| "E X T R A C R E D I T A S S I G N M E N T" LA-3. DUE DATE MAY 7, 2007.
Name _____________________________ Date ___________________
Gravity
By Sharon Fabian
1.Gravity is not just a force on planet Earth. Each planet has its own
gravity, and each planet's gravity is different. Our moon has gravity too.
So do the moons that circle other planets. The sun has gravity (lots of it).
So do all of the other stars. In fact, everything has some gravity, but only
really big things like planets, moons, and stars, have enough gravity to be
measured.
2.Here on Earth we measure gravity using a scale. Any type of scale will do,
whether it is a triple beam balance in your school's science lab or the
bathroom scale in your house. Your weight is the measure of gravity's pull
on you. Scientists often like to use the word mass instead of weight. For
everyday matters, here on earth, your weight and your mass are the same, but
that is not true everywhere! If you ever become an interplanetary traveler,
you will see that your weight is different on each planet. This is because a
planet's gravity is determined by its own size, or mass. Larger planets have
more gravity; smaller planets have less gravity. This is true for suns and
moons too.
3.Suppose you weigh 100 pounds here on Earth. Would you like to know what
you would weigh in different locations in space? Just look at this
list.
Earth - 100 lbs
Moon - 17 lbs
Mercury - 38 lbs
Jupiter - 236 lbs
Pluto - 7 lbs
the sun - 2407 lbs
a white dwarf - 130,000,000 lbs
a neutron star - 14,000,000,000,000 lbs
in a spaceship far out in space - 0 lbs
4.The force of gravity also depends on how close an object is to the center
of the planet. If you were in a spaceship traveling up through the earth's
atmosphere, the pull of gravity would gradually be less and less, until you
escaped from the pull of gravity altogether.
5.We can see an example of this here on earth too. Scientists who study the
oceans' tides know that tides are caused mainly by the pull of the moon's
gravity, but also, just a little bit, by the pull of the sun. The reason why
the moon's pull is so much stronger is because, even though it is much
smaller than the sun, it is also much, much closer to earth.
6.Gravity is the force that holds moons in their orbit abound their planet,
and planets in their orbit around the sun. Without gravity, moons, planets,
or anything else would just keep going in a straight line. There is a
special name for a force that holds something in a circular path. It is
called centripetal force.
7.Space scientists have found an amazing use for planets' centripetal force.
They have sent up the spacecraft named Cassini to explore the far away
planets. Cassini could never carry enough fuel for its whole mission, so the
scientists planned to have it do a flyby of several planets on its way. As
it zips around each planet, it uses that planet's gravity, or centripetal
force, to pick up speed. Cassini's mission included a flyby of Venus, Earth,
and Jupiter, which all together would pick up as much power as 75 tons of
rocket fuel.
8.The next time someone tells you that gravity is what holds us down on
Earth, you can say that there is a lot more to gravity than that!
1.If you weigh 100 pounds on Earth how much would you weigh on Jupiter?
A.236 lbs
B.100 lbs
C.17 lbs
D.2407 lbs
2.Gravity is measured using a
A.Measuring cup
B.Ruler
C.Scale
D.Speedometer
3.On Mercury, you would weigh
A.More than on Earth
B.Less than on Earth
C.More than an elephant
D.The same as on Earth
4.On a neutron star, you would weigh
A.About as much as a train weighs on earth
B.About as much as an elephant weighs on Earth
C.About the same as on Earth
D.Much more than any of these
5.Tides are mainly caused by
A.The Earth's gravity
B.None of these
C.The sun's gravity
D.The moon's gravity
6.From the information in the article, we can infer that an object's mass
A.Would be more on Jupiter than on Mercury
B.Would be greater on Jupiter than on Earth
C.Would always be the same
D.Would be less on Jupiter than on Earth
7.The force that holds the planets in their orbit around the sun is called
A.Mass
B.Centrifugal force
C.Weight
D.Centripetal force
8.How did scientists use the force of gravity on the Cassini spacecraft
mission?
A.Gravity pulls Cassini back to Earth from outer space.
B.Cassini uses the Earth's gravity to help it blast off.
C.Gravity keeps Cassini from crashing into Jupiter.
D.Cassini gets a power boost from planets' gravity.
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