Gravitv and Orbits Lab 1 GRAVITY AND ORBITS LAB ACTIVITY Student Investigation Date: Name: BACKGROUND A 17th century scientist, Sir Isaac Newton, developed several laws governing the motion of objects, as well as the universal law of gravitation, which explains the motion of planets and many other objects. Newton's first law of motion states that an object will remain at rest, or in uniform motion in a straight line, unless a force acts upon it. He called this tendency for objects to resist any change in motion---inertia. From his observations of the planets, Newton knew that some force must be acting on the planets to pull them towards the sun. He reasoned that this force was the sun's gravity, and that when combined with a planet's inertia, these two factors move the planet into an elliptical, or egg-shaped, orbit around the sun. The amount of time required for a planet to complete one solar orbit is called its period of revolution. Newton's law of universal gravitation states that all objects in the universe attract each other by the force of gravity. Two factors which affect the size of the force are the masses of the objects and the distance between them. The force of gravity increases as the masses of the objects increase, and decreases as the distance between objects increases. As the force of gravity acts on the nine planets orbiting the sun in our solar systen, the factors of mass and distance affect each planet's period of revolution. This same law influences the motion and orbits of other objects, like the moon and artificial satellites launched into space. In this exercise, you'll explore Newton's laws and the principles which govern the effects of gravitational force on orbits. MATERIALS REQUIRED (per student/group) 1 Plastic strip, 1" x 13" See instructor for the following: 1 Steel ball, 1/2" 1 Styrofoam ball, 3" * Sheet of white paper, 8 1/2" x 11" 1 Length of plastic tubing, 3/16" x 6" * Marking pen 1 Plastic tube with cap, 1" x 5" * Transparent tape 1 Length of nylon line, 36" * White glue - 1 Screw eye * Safety goggles 25 Washers, 1" 0.D. x 7/16" LD. * Stopwatch or timer 1 Set of student copymasters Gravity and OrbitsLab 2 Name: Date: PROCEDURE (Part I) In Part I of this activity, you will be constructing a simple model to investigate the effect of gravity on a moving object. A. Locate the 1" x 13" strip of flexible plastic and bend it into a hoop shape. Overlap the ends about 1/2", and tape the ends securely together with transparent tape to form your hoop. B. Place the hoop in the center of a sheet of white paper, and draw a circle onto the paper around the outer edge of the hoop. Mark four points at equal distances around the circle and number each one: 1 through 4 (see illustration). C. Now place a steel ball inside the plastic hoop as it rests on the paper. Slowly rotate the hoop clockwise until the ball rolls smoothly . around the inside edge of the hoop. When you have established a steady motion, stop Ball swirling the hoop as the ball approaches 1 7 point #1 on your paper, then quickly lift the hoop to allow the ball to escape. This procedure may take some practice, so try it a few times until you are comfortable with O ||y 4 e the release of the ball. D. Observe and record the path of the steel ball \\ as it exits the hoop at point #1. Repeat Steps C & D, but stop the hoop and release the ball at points 2, 3, and 4. Answer the questions which follow. s QUESTIONS (Part I) 1. How would you describe the path the steel ball takes when it exits the hoop? Is it the same for all 4 exit points? - It moves in a straight line tangent to the hoop. 2. Asthe steel ball travels within the hoop, in what direction does the hoop push the ball? Gravity and OrbitsLab 3 Name: Date: 3. If we compare this model to an orbiting planet, what force does the hoop represent in changing the motion of the ball? 4. How would you compare the motion and forces at work on the s;eel ball with those of a satellite orbiting the earth? How are they alike? How are they different? PROCEDURE (Part II) In this exercise, you will construct a model to explore the relationshi;? bet_ween gravitationial force and the period of revolution of an object in orbit. Follow all safety du_'ectxons when operating your model, and work in pairs or small groups to make your observations. A. Obtain the pre-assembled gravitational model from your instructor, or assemble the unit by following your instructor's directions. B. With the model assembled as shown in Figure 1, place 5 washers in the plastic tube suspended from the nylon line. Try to drop the washers in so that they lay flat at the bottom of the tube as shown. Nylon line FIGURE 1 / Styrofoam ball s 3/16" tubing Screw eye Plastic tube Washers Gravity and OrbitsLab 4 ravity and Orbits Lab 5 Name: Date: Name: Date: C. Check your setup to make sure that the nylon line is securely connected to the ball and " to the plastic tube with washers. Holding the 3/16" x 6" length of plastic tubing in one 7. Compare your graph from the data you recorded to the three graphs below. Which graph liand, move to an area of the classroom away from other students. Put on your safety does yours matc.h most closely? What doe.s your graph 1llustrat about the relationship goggles, and using the tubing as a handle, slowly begin to whirl the ball in a circular between the period of revolution and gravitational force? Explain. motion above your head and out away from your body. Make sure no one is near you, Graph #1 Graph #2 Graph #3 and that the ball's trajectory will not hit anything. Increase the speed of the ball's revolutions until the plastic tube with the washers moves up to a point just below your handle and maintains this relative position. Keep the orbiting motion steady and _ 8 regular, This may take some practice. g % 2 & 3 D. When you've mastered this motion, have one of your lab team members use a stopwatch 5'5 Ea ; or timer to time 10 complete revolutions of the ball, while the tube and washers maintain 3 2 = their position as described in Step C. Note your results, and determine the time for one gE' & E complete revolution of the ball by dividing the time by 10. Record your answer to the nearest tenth of a second in the Data Table provided. ; o . - 5 = Increasing Gravitational Force Increasing Gravitational Force Increasing Gravitational Force > > > NOTE: Make sure all team members are wearing safety goggles during this procedure in case the ball accidently comes loose. E. Repeat Steps C & D using 10, 15, 20, and 25 washers respectively. Record the period of revolution for each test in the Data Table, and graph your results. QUESTIONS (Part IT) 5. What do the washers represent in this model? 8. If you were to relate what you have learned in this exercise to the periods of revolution of - the nine planets in our solar system, how might you describe the effect a planet's distance from the sun has on its period of revolution? . 6. As more washers are added, what happens to the period of revolution? - 9. Ifthe speed of a satellite orbiting the earth began to decrease, how would its orbit change and why? i Gravity and Orbits Lab 6 Name: Date: DATA TABLE Number of Washers Period of Revolution 5 8.13 s 10 5.13 s 15 4.87 s 20 4 s 25 3.4 s GRAPH Period of Revolution (seconds) 5 10 15 20 25 # of Washers (Gravitational Force)