home labeled with the ACTUAL contents? OSHA rules are that you must label ALL containers with their contents, intended application, and product hazards. Salad oil, for example, can be as flammable as gasoline when heated over 375 degrees F. It is still safe to use, but know the hazard and keep a box of baking soda handy to snuff any fires that erupt. If you really want to be safe, get a 10-A,2-B-C fire extinguisher and keep it in the kitchen. We sure do.
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