Download Thinking About Gravity

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Thinking About Gravity
Part 1 - Go to the following website:
http://phet.colorado.edu/en/simulation/gravity-force-lab and use the “Gravity
Force Simulation” to explore the variables that affect gravity. Record your
observations below.
Identify two factors that can change the amount of force (gravity) the objects
experience.
1. Mass
2. Distance
Complete the chart for each scenario below.
Mass
Distance
Mass
of 1
of 1
of 2
Distance Force on m1 by
of 2
Force on m2 by
m2
m1
25 kg
0m
25 kg
8m
0.000000000650 0.000000000650
25 kg
2m
25 kg
5m
0.000000004763 0.000000004763
50 kg
0m
50 kg
8m
0.000000002608 0.000000002608
50 kg
0m
50 kg
5m
0.000000006846 0.000000006846
3. The force of gravity increases as objects move closer together.
4. The force of gravity increases as an object’s mass increases.
5. Based on what you’ve seen how would you define gravity?
Gravity is a force of attraction between objects based on their mass and their
distance apart.
Part 2 - Watch the following video: https://www.youtube.com/watch?v=lY3XV_GGV0M then
answer the questions below.
6. The law of gravity states that everything is attracted to everything else!
7. How does the mass of an object affect its gravitational pull?
The more mass an object has, the greater its gravitational pull.
8. When two objects of different masses are pulled towards each other, which will move
further?
The object with less mass will move farther than the object with more mass. The
larger object will attract the smaller object towards it more strongly.
9. How does the distance of two objects from each other affect the gravitational pull?
The greater the distance between two objects, the lower the gravitational pull
between them. When two objects are closer to each other, there is greater
gravitational pull between them.
10. How is does gravity behave like magnetism?
Larger magnets attract things towards them more strongly, and the closer two
magnets are to each other, the more strongly they are attracted to one another.
Gravity acts similarly because more massive objects have more gravity and therefore,
they attract objects to them more strongly, and the closer two objects are to each
other, the greater the attraction between them.
Part 3 - Go to the following website: http://phet.colorado.edu/en/simulation/gravity-andorbits and use the “Gravity and orbits Simulation” to explore the variables that affect an
objects orbit. Record your observations below.
11. Select the Sun and Earth. Draw the path of the Earth orbiting the Sun.
12.Select the Earth and Moon. Draw the path of the Moon orbiting the Earth.
13.Based on your observations, what similarities and differences can you observe about
the motion of the Earth orbiting the Sun and the motion of the Moon orbiting the Earth?
Similarities:
They both have an elliptical orbit, they both orbit at a constant speed.
Differences:
The moon is much closer to the Earth than the Earth is to the Sun, The Earth’s
orbit around the Sun takes much longer than the moon’s orbit around the Earth
14.Select the Sun, Earth and Moon. Explore the simulation to determine what keeps the
Earth in orbit around the Sun and the Moon in orbit around the Earth.
a. What do you think the gravity force arrows represent?
The direction and strength of the force of gravity between two objects.
b. What do you notice about the size of the “Gravity Force” arrows?
The larger the gravity the larger the arrows. The gravity force arrows between
the Earth and the Sun are much larger than those between the Earth and the
Moon, because the Sun and Earth exerts more gravity than the Moon does (they
have more mass).
c. In what direction do the arrows point? What do you think this means?
The direction object are pulled (attracted) toward one another
d. Based on your observations, how does gravity affect the Earth’s orbit around the
Sun and the Moon’s orbit around Earth? The Sun’s gravity keeps the Earth in
orbit around it, it pulls the earth inward as inertia causes it to move forward.
The earth’s gravity keeps the moon in orbit around it in the same way. Because
the earth is closer to the moon than the Sun is, Earth exerts a stronger force of
gravity on the nearby moon and keeps it in orbit.
15. Hypothesize:
a. If the Sun was less massive, but still the same distance from Earth, what do you
think would happen to our Earth’s orbit?
b. If the Earth were much more massive than it is, but still the same distance from
the Sun, what do you think would happen to earth’s orbit?
c. If the Sun and Earth were their current sizes, but four times as far apart, what do
you think would happen to the Earth’s orbit?
