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Name: _KEY_________________________________________________Date: ___________ Period: ____________ 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!