| |
This lesson concludes the basic skills you will need to succeed
in physical science. The topics covered are DENSITY, SCIENTIFIC
METHOD, PROPERTIES OF MATTER, and MASS vs. WEIGHT.
DENSITY
Will it sink or float? Is it pure gold or gold-plated
lead? Determining an object's density can answer such questions
as these. Density is defined as the ratio
of mass to volume or how tightly packed the atoms
are in a given space (volume). The equation we use to calculate
density is: D = m / V (or m
= D x V or V = m / D; m= mass in grams, V= volume in
ml or cc's). The atoms themselves can also vary greatly in mass
without a significant change in volume since they are mostly
empty space with the nucleus containing most of the matter. This
means that equal volumes of gold and silver can have the same number
of atoms but the gold will have twice the mass because its nucleus
has twice the protons and neutrons.
Space between individual atoms (and molecules) can also vary and
affect the density. The atoms are slower and closest together
(most dense) when they are in the solid state and farthest apart
and faster when they are in the gaseous state.
Kilograms/Liter (Kg/L) and grams/milliliter (g/ml)
or grams/cubic centimeter (gm/cc) are the most common
metric units of density. Here are some densities (g/ml) of common
substances:
| Water 1 |
Air .001 |
Wood .5 -.8 |
Oil .9 |
| Lead 11.35 |
Zinc 7.113 |
Iron 7.894 |
Nickle 8.902 |
| Gold 19.32 |
Silver 10.5 |
Copper 8.96 |
Mercury 13.546 |
So, how much volume (mL) would 50 grams of Nickle occupy?
( ans: V = m / D or V = 50 / 8.902 or 5.617 )
The Scientific Method
Science is best defined as a careful, disciplined,
logical search for knowledge about any and all aspects of the universe,
obtained by examination of the best available evidence and always
subject to correction and improvement upon discovery of better evidence.
What's left is magic. And it doesn't work. -- James Randi
It is a capital mistake to theorize before
one has data. Insensibly one begins to twist facts to suit theories,
instead of theories to suit facts. -Sir Arthur Conan Doyle
The scientific method is a logical approach to
solving a problem.
The steps of the scientific method are:
a) Stating the problem
b) Gathering data through observation, experimentation, and research
c) Forming a hypothesis (possible solution based on data)
d) Testing the hypothesis
e) Conclusion
Suppose you built a water
rocket and wanted to launch it so that it would travel
the farthest horizontal distance. You suspect several possible
factors might contribute to this desired effect, i.e. pressure,
amount of water, wind speed and direction, mass of rocket, aerodynamic
shape, and launch angle. You decide to not complicate your experiment
so you only test one factor (launch angle) at a time, keeping
all other factors constant. You choose a calm day, fill the rocket
exactly half full with water, pump it with exactly 60 psi of pressure
and launch it from the exact spot at a variety of differnt angles.
You are smart enough to avoid zero and 90 degree launch angles,
figuring neither will get you very far horizontally. You carefully
measure the distance with a metric tape and record your angle
vs. distance data, noticing that the farthest distances are in
the 40 - 50 degree range. Further launches and smaller steps show
the best angle to be 45 degrees, half way between horizontal and
vertical. You hypothesize that 45 degrees is the best launch
angle based on your data and observations but strongly
suspect that the amount of water (rocket fuel) is also important.
Locking the launch pad at 45 degrees you now begin to vary the
amount of water and something unexpected occurs. More than half
water makes the rocket fly a shorter distance and less than half
water makes it fly even farther! You conclude that a launch angle
of 45 degrees is important but not the only contributing factor
and decide to plan further individualized testing of water amount,
pressure, mass of rocket, and aerodynamic shape.
Properties of Matter
The two kinds of changes that occur in matter are physical
and chemical. In a physical change, no new substance is formed.
However, physical properties such as size, color, hardness,
density (mass, volume), shape or phase (solid, liquid, gas) may
change. In a chemical change, one or more new substances
with new and different properties are formed. Flammability
(burning), reactivity with acids, bases, or water (rusting of iron),
are examples of chemical changes.
Mass vs. Weight
The concepts of mass and weight seem virtually identical but there
is a difference. Take a 30 kg rock to the moon and imagine what
characteristics about the rock have changed. It hasn't lost any
of its matter so it still has a mass of 30 kg. But things weigh
less on the moon, 1/6th its earth weight in fact. Weight is due
to the force of gravity which varies from planet to planet and
even varies slightly with changes in altitude (farther from the
center of the earth). The metric weight unit is the Newton (N).
1 kilogram = 9.8 Newtons (neglecting friction, all matter
accelerates toward earth at 9.8 meters/sec/sec). On the moon
1 kilogram = 1.6333 Newtons. So, our 30 kg rock would weigh
294 Newtons on the earth (30 x 9.8) and 49 Newtons on the moon (30
x 1.6333).
|
|
