BruceS wrote:
Mark McIntyre wrote:

"There is a huge force of gravity between the earth and moon - some 70
million trillion pounds (that's 70 with another 18 zeroes after it), or
30,000 trillion tonnes (that's 30 with 15 zeroes)."

Euh, firstly gravity isn't measured in pounds or tonnes

Why would one not use pounds to measure a force?

An old unit of force indeed was Kiloponds (i.e. the force of one
kilogram of mass at normal gravity), which is kind of misleading in
regions that don't have standard gravity, e.g. the earth-moon system.

Anyway, the moon's centripetal force is of course GmM/r^2 and its
binding energy is about -1/2 gmM/r, with r being about 4*10^8 m and GmM
being about 3*10^37 Jm, iaW the moon's binding energy is a few thousend
yottajoules (had to look up that prefix, never used anything bigger then
exa- ).

Lars