SpaceShipOne ???

snipped-for-privacy@mindspring.com (bert harless) wrote on 25.06.04 in :

Actually, it *is* the same; you *are* in orbit when you can float M&Ms. That's what makes it work. It's just that that orbit isn't approximately circular, it's a rather narrow ellipsis, and it intersects the surface of the earth so you can't just stay in that orbit (one way or another). If you throw a rock, that rock is pretty much in orbit as well (neglecting air drag here) until it impacts somewhere. It just looks like a parable, it actually is the tip of an ellipsis ... the other tip being far down in the earth, at the other side of the core from where you are.

Kai

The radial or centripetal force on an object in orbit is gravity. It is what causes the constant acceleration, bending the trajectory into a circle. All orbits are actually elliptical - circular orbits are just a special case with eccentricity = 0.

Brad Hitch

Well, of course. But in talking "free fall", gravitational acceleration, uniform circular motion, and orbits, it is necessary to differentiate between centripetal acceleration and gravitational acceleration. Centripetal acceleration requirements for "orbital" motions exist independent of gravity. Gravity just supplies the force to maintain the required centripetal acceleration for satellites in Earth orbit.