Download psc 1121 – physical science

PSC 1121 – PHYSICAL SCIENCE
“Physics through Music”
EQUATIONS PROVIDED IN FINAL EXAMINATION
NOTE
There is a good chance that some previous exam questions will be repeated. Study the old exams
and be sure you know the answers to questions that you missed.
Some Numbers
1 m=3.28ft
1 mi=1.6 km =5280 ft
1 N=0.225 lb
1 atm=14.7 lb/in2
g=9.8 m/s2=32 ft/s2
You must know what these equations refer to and what they mean. You may be expected to know
other relationships as well. It is your responsibility to figure out what may be missing here that is
nevertheless very important.
The start of the semester concentrated on some fundamentals of the mechanics of motion.
We discussed distance (d) and time (t) and found that d=vt. The “v” was the velocity and was
defined as the change in distance per unit time. We then defined acceleration (a) as the change in
velocity per unit time. This left us with equations such as:
v=(xf-xi)/2; a=(vf-vi)/2
d=vt
v=v0 + at.
Average speed was (vf-vi)/2.
d=(1/2) at2
We found that things in “free-fall” fall with the acceleration of gravity, g, which is equal to 9.8
m/s2 or 32 ft/s2. The above equations hold. So when you drop something, you should be able to
figure out how long it takes to fall to the ground and how fast it will be going when it hits the
ground.
We introduced the concept of Forces and then discussed the three Newton Laws that you should
be able to quote. For the second law, we used
F=ma
to calculate F or a when one of them was supplies along with the mass.
We defined momentum (mv) which we found was conserved during collisions so that the initial
mv was equal to the final (after collision) momentum. mv is the TOTAL momentum of all of the
objects you are working with. During collisions, we defined the impulse (force x time) and found
that this was the change in momentum that took place during the collision. We applied this to the
concept of pressure.
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Speaking about pressure, p,
p=force/unit area.
Period of an Oscillator = time per oscillation
Frequency of an oscillator = number of oscillations per second
f=1/T or fT=1
For a spring, the force F is given by
F=-kx
The period of an oscillating mass at the end of a sprig, f , is given by
f 
1
2
k
m
ENERGY: Work is a force times the distance through which the force acted:
Work = Force x Distance
momentum = mv
momentum is “conserved” in a collision (know what that means)
If something hits a wall and bounces back, the wall applies a Force over a period of time that
changes the momentum of the particle. Momentum is ONLY conserved when there are no
external forces. So,
F t = change of momentum = 2 x initial momentum
The kinetic energy of an object is
KE = (1/2) mv2
and we then decided that ENERGY IS CONCERVED, meaning that the total energy before a
collision is equal to the total energy after the collision. Consequently sound from a crash takes
some energy away from the total. We call this noise, but if a drum stick hits a drum, it becomes
something related to music.
We then LIFTED an object from an initial reference level to a final level and called the energy
POTENTIAL energy. Based upon the definition of how much work is done on an object when it
is lifted through a height h, we defined the PE as:
PE = mgh
and PE counts in the energy conservation equation!
So the energy before a collision of an object (KE + PE) = total amount of energy available after
the collision (KE + PE + losses due to heat, friction, sound, etc.)
The potential energy of a SPRING was found to be
PotentialEnergy spring  PE spring 
1 2
kx
2
2
The period of a pendulum was also mentioned:
T  2
l
g
WAVES:
Velocity of a wave on a string =
tension
mass / unit  length
Most of the musical ideas did not require equations but those that did should be remembered.
(Nodes, etc, leading to wavelengths of a sound).
After a while, we went to some concepts of electricity. For a simple circuit, after we discussed
charge (coulombs), we reviewed the following:
Capacity=Charge/Volt or Q=CV
We define resistance and current.
I=current=charge/unit time.
Resistance and current were related by:
V=IR
V was the work per unit charge necessary to move a charge from one point to another.
We then went back to the concept of power.
Power=Work per unit time = W/t
P=i2R=IV in a circuit.
For sound/music, we defined intensity I = Power/unit area. We figured out what the intensity was
a distance from a sound source. The intensity was reduced as the square of the distance from the
source.
We discussed reverberation time (what is it?) and the factors that control it.
If I missed any “formulas” that you should have (rather than know), I will provide them at the
exam.
The best review is the PowerPoint presentations, which are on the website.
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