Why did Schumaker comet break up before impact since it was in free fall and according to Einstein should feel no force?

Answer 1

The Shumaker-Levy comet wasn't necessarily in a free-fall. Although free fall can be described as an object that is falling under the influence of gravity, in reality, you can think of a free fall as a an object with a constant drop but doesn't actually fall. As an example, when the space shuttle is orbiting the earth, the astronauts (and the shuttle for that matter) are all weightless becasue they are in a free fall. However, their relative inertial motion (at a perpendicular angle) to the earth with the proper speed (about 17,500 MPH) keeps them in a constant free fall. That is they are falling, but because the earth keeps falling away from them, they never actually fall.

The Shumaker-Levy comet was not in a free fall and was atracted to Jupiter buy it's gravity and was exposed to tidal forces. A tidal force is the gravitational pull between two objects. The closest side of the object to another gravitational force is subject to a greater force than the opposite side (the side furthest away). As Jupiter was also spinning on it's axis, it's pull on the comet in conjuction with the comets gravitational pull, caused it to break up.

Einstein was comparing the force that a body feels during free fall is the same as a body feels when the force of gravity is equal between two bodies. For instance, an astronaut orbiting the earth in the shuttle feels weighless because he (or she) is in free fall. An astronaut in a space capsule on the way to the moon will also feel weigtless. At the halfway point, when the moons gravitational pull equals that of earth, the gravitational pull balances out. Neither astronaut can tell whether they are in free fall or in a zero balance gravitational pull. The effect is excatly the same.

Once an object passes through the Roche limit, which is when a celestial body, held together by its own gravity will disintegrate due to a second body's tidal forces and the gravitational force of the second body exceeds the first object's gravitational self-attraction. This is what happened to the Shumaker-Levy comet.

I tried to make the explanation as simple as I could. I hope I didn't confuse you more.