By Dale D. Long

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Die Abenteuer des Jonathan Gullible - Eine marktwirtschaftliche Odyssee

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Conversazioni in Galiziano La routine quotidiana in Galiziano

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Extra resources for The Physics Around You

Example text

For escape velocity, and setting this velocity to c, mass, its rs in the expression we see that the sun would become a black hole if it were shrunk to a diameter of 6 km. The earth would be a black hole if it were about 2 cm in diameter instead of 13,000 km. Since the escape velocity at the Schwartzschild radius equals the speed of light, nothing, not even light, can escape the strong gravity and, for this reason, about what we the object a black hole. , matter, make up the matter). Actually two more pieces of information about the black hole that we can know; these are its electrical charge (Chapter 14) and its angular momentum (Chapter 6).

The mass of an same on the chair. The up on your body. You can be sure of this because, if the chair were not there, you would fall to the floor. The force with which the chair pushes on you is exactly equal to the force with which you push on the chair. The force from the chair, however, is applied in the opposite direction of the force from your body (Fig. 6). When you hit a tennis ball with a racket, the racket exerts a force on the ball. The ball exerts a force of the same strength on the racket, but in the opposite direction.

Real interest in black holes was generally lacking, however, until the late 1960s when astronomical observations of pulsars (rotating neutron stars) showed that black holes might indeed exist in nature and not just in our theoretical constructs. Perhaps the easiest way to imagine a black hole is to consider (as the velocity one body needs to escape Laplace did) the escape velocity, v t from the gravitational field of another. Newtonian physics shows that — for a spherical planet of mass m and radius r, ve = V2 Gm/r, where G the universal gravitational constant.