jgourlay
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A question to educators about Potential Energy
All:
If you were asked to climb in your car and go visit a group of liberal arts oriented college freshman, and do a whiz-bang quality demonstration of
POTENTIAL energy, and do it in a way that they get the point, how would you do it?
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Magpie
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Drop a rubber ball onto a hard floor.
1. The potential energy is set depending on height of the ball above the floor before being dropped.
2. It is converted to maximum kinetic energy and zero potential energy just at the point of contact with the floor.
3. The KE is absorbed by compression of the ball. This is also a form of potential energy.
4. The PE of the ball is reconverted to KE and the ball rises to velocity = 0 and the PE of height is regained, except for the loss due to friction
which is converted to heat.
This is simple and elegant I think, but not whiz-bang. So it might be too boring for liberal arts students. 
The single most important condition for a successful synthesis is good mixing - Nicodem
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Bot0nist
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You could tie something heavy, like a bowling ball, to a rope to make a pendulum. Hold the ball against your nose and release it. It will never come
back and hit you due to PE > KE. Just don't give it a little push.
U.T.F.S.E. and learn the joys of autodidacticism!
Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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Ramiel
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Oh dear I thought the beginning of your question was part of the riddle, had my thinking cap on too early!
I always liked the elastic band demonstration... although that's really kinetic -> chemical energy I think
perhaps a purer way of showing it is to crank something to a height (chemical -> kintetic -> potential) and then letting it drop and do some
work. Knowing liberal arts college freshmen this might involve smashing an effigy of George Bush...
Caveat Orator
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The WiZard is In
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They will remember this... if not you.
And it has an added history lesson at no extra cost.
A single instance will serve to
display the rigor, and even
cruelty of Aurelian. On of his
soldiers had seduced the wife
of a his host. The guilty wretch
was fastened to two trees
forcible drawn toward each
other, and his limbs were torn
asunder by their sudden
Separation. The punishments
of Aurelian were terrible ; but he
had seldom occasion to punish
more than once the same offense.
Gibbons
You could use a hamster or rabbit or frog or....
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kryss
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The ball thing was done by Brian Cox in the BBC's "Wonders of the Universe" where he held pendulum with a big iron ball up to his face then released
it, watching it swing away then back again, stopping inches from its starting point.
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IrC
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Have them hold a bowling ball above their foot. Start at 1 foot up. Upon dropping the ball each time the pain gets worse as they hold the ball ever
higher. The pain will never leave their mind and explains the concept in a simple way they will instantly, easily comprehend.
Of course you can use a lighter, less painful ball just to be nice, the point being they will get it as it is already within the realm of their
everyday experience.
"Science is the belief in the ignorance of the experts" Richard Feynman
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fledarmus
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Well, if you really want them to get the point, hang a sword over their heads by a single hair. Being aspiring liberal artists, they should recognize
the reference, and with their attention firmly in hand, the power of potential energy should be relatively easy to convey...
[Edited on 12-7-2011 by fledarmus]
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sternman318
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Quote: Originally posted by The WiZard is In  | And it has an added history lesson at no extra cost.
A single instance will serve to
display the rigor, and even
cruelty of Aurelian. On of his
soldiers had seduced the wife
of a his host. The guilty wretch
was fastened to two trees
forcible drawn toward each
other, and his limbs were torn
asunder by their sudden
Separation. The punishments
of Aurelian were terrible ; but he
had seldom occasion to punish
more than once the same offense.
Gibbons
You could use a hamster or rabbit or frog or.... |
Or an unsuspecting volunteer !
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sternman318
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| Quote: Originally posted by Bot0nist | | You could tie something heavy, like a bowling ball, to a rope to make a pendulum. Hold the ball against your nose and release it. It will never come
back and hit you due to PE > KE. Just don't give it a little push. |
http://www.youtube.com/watch?v=CgqBg44azYk&feature=playe...
watch at 48:00
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peach
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The problem with potential is that it's a 'hidden' quantity, unlike kinetic, which seems easier for humans to accept (as they can see it 'happening'
in front of them); particularly people who learn kinaesthetically.
Maybe throw a bouncy ball at the floor and then ask why it falls back after climbing. They'll say gravity. Then you can point out that it must have
'stored' the energy somehow when it was slowing down mid air, and that we call that potential. It stored it by doing work against gravity and 'what
goes up, must come down' <- this latter motto will be something they already accept as a given, and that the ball WAS going to go back up when it
bounced, narrowing down the variables in their mind.
Another demonstration could be potential differences in circuits, with varying voltages having the potential to drive differing amounts of current
through the same resistance. This will only be interesting if it involves an arc for one of the demonstrations <- ask if they have a van de graff
generator (my secondary school had one but it was a technical school).
