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

*From*: Ablang <HilaryDuffEverAfter@xxxxxxxxxxxxxxx>*Date*: Tue, 19 Apr 2005 23:28:36 -0700

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

.

**Follow-Ups**:**Re: how does lb ft ft / sec sec -> kwh ?***From:*tadchem

**Re: how does lb ft ft / sec sec -> kwh ?***From:*bz

**Re: how does lb ft ft / sec sec -> kwh ?***From:*CWatters

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