Ditto Tobin wrt Warren's comment, plus this:

Kinetic energy of a one ton car at 60 mph (relative to the road surface):

1 short English ton ~ 907 kg.
60 mph ~ 26.7 m/sec

Newton = kg-m/sec^2, a unit of force (mass times acceleration)

Joule = kg-(m/sec)^2 = N-m, a unit of work (force times distance) or energy (mass times velocity squared)

Watt = Joule/s, a unit of power (energy over time)

So I make it 647 Kilojoules, give or take.

According to James Watt (who extrapolated for data from ponies, sez the ever-unreliable Wikipedia), a horse can sustain an energy output of mechanical work (e.g. turning a millstone) at the rate of 746 Watts, i.e. can keep 7 light bulbs lit for several hours. Supposedly a real horse pulling real hard can produce more like 11 Kilowatts over a shorter period of time.

If our car hits something and suddenly comes to rest (wrt the road surface), 647 Kilojoules is the amount of energy it must expend, in a hurry. So if it stops in a tenth of a second, you could say that the car very briefly produces (on average) an impressive 6 Megawatts. (Unfortunately, this energy is mostly wasted in crumpling the car and the barrier, so it cannot be used to keep 1667 lightbulbs lit for one hour.)

For comparison, a modern railroad locomotive sustainably produces about 6 Megawatts while hauling a heavy train. This power is converted (I guess) into waste heat (via friction with the rails) and local atomospheric turbulence (the engine must push air out of its path, and then there is aerodynamic drag).

http://en.wikipedia.org/wiki/Orders_of_magnitude_(speed)
See
http://en.wikipedia.org/w/index.php?...oldid=16259988
for conversions to geometric units, in which

• angular momentum is measured in units of area,
• mass, energy, and time are all measured in units of length,
• velocity is dimensionless,
• acceleration is measured in units of 1/length (units of path curvature) ,
• energy density, momentum density, and pressure are measured in units of 1/area (units of sectional curvature)

Something I learned from Isaac Asimov: most of the 100 Watts required to operate a lightbulb goes into radiant heat, not visible light. A living human also produces about 100 Watts of waste heat. That's why cramming them into black holes makes 'em testy.

Exercise: get some incandescent lightbulbs (not the Mercury vapor kind!) and drop them from 0.5-2m to determine the average height required to break them. Use your knowledge of Newtonian physics to deduce the energy required to break a lightbulb. Compare with the energy required to keep one lit for six hours. Ponder the ease of destruction versus doing useful work. Then spend some time with ATM, the only place I know where destruction counts as useful work ;-/

Exercise (for those who know how to compute the Newtonian gravitional binding energy of the Sun): what would be the Newtonian energy required to spaghettify the Sun? (That is, radially compress orthogonal to some axis of axial symmetry while simultaneously elongating twice as fast along the axis of symmetry, which changes the surface from a sphere to a prolate spheroid while keeping the volume constant.)

__________________
Chris Hillman

Read these PF posts. Avoid Wikipedia--- except for these versions. Read this and this suggested sticky. When asked for advice, I always say: never take advice!