New trends in physics teaching, v.4; The ... - unesdoc - Unesco

New Trends in Physics Teaching IV
The knee-bend game (energy and power)
The participants do a knee bend, and the distance from some suitable part of their anatomy to
the floor is measured. They then stand up, and the same measurement is made from this position.
Most people know their weight, so the work done, mgh, mass times the acceleration due to
gravity times vertical distance risen, is easily calculated. For example, if your mass rn is 50 kg and
the distance h risen on standing is 60 cm, the work is 50 X 10 X 0.6 = 300 joules. The work
performed on rising is not regained on sitting - unlike a bicycle running downhill, we do not
store the potential energy on doing a knee bend - it is lost as heat. Some student is bound to
have a watch with a second hand, so the next portion of the game is to see how quickly you can
do ten, twenty, fifty knee bends. The power is then the rate of doing work. If you do 40 per
minute, in the above example, the power would be 300 X 40/60 = 200 watts. Generally, the rate
of doing knee bends is about the same for men or women, but women weighing less, their power
is also correspondingly less. One can also perform a similar game running up and down stairs and
measuring the power required - however, one should avoid giving older students heart attacks.
The wave game
This one is great fun. Students stand in a line, fairly close to one another, and put their hands on
the shoulders of the individual in front. The one in front of the line rests his hands against a convenient
wall.The last in the line gives a hearty push to the one in front, who (to avoid falling)
pushes the one in front, and so on. This resembles the game played with a line of dominoes
placed on end. When the front is reached, a push is given against the wall,and the compressive
longitudinal wave travels toward the back. About the only problem in this game is attenuation of
the waves - a really good push is needed to avoid this. To simulate reflection at an open end, the
last person in the line pulls the shoulders of the individual in front, who pulls the shoulders of the
next in front, and so on. The front of the line, on being pulled back, and having no one to tug
on, falls back and ‘reflects’ the rarefaction as a compression. This is not as self-generating as the
compressive wave. The wave wil rapidly attenuate unless positive feedback is inserted - each
student, on being pulled back, must make a conscious effort to pull back the student ahead. I
have found, when the students see what is going on, that it makes understanding a difficult
concept much easier - and enjoyable!
Transverse waves can be simulated by the last student pushing the one ahead sideways. Again,
this travels to the front, where, if the student has nothing to hang on to, a reflection of the same
sign occurs. If the student hangs on to a doorway, or other solid object, the pulse is reflected
with change of sign. Another way to propagate transverse waves is for the students to hold hands
in a line, facing perpendicular to the line, and for the student at one end to start a wave which
wil travel to the other end. If the student at the far end is holding on to something, again the
wave will invert, but if not, it wil reflect with the same sign (or the student wil fall over). A
variation of this game is seen in ‘crack the whip’ played by a line of ice skaters.
Further suggestions for games may be found in the New Games Book [3], for example, for
statics, the pyramid game [3, p. 571, and the stand-up game [3, p. 651 are good. Interesting
suggestions for the way fundamental physical concepts apply in games wil be found in Peter
Werner’s book, Learning through Movement [ 41 .
Having found this concept works, you may be inclined to design your own games. One such
game in the middle of a long 70 minute class both wakens and relaxes the students!
338