Charging capacitors up to differing voltages and then shorting them with a screwdriver will produce a good pop as the voltage (stored energy) goes up.
Using interactive or modern media is a big thing in schools now. All of the schools my family members teach in are having, or have, interactive white
boards in them, connected to a projector and computer. Even if they don't have a full sized board display, you could show videos from youtube of kV
capacitor discharges.
An important aspect in teaching is to appreciate that half to a third of the class might not like (get) one particular method of demonstrating
something, because not everyone sees how things function in the same way, or from the same angle. Doing multiple, quicker demonstrations in different
forms will likely work better than one in detail. It will also serve to reinforce that fact it is a universal form of energy found in every system;
not just a bouncing ball in a lame physics demonstration.
Some people are horrible at understanding it from a practical aspect and much prefer the theory on the board. And vice versa. Given that they're
towards the arts, I expect a larger percentage of them will 'get' the practical explanation over the board theory.
There are, of coarse, multiple forms of potential energy, subdivided into kinetic, chemical, electrical and so on. A nuclear bomb has a stored
potential. Unfortunately, chain gunning bullets into the air from an AK47 and screaming like Rambo may be frowned upon in a classroom environment.
In our classes, health and safety had hit the physics labs, and (aged 16+ in a rapidly diminishing class size) we had to wear safety googles to
stretch elastic bands when finding their elongation and tensile strength values. We'd done the old fizzy drinks bottle rocket and bike pump
demonstration two years earlier. The first attempt died on it's arse when the arse of the bottle dropped out before pressurising. Being an all boys
school, and a young male teacher, that was entirely unacceptable. Attempt two worked so successfully the bottle rocketed a hundred feet or so up to
the roof to the building, where it landed and retained it's kinetic PE, thus ending the demonstration. The bottle rocket is good (although they would
prefer something involving an actual rocket engine) as it's more exciting than the ball. Arguably too exciting as they will be focused more on how
cool it is than what's happening in terms of the physics. I would recommend the bottle rocket, but start with stretching a ban and flicking it upwards
and then the bouncy ball so they have something to look forward to.
You may have issues with health and safety over the bottle rocket, an actual model rocket engine will be harder again. You'll want to speak to a
member of staff about those options. Whipping a model rocket out unannounced is unlikely to go down well.
You could come in from the rocket and go onto the different forms of potential, like the chemical potential in a stick of dynamite (holding a stick of
dynamite made out of cardboard tube painted red ACME style, and tossing it to indicate it also has kinetic potential as it is) and show some quarry
blasting, tying the flying bits of rock into the bottle rocket, the stick you're tossing in your hand and how the chemical potential has changed to
kinetic potential as the rocks hang in the air before falling back to the ground.
<iframe sandbox width="640" height="510" src="http://www.youtube.com/embed/aCJwFoaKdhQ" frameborder="0" allowfullscreen></iframe>
These are educationally worthwhile and more appropriate than nuclear bombs or diy explosives as they do not directly suggest making explosives, they
are not weapons and they are related to something that is industrially worthwhile (mining).
<iframe sandbox width="640" height="510" src="http://www.youtube.com/embed/9BzUph9HvZk" frameborder="0" allowfullscreen></iframe>
<iframe sandbox width="640" height="510" src="http://www.youtube.com/embed/SmKbdOeb-Mg" frameborder="0" allowfullscreen></iframe>
And then electrical potential with these.
<iframe sandbox width="640" height="390" src="http://www.youtube.com/embed/gj1pkyCL75E" frameborder="0" allowfullscreen></iframe>
<iframe sandbox width="640" height="510" src="http://www.youtube.com/embed/PXiOQCRiSp0" frameborder="0" allowfullscreen></iframe>
This one may be deemed inappropriate, as it is not hard to replicate once they know how it's done, yet ridiculously dangerous and criminal. Actually,
it is hard to replicate without incinerating oneself.
<iframe sandbox width="640" height="510" src="http://www.youtube.com/embed/8V3OZMW_45M" frameborder="0" allowfullscreen></iframe>
Here, potential is stored both in the weight of the hammer and the compressed gas in the rams. And the glowing lump of metal.
<iframe sandbox width="640" height="510" src="http://www.youtube.com/embed/gq_OU1fALcA" frameborder="0" allowfullscreen></iframe>
Hopefully this will be metaphorically occurring in their minds towards the end of the lesson.
<iframe sandbox width="640" height="510" src="http://www.youtube.com/embed/hORUSzOvUfM" frameborder="0" allowfullscreen></iframe>
[Edited on 17-7-2011 by peach]
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