It takes 365 days for the Earth to complete one revolution (orbit) around the Sun. Find three
different ways to change the number of days it takes for the Earth to complete one revolution
around the Sun.
Method What did you
What happened How many days Observations
do?
to the
did it take to
gravitational
complete one
force arrows?
revolution?
Made the Sun
Larger
They were
longer
150 days
Made the Earth
larger
They were
longer
375 days
Moved the Sun They were
and Earth closer longer
together
135 days
1
2
3
The Earth’s orbit was much
more elliptical, the
revolutionary period was
shorter, the Earth sped up
closer to the Sun and slowed
down when it was further
The Earth’s orbit was more
circular, and slower
The Earth’s orbit was more
elliptical and the
revolutionary period was
shorter
16. In a few sentences, what can you conclude about how the size of a planet and its
distance from the Sun affects its orbit?
The larger the Star is the more gravitational force it will exert, pulling planets towards
it, the planets will orbit more quickly and be pulled more strongly giving a more
elliptical orbit. When the planet is larger it will orbit the star more slowly. The closer a
planet is to its star the more quickly it will orbit, further away from the star the
planets will have longer orbits due to the lessened force of gravity.
17. Venus is called Earth’s “sister planet” because it is almost the same size (mass and
diameter) as Earth. Venus is closer to the Sun, what can you say about the following?
(Circle the word you think is correct)
 The Sun has a stronger/weaker gravitational pull on Venus than it does on
Earth.
 Venus has a longer/shorter period of revolution around the Sun when
compared to Earth’s period of revolution around the Sun.
18. Jupiter is has a much larger mass than the Earth and is farther away from the Sun.
What can you say about the following?
 Jupiter has a longer/shorter period of revolution around the Sun when
compared to Earth’s period of revolution around the Sun.
Part 3 - Read the following paragraphs and then answer the questions that follow.
Gravity: Everything has its own gravity. Everything exerts a pulling force on everything else.
However, only large things have enough gravity to successfully pull other objects towards
them. The force of gravity depends on how much mass you have. The larger the object is, the
more gravity it has (The Sun has more gravitational pull than the Earth does). Distance is also a
factor of gravity. No matter how much gravity an object has, if you aren’t close to it, it won’t
pull you in. For example, a black hole is one pinpoint in space with sooooo much mass that its
gravitational pull is sooooo strong even light can’t escape its pull! However, regardless of how
strong its pull is, if you don’t get near it, you won’t be pulled in. In order for gravity to work,
one of the objects needs to have a large mass and the distance between the two objects needs
to be small…makes sense right?
Inertia: Newton’s law says that any moving object will keep moving in a straight line forever
unless something forces it to do otherwise. For example, if we threw a ball out into space, it
would keep flying in the same direction forever unless something crashed into it or it got
caught in the gravity of a planet or star. Newton called this inertia. According to Newton, the
planets are constantly travelling in straight lines away from the Sun. However, while they are
travelling away from the Sun, the Sun’s gravity is constantly pulling them back inwards. This
causes them to appear to circle or “orbit” the Sun.
19. Gravity is a force of attraction between objects based on their mass and their distance
apart. Technically anything with mass has gravity, remember everything attracts
everything else! So why aren’t objects, like your pencil, being pulled towards you?
Explain your reasoning:
They are, however, you and your pencil have such a small mass (compared to objects
like the Sun-Earth-Moon) that it has very little gravity, the Earth’s gravity is much
stronger and will overpower the negligible amount of gravity your pencil exerts, you
would never notice it attracting you or you attracting it.
20.Explain why the Earth orbits the Sun (you must use both the terms gravity and inertia in
your answer).
Earth is an object in motion so according to newton the Earth would keep travelling
forward forever until it runs into another object or is disturbed by an unbalanced
force. The Sun’ gravity provides that unbalanced force. While the Earth is moving
forward due to inertia the Sun’s gravity is pulling Earth in towards it, the simultaneous
forward and inward movement causes the Earth to revolve (orbit) around the Sun!