comparing (and contrasting) a 'spring scale' and a triple beam balance.
Yes yes yes yes.
In more detail:
Physical principle: the triple-beam balance measures mass. It does so by
comparing the unknown to some known masses.
Physical principle: the spring-scale measures force. It doesn't care
whether this is a gravitational force, or some other kind of force. It
cares nothing about mass _per se_.
=====================================
This reminds me of the first original scientific experiment I ever did. It
was 1960. I was 5 or 6 years old. Nobody had ever been in orbit. Nobody
had ever been weightless long enough to get hungry or thirsty. But
everybody was talking about such things. I read in a book that space
travellers would have a hard time eating and drinking, because there would
be no gravity to help food go down the gullet.
I didn't believe the book. I decided to do the experiment. I couldn't
produce zero Gee, but I figured -1 Gee would tell me what I needed to
know. I got a glass of milk and a straw, and went outside on the porch. I
did a handstand, propping my feet against the wall next to the mailbox. I
put my mouth around the strategically-positioned straw and took a gulp. No
problem. Waited for a moment. No sign of milk coming out my
ears. Decided to drink the whole glass. No problem. Zero Gee was
certainly not going to stop astronauts from eating and drinking.
=======================
Here is why this story is relevant:
1) You can use a balance-beam to make a mass-to-mass comparison in a way
that is independent of gravity. Firmly attach a massive object to one end
of a sturdy stick and a less-massive object to the other. Drive a pin
through the stick at the balance point. Grab it by the pin. Show that it
balances. Turn it upside down. It still balances. This is -1 Gee. Shake
it up and down. It balances no matter what the local gravitational and/or
other acceleration is. It would work just fine on the moon. It compares
mass to mass under all conditions (although its sensitivity goes to zero
under conditions of weightlessness).
2) Now firmly attach a weighty object to the active end of a
spring-scale. The "fish scales" they sell at the boat store are good for
this. Note the reading. Then shake the frame of the scale up and
down. Note the wild fluctuations. Flip the thing upside down, and observe
that it reads less than zero.
================================
This reminds me of another childhood physics experiment:
When I was seven or eight, we visited the Old Tucson movie studio. They
had an old-time railroad car sitting there. For a joke, my kid brother and
I posed as if we were pushing the railroad car. Somebody said "that's
ridiculous" and we took it as a challenge. So we spent the next several
minutes pushing really hard. It turns out that railroad cars have very
good bearings. If a couple of kids push for long enough, they can pour a
huge amount of momentum into the thing. It was several minutes before
anybody but us noticed what was happening. My mother said "Hey, where are
you going with that railroad car?"
By this time the car was moving right along. It wasn't moving very fast,
but it was definitely moving, and it showed no signs of stopping.
We ran around to the other end and the two of us, plus our father, pushed
on it in the opposite direction. It took a long time to get it stopped.
Why is this story relevant?
It might be good to let all physics students try their hand at this
experiment (with suitable safety precautions). Set up a car on a deserted
level road, and let people push it. Maybe it would be safer to pull it
with ropes, to reduce the risk of anyone falling under a wheel. You can
get it going pretty fast, but you have to push for a long time because it
is so massive.
The words that go with this lesson are that the weight of the car is
irrelevant (to an excellent approximation); the weight is cancelled by the
upward force of the road on the wheels. But the mass is still there. The
inertia is still there. If you wanted to push the car along an
equally-horizontal lunar road, it would require just as much effort. The
weight would be 6x less, but the weight would still be irrelevant. The
mass (plus a little friction) is what you are feeling when you push it
horizontally.
This also gives them a feeling (literally) for orders of magnitude. Toss a
US nickel coin more-or-less horizontally from hand to hand: This is what 5
grams feels like. Shove on the car: This is what a megagram feels like.