Take an empty can. It needs to still have its ring. Fill the can about 1/3 full with water. Pull the ring up so that it is vertical. Put a glass rod or similar through the ring and suspend the can through the ring of a ring stand. Be careful so that the rod does not slip off. Use tongs or forceps to hold a small piece of potato chip. Light the chip with a match and hold it under the can. The water heats up. Use this equation to find the amount of energy stored in the chip (or pretzel, peanut, whatever).
Heat gained or lost = (specific heat of substance) x (mass of substance in grams) x (temperature difference)
(Remember, the substance of interest here is the water because its temperature is easy to measure.) The specific heat of water is 1.00 cal/g*degree. Heat energy is measured in calories. Remember that a food calorie (or Calorie) is 1,000 calories (the amount of heat energy required to raise the temp. of 1 g of water 1 deg. C).
Experiment idea: Try regular versus baked chips.
Energy conservation in a "Stopped Pendulum."
Here's an interesting demo to show potential energy and the conservation of energy. Make a pendulum by hanging a mass from a string. Put a barrier in the path of the string, as shown in the diagram. The pendulum swings down and the string effectively becomes shorter as it strikes the barrier. How far up will the mass swing? Lower, higher, or the same level as before? The mass still rises to about the same height. Put a board behind the pendulum and mark the starting height, or put it in front of a chalkboard, so that you can show that the heights are about equal.
Generators and Motors
Ever wish you could bottle the energy young children bring to school? Now you can use it to help them learn!
Generators and electric motors; there are basically the same thing. But sometimes this simple concept is lost on some students. The Genecon hand-generator can be used to study all kinds of energy issues. Supplying up to 5 volts, it acts as a generator when you turn the handle to create an electric current, and as a motor when you supply current that causes the handle to turn. The most obvious experiment is how much mechanical energy does it take to power light bulbs. Students can really feel the increase in their effort as you add more light bulbs to the circuit. Even young children can make the connection between more light bulbs and needing more energy to power them.
How about using it to power a Constant Velocity Car, instead of batteries? (Or use the car to power the Genecon!) Use it instead of batteries to power all kinds of 4-6V devices. Figure out how efficient the Genecon is by powering one by another. Count the number of times you turn the handle and how many turns you get from the other handle. Challenge students to figure out where the lost energy went.
You can plug it into a standard wall outlet and plug an electrical device into the meter. The meter will show you how much energy you are using and how much you have used since it was plugged in. You can even set the rate so you know how much you would pay for that much electricity.
This is a great tool for units on energy conservation. Compare different appliances. Compare different sized light bulbs, or incandescent vs. Fluorescent vs. Halogen bulbs. Challenge students to identify which device in a group uses the most electricity, and test their hypotheses.
Sugar and Strength
Sugar – is there a link to strength?
Sugar provides energy. Does it also increase strength?
Have the students perform a strength test. It can be arm wrestling, lifting weights, or something else that makes them use almost all of their strength (at least in one limb). Have them take a pinch or cube of sugar and put it into their mouths. Try the strength test again. They will be amazed at how much less strength they have. This works especially well when they are testing themselves near their limit. For instance, I did this with a student where we were dead even in arm wrestling. He took the sugar saying, "Now I should win quickly." When I won quickly instead, he was shocked.
OK, but what's happening? That's not entirely clear. The effect is too quick and too drastic to be from digesting the sugar. What seems to be happening is that there is a feedback somehow to the brain. You taste sweet and the brain responds. Challenge the students to explain what they've observed. Consider working with a biology teacher to help students make the connection between physical and life sciences. Note: this experiment does not work right after lunch or after the students have had something sweet.