Download Think/Explain Gravity

1. If you stood atop a ladder that was so tall that
you were twice as far from the earth’s center as
you are now, how would your weight compare to
its present value?
7. If the gravitational forces of the sun on the
planets suddenly disappeared, in what kind of paths
would they move?
2. The planet Jupiter is more than 300 times as
massive as earth, so it might seem that an object
on the surface of Jupiter would weigh 300 times
as much as on earth. But it so happens that an
object would scarcely weigh three times as much
on the surface of Jupiter as it would on the
surface of the earth. How can you explain this?
8. By what factor would your weight change if the
earth were twice as big and had twice the mass?
3. If the earth somehow shrunk to half size
without any change in its mass, what would be
the value of g at the new surface? What would be
the value of g above the new surface at a distance
equal to the present radius?
9. A black hole is no more massive than the star
from which it collapsed. Why then is gravitation so
intense near a black hole?
4. A friend proposes an idea for launching space
probes that consists of boring a hole completely
through the earth. Your friend reasons that a
probe dropped into such a hole would accelerate
all the way through and shoot like a projectile out
the other side. Defend or oppose the reasoning
of your friend.
10. The weight of an apple near the surface of the
earth is 1 N. What is the weight of the earth in the
gravitational field of the apple?
5. If you stopped an earth satellite dead in its
tracks, it would simply crash into the earth. Why,
then, don’t the communication satellites that
“hover motionless” above the same spot on earth
simply crash into the earth?
11. Evidence indicates that the present expansion of
the universe is speeding up. Is this consistent with,
or contrary to, the law of gravity? Explain.
12. If you stand on a shrinking planet, so that in
6. If the moon were twice as massive, would the
effect you get closer to its center, your weight
attractive force of the earth on the moon be twice
increases. But if you instead burrow into the planet
as large? What about the force of the moon on
and get closer to its center, your weight decreases.
the earth?
Explain.