Ok, I'm back with a first try. Keep in mind that this is my first try, I reserve the right to change what I said, or the way I said it.

Originally Posted By: Bill S.
It might be argued that it is unlikely that a consistent push, or pull, in one direction will result in motion in a direction at an angle of 90 degrees; but this is exactly the situation in the case of one body orbiting another, larger body. If we reason that the moon is attempting to travel in a straight line past the Earth, but because of the gravitational attraction between them it is being constrained to orbit the Earth, then it follows that the line of force holding the moon in its orbit lies perpendicular to the direction in which the moon is travelling.


That is the way it is. I think you are thinking about what happens when you push against something you can't move. In that case it feels a lot like you are doing work. In a way you are, but the work is internal to your body. There is no energy exchange between your body and what you are pushing against, so the work function is equal to zero. Anytime a force is applied to something, but that force does not produce motion in the something then there is no work performed. In physics work only occurs if it causes a change in motion of the object to which a force is applied. Now then you might say that because the moon is in orbit the gravitational force causes the moon out of a straight line, so so work has been done. To answer that I unfortunately had to think some more. The result is the following.

First off, energy and work are basically the same thing. They use the same unit the Joule = 1 Newton Meter.

I will assume that the moon has a circular orbit for simplicity. The amount of energy imparted to the moon to move it out of a straight path in any infinitely small increment in the orbit is f F*D*cos(dtheta). That is dW/d(theta) = Wd*cos(dtheta). If we integrate over theta from 0 to 2pi then the result is that W = 0. So there is no work involved in holding the moon in orbit. And I hope that I got that right. I haven't done any calculus in many uears. I did just run through the calculus list on Khan Academy, but that doesn't make me perfect by a long shot. Maybe somebody on here knows more than I do and will correct any errors. I am pretty sure that the result is correct, but I may have made some error in how I did it.

Bill Gill

C is not the speed of light in a vacuum.
C is the universal speed limit.