how does lb ft ft / sec sec -> kwh ?



4/6/01

How does the English units of potential energy (PE) or kinetic energy
(KE) relate to that of energy (E)?
In equation terms, how does:

lb ft ft / sec sec -> kwh

--

Horsepower? Course, HP is power -- energy/time, as is KWs:
1 HP = 550 ft lb/sec
1 HP = .7457 KW
1 KW = 737.6 ft lb/sec

'Member, it's easy to confuse energy and power. Gotta get yer units
right. BTUs (ft lb) & Joules (kg calories) are the relevant energy
terms for English & metric.

Ach, I dinna answer yer question completely -- I forget what the
proper "class" kinetic energy (mass x velocity x velocity) is. BBA?

P.S. How many Gills/Grain are in a Rod/Rope?

--

Well, the equation for KE is
0.5 * mass * velocity * velocity

I'll have to re-look at what to wrote to see if PE or KE can relate to
energy = power * time (kwh)

--

Why do the units of measure matter? - its just a matter of conversion
from whatever you start with - potential energy and kinetic energy and
work are all one and the same. Even Einstein knew that potential
nuclear energy was mass times the speed of light squared; so the units
of energy are (lb-mass)x miles x miles/(years*years);or work is a
force times a distance (ft-pounds)(wherein the mass is expressed as
pound-force; not pound mass) so you raise that 1 pound mass 10 yards
against the acceleration of gravity at 9.8 feet per second each second
and you end up with lb-mass X yards x feet/(second*seconds). That's
why we should go metric - to eliminate the confusion between pound-
force and lb-mass
courtesy of quattro pro help I cut and listed a bunch of different
units to measure energy by; just remember they are all one and the
same - just a measure of energy and you could go straight to a program
like that and convert one to the other.

Energy measurement units

Energy Unit
Joule "J"
Erg "e"
Thermodynamic calorie "c"
IT calorie "cal"
Electron volt "ev"
Horsepower-hour "hh"
Watt-hour "wh"
Foot-pound "flb"
BTU "btu"

some sample conversions(all below are the same amount of energy- at
least by QuattroPro):

Calories 10
Foot lbs 993.544094443283
Joules 41.8679484613929
hp-hour 1.55960800463137E-05
erg 418679283.372801
btu 0.0396830723907002

Still didn't totally help you with the unit conversions from
watt-hours to foot-lbforce; but you already answered your own
question. Energy is also power times time. so take your power in
Watts; express it metric units as a watt=1 joule/sec; so a watt*sec is
non other than a joule; which is the amount of energy an object of 1
kg mass gets when you raise it one meter against a newton of force
cause by gravity at the earths surface. I can't do this in English
units.

--

Kinetic energy is energy due to relative motion.
Mechanical energy is the ( very important term here...) 'algebraic
sum' of potential energy and kinetic energy. ( That means you take
vectors into consideration, which is vector algebra with complex
numbers and all, lol ).

Basics:

Energy= The ability to do work or produce an effect.

Internal energy, Kinetic energy and Potential energy are forms of
STORED energy.

HEAT and WORK are two forms of transient energy.

WORK is the transfer of energy from one object to another due to
actions of a force acting on an object through a displacement (
phew...)

Power is the rate at which Work is done.


quote:
--------------------------------------------------------------------------------

Why do the units of measure matter? - its just a matter of conversion
from whatever you start with - potential energy and kinetic energy and
work are all one and the same.

--------------------------------------------------------------------------------

Refer to the above in reference to work...

Uh-Oh...Now you got me started...get out the calculators kiddies...

Here is where the units matter...

Say we have an airplane flying at an altitude of 1500 Ft. and a
velocity of 180MPH East The mass of the plane and cargo is 1350
LbM...that means Pounds mass, which only equals pounds force in our
gravity of 32 Ft/(sec*Sec). ( one of these days I'll figure out how to
use the squared ASCII character too )

What is the planes Kinetic Energy?

Eq: KE=(mass)(Velocity*Velocity)/(2)(gravitational constant of
accelleration or 'Gc' )

( The gravitational constant of acceleration for earth is 32 Lbm-Ft/(
Sec*Sec)(Lbf) )

So, we need Velocity in units of measure in Ft/Sec...so unit
conversions gives this:

Speed= (180mi/Hr)(5280Ft/Mi)(1Hr/3600 Sec)

Cancel units and do the math and we get:

= 264 Ft/sec

Now, The KE= (1350
Lbm)[(264Ft)(264Ft)/(Sec)(sec)]/(2)[(32Lbm)(Ft)/(Lbf)(Sec)(sec)=

1470150 Ft-Lbf ( foot pounds force )

The Potential energy is:

PE=(mass)(gravitational accel)(displacement in terms of 'height')/Gc

PE= [(1350 Lbm)(32Ft/Sec*Sec)(1500 Ft)]/32 Lbm-Ft/[(Lbf)(Sec*Sec)]

Cancel the units and do the math and the PE=
2025000 Ft-Lbf

The total mechanical energy is given as :
ME=PE+KE

-or-

1470150 Ft-Lbf + 2025000 Ft-Lbf = 3495150 Ft-Lbf

So, as you can see...physics is IMPOSSIBLE without UNITS.

If we were to carry this further and see what effect the plance could
have on another object in motion, the vectors would be extremely
important, then the math gets complicated...so I'm not even gonna
attempt to calculate the outcome of the energy of a mid air colliosion
here, AKA: Chineese fighter Vs recon plane...lol.



===
"For the things we have to learn before we can do them, we learn by doing them."
-- Aristotle
.



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