E=mc2! E=mc2 stands for energy equals mass times the speed of light squared. I know what the e, the =, the m, and the 2 stand for. I just can't figure out what the c stands for. I get deep in thought when i think about that one letter in this famous old equation.
There are different equations for energy. Kinetic is 1/2mv^2. Potential is mgh. Spring energy is 1/2kx^2
Power in Watts(joules)= current in amps squared x Resistance in ohms.
or
Power in Watts = IxE (current in amps x voltage in volts)
also, 746 watts = 1 hp [horsepower]
Symbol Represents Units
?x, ?y, ?z change in length in x, y or z direction length, meters
A area = xy (or πr
2 if area of a circle) length2, meters2
V volume = xyz (or πr
2l if volume of a cylinder) length3, meters3
v velocity, dx
dt length/time, meters/second
a acceleration (rate of change of velocity,
dv
dt lenght/time2, m/sec2
g acceleration due to earth’s gravity, approximately 9.8 m/sec2 m/sec2
m mass (amount of material) grams or kilograms
F = ma force = mass x acceleration newton (N) = kg m
sec2
weight = mg (mass x acceleration due to earth’s gravity)
Ek
(or KE) kinetic energy = 1/
2
mv2 joule (J) =
kg m2
sec2
Epg (or PE) potential energy due to gravity = mg?z (weight x height) joule (J) =
kg m2
sec2
W = ?(Ek
+ Ep
) mechanical work = change in energy: joule (J) =
kg m2
sec2
W = F?x mechanical work is also equal to force x distance (1 joule = 1 newton x 1 meter)
ET (or TE) thermal energy, a function of an objects mass and its temerpature (see below)
T temperature (?T = T2
-T1
, change in temperature,) °C
Q heat flow (a transfer of thermal energy, from hot to cold) calorie
1 calorie = amount of heat needed to raise the temperture of 1 gram of water 1°C
Q = mc?T heat flow as a consequence of changing an object’s temperature (?T = Q
mc)
c specific heat (heat capacity); for water, c is defined as 1 calorie per gram per °C
W + Q = ?(Ek
+ Ep
+ ET) work done + heat flow = change in energy
P power or rate of energy use: power = work done
time taken =
energy used
time 1 watt = 1 joule
1 second
energy used = power applied x time in use (e.g. kilowatt-hour)Symbol Represents Units
Qc
t
= K?T
?x
A Conductive heat flow
Qc
t
rate of heat flow by conduction 1 watt = 0.239 cal/sec
K thermal conductivity watt per °C per meter
?T
?x
temperature gradient °C/meter
A cross-sectional area through which heat is being conducted meter2
Qr
t
=σεAT4
Radiative heat flow (Stefan-Boltzman Law)
Qr
t
rate of heat flow by radiation 1 watt = 0.239 cal/sec
σ universal constant (fudge factor)
ε emissivity, a property of the material doing the radiation and its surface characteristics
A surface area of the radiator meter2
T4 absolute temperature, raised to the fourth power °K
W = Qhot-Qcold Work done by a “Heat Engine”
from a flow of heat between source (hot or input) and sink (cold or output)
Qin–Qout = W
Qin
Efficiency = useful work done / total energy input
Thot–Tcold
Thot Carnot’s theoretical maximum Heat Engine efficiency (T in °K)
1st Law: Conservation of Energy: input = output + change in storage
2nd Law: Energy Conversion: input = useful output + heat (heat—increase in entropy—must be > 0)
Efficiency = useful work done / total energy input
a consequence of the 2nd law is that Efficiency will always be < 100%
Energy Consumption= intensity of use x level of activity (power x time)
Copyright ? 2001 by Timothy T. Allen
Ask my buddy Albert. Einstein, that is.
