MadSci Network: Astronomy

Re: What would happen if nothing had gravity?

Date: Fri Dec 8 17:58:17 2006
Posted By: Michael Maskell, Grad student, Physics, Old Dominion University
Area of science: Astronomy
ID: 1141775628.As

Well, if nothing had ever had gravity, the universe would have developed in
a completely different way from what we see now, and life as we know it
would not exist.

Let's think, then, about what would happen if gravity just suddenly
disappeared all at once today.  To think about that, let's think about what
gravity does in our solar system.  You probably know that the planets orbit
around the sun.  This orbit is caused by gravity.  The planets are
constantly trying to fly off in a straight path, but the sun's gravity
pulls them into a curved path around it.  Look at the picture here,
which is obtained from this Web page.

It shows a planet orbiting the sun.  Its "instantaneous velocity"
is the speed and direction it's moving at when you take a snapshot of the
solar system.  You can see that this velocity points in a straight line
from the edge of the circle.  This kind of line is called a "tangent" of
the circle.  The "centripetal acceleration" in the picture is the
acceleration caused by gravity pulling the planet inward.  You can then see
that this inward pull results in the "resultant orbital path" taking the
planet around the sun.  If gravity disappeared, that centripetal
acceleration would disappear also, and the planet would fly off along
whatever tangent its instantaneous velocity was pointing on when gravity

So if all of a sudden nothing had gravity, the solar system would fly apart
as the planets all went off in straight lines from their orbits.

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