Unit 6: A Property of Matter (Mass)
Meador’s Inquiry Physics
Page 1 of 4
INQUIRY PHYSICS
A Modified Learning Cycle Curriculum
Unit 6:
A Property of Matter (Mass)
Sample Notes
I recommend that you always write out notes,
by hand, on the board for each class. That
allows you to control the pacing and focus,
rather than having students ignore you while
they simply copy down the content of a slide. It
also controls your pacing, so that you don’t race
ahead but instead focus on student
understanding.
©2010 by Granger Meador
inquiryphysics.org
Unit 6 introduces the concept of
mass, relates it to weight, and
then develops that mass is
inversely proportional to
acceleration. Do NOT use “mass”
until you get to the discussion
phase of 6 Lab A.
Ask frequent questions of students to check
their grasp of the material, and call upon
students to provide the next step when working
examples.
My rule for students is that if I write it on the
board, they must write it in their notes, and I
grade their notes each quarter and take off for
any units with incomplete notes or examples.
Trigonometry-Based Physics
(AP Physics B)
This unit is identical for both algebra and trigbased courses.
Unit 6: A Property of Matter (Mass)
Meador’s Inquiry Physics
Page 2 of 4
Sample Notes for Unit 6: A Property of Matter
Unit 6: A Property of Matter
mass (m) =
amount of matter comprising an
object (think protons, electrons, and
neutrons; NOT volume)
The notes don’t begin until after the
discussion of 6 Lab A. So now the students
have begun the process of distinguishing
weight and mass.
measured in kilograms (kg) or slugs (sl)
volume (V) = amount of space occupied by an object
measured in liters, cm3, in3, etc.
weight (Fg) = force due to gravity on an object
measured in newtons (N) or pounds
(lbs)
density (ρ) = mass/volume
measured in kg/m3, sl/ft3, etc.
We complete the Example 6-1 table as a
signaling exercise where I pose the
situation (using a Nerf ball prop), have
them think, and all signal simultaneously
with a show of fingers how many of the
four quantities changed (form an O with
fingers if answer is zero). Then we discuss
and fill out each row.
Example 6-1
Which of these quantities change significantly in each situation?
SITUATION
object is
crushed
object taken to
the moon
object tossed
upward
half of object is
destroyed
MASS
WEIGHT
VOLUME
DENSITY
no Δ
no Δ
decreases
decreases
no Δ
decreases
no Δ
no Δ
no Δ
no Δ
no Δ
no Δ
decreases
decreases
decreases
no Δ
Unit 6: A Property of Matter (Mass)
Meador’s Inquiry Physics
On Earth, 1 kg weighs 9.8 newtons:
2
9.8 N = (1 kg)(?)  insert 9.8 m/s to balance it
Page 3 of 4
I put a large newton dial spring scale on
the board (using a magnet or hook) and
hang a 1 kg mass on it to show them it
weighs 9.8 N.
so
(weight equals mass times the acceleration due to gravity)
and the newton is thus equal to a kgm/s2
Conversions
1 pound (lbs) = 4.4482 N
1 kg = 0.068522 slugs
weight is not mass, so it is NOT appropriate to convert kg to N or lbs; instead we use Fg = mg
Example 6-2 MY WEIGHT AND MASS
I use my own weight in
example 6-2, asking them to
calculate each line with me,
but using their own weight. I
use a different color marker
for all of the numbers that
will be different in their own
notes.
I weigh __170___ pounds.
So I weigh
My mass is
or my mass is
“g” is the “acceleration due to gravity” in m/s2 or can be
called the “gravitational field strength” in N/kg instead
, and it varies with location.
I use the PowerPoint in the
“acrobat/Other Resources”
subdirectory on the CD-ROM
to illustrate gravity
variations due to location and
the effects of special
relativity.
Example 6-3 GRAVITY VARIATIONS
Location
g
My Weight There
Chicago
9.803 m/s2
Fg = mg = (77.2 kg)(9.803 m/s2) = 756.79 N / 4.4482 N/lb = 170. lbs
Panama Canal
9.782 m/s2
Fg = mg = (77.2 kg)(9.782 m/s2) = 755.17 N / 4.4482 N/lb = 170. lbs
North Pole
9.832 m/s2
Fg = mg = (77.2 kg)(9.832 m/s2) = 759.03 N / 4.4482 N/lb = 171 lbs
Space Station
8.71 m/s2
Fg = mg = (77.2 kg)(8.71 m/s2) = 672.41 N / 4.44822 N/lb = 151 lbs
Moon surface
1.62 m/s2
Fg = mg = (77.2 kg)(1.62 m/s2) = 125.06 N / 4.44822 N/lb = 28.1 lb
Unit 6: A Property of Matter (Mass)
Meador’s Inquiry Physics
Page 4 of 4
Special Relativity
Mass itself varies with speed. Einstein’s Special Theory of Relativity predicts a number of odd
changes as an object approaches light speed, and these effects have been experimentally
confirmed:



mass increases (the inertia of the object increases; it does not have any more electrons,
protons, or neutrons but instead they simply become harder to accelerate)
objects shrink in the direction of their relative motion
time slows down
According to this theory
where v = speed relative to the observer and
c = speed of light = 186,000 miles/second = 3.00x108 m/s
Since c is so large relative to v, this effect is only important at immense speeds; even at half the
speed of light the mass only increases by 16%.
If you want details:
Speed
0
Concorde (mach 2; 1354 mph; 605 m/s)
Voyager Probe (37240 mph; 16648 m/s)
one-half light speed
three-quarters light speed
99% of light speed
light speed (“warp one” in Star Trek)
% of mass increase
0
0.0000000002%
0.000000154%
16%
51%
600%
infinite; matter cannot achieve light speed ("warp one")
and a similar formula applies to time dilation (time slowing down; confirmed by flying atomic clocks
aboard commercial planes and also around Chesapeake Bay; the clocks in the air slowed down just as the
theory predicted, falling out of sync with clocks left on the ground)
I like to show my students about 8 minutes from a funny 1957 film by Dr. Irwin Moon, The Mystery of Time,
which you might be able to to get from http://www.archive.org, but be aware that Dr. Moon had a religious
motive and was covering more than special relativity; we only watch 16:42-23:00 of that video.
I refer students wanting more details to their textbook and for those who are really motivated, I’ll loan
them a copy of Martin Gardner’s excellent book, Relativity Simply Explained (formerly titled Relativity for
the Million).
Next I show them fun online clips from NASA’s old Vomit Comet zero-g
simulator plane and some excerpts on the effects of freefall on the human
body from the 1994 video We’re Go for Launch to Zero-G.
Then I assign the reading, the worksheet on the Vomit Comet, and we do
6 Lab B. We capture the big idea from 6 Lab B in the Unit 7 notes.