"Counting calories in the
First of all, it’s
“pop” here, not “soda”, “Coke”, or “sodee”. This may not be true in your
area. Check the indigenous population.
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) * (mass of substance in grams) * (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.
Here's a photo from our calorimeter experiment; burning
up Lays chips. We used the EasySense Datalogger to keep track of the
temperature changes over time.
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.
TRY IT! This complete demonstration lesson
is available here.
Ever wish you could bottle the
energy young children bring to school? Now you can use it to help them
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.
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
about using it to power a Constant Velocity Car, instead of batteries? (Or
use the car to power the Genecon!) How about using the Thermoelectric
Device and turning the electricity generated by the Genecon into heat? or
cold? (OK, removing heat). 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.
… the sky. No, really.
Ok, the “Watts Up?” is really a
meter. You 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.
From last issue…
Sugar - is there a link to
Sugar provides energy. Does it also increase strength?
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.
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.
Cool online Resources
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