Experimenting with Gravity

Experimenting With Gravity

Suggested TEKS: Grade Level: 6 Math - 6.11 Science - 6.12 Suggested SCANS: Time Required: 1 to 2 class periods Interpersonal. Participates as a team member. National Science and Math Standards Science as Inquiry, Earth & Space Science, Physical Science, Computation, Measurement, Observing, Communicating Countdown: Low wooden chair or stool 3 types of balls (ping pong, tennis, golf) Paper Ruler Textbook Pencil Table Small water balloons String Tape Shoe Box Small lingerie bag/stocking Newspaper/Styrofoam peanuts Various kinds of packing materials

Ignition: Gravity is the natural force that causes objects to move toward each other. The strongest pull of gravity in our world is from the middle of the earth. When you throw a ball into the air, gravity pulls it down. When you sit on the sofa, gravity holds you down. Also, when you walk and run, gravity keeps your feet near the ground. Without gravity, we would have no “staying force” and would float off into outer space. Moons, satellites, and spacecraft orbit planets, like earth, due to their strong gravitational fields. The planets, in turn, orbit the sun because of its massive gravitational pull.

Liftoff: A. Since you cannot see gravity, how can you prove that it’s around you?

Using one low durable chair or stool, 1) Place the chair in front of you. From the floor, jump up onto the seat of the chair. Next, jump back down. Notice the difference: which action required you to exert more energy? 2) Repeat the procedure, this time closing your eyes. How do you feel?

Conclusion: It is a lot harder to jump up onto the chair rather than to jump down. The reason is that when you jump up, you’re jumping against the force of gravity. When you jump down, you’re jumping toward the force of gravity. The gravity itself is doing all of the work; all you need to do is to step off the seat.

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B. Do heavier objects fall faster than lighter objects?

Using a ping pong ball, a golf ball, a tennis ball, and a wooden chair: 1) Stand on the chair, holding the ping pong ball in one hand and the golf ball in the other. Hold them out in front of you as high as you can and drop them simultaneously. Observe when both balls hit the floor. 2) Follow the same procedure, using the golf ball and the tennis ball. Finally, use the ping pong ball and the tennis ball.

Conclusion: Each pair of balls hits the floor at the same time. This is due to the fact that gravity acts upon all forces equally. Objects accelerate at the rate of 32.14 feet per second², every second. This is called the “acceleration of free fall”. (9.8 m/s²)

C. Does an object’s shape affect its speed?

Using a ball of crumpled paper, an unfolded sheet of paper, and a wooden chair: 1) Stand on the chair, holding the crumpled paper in one hand and the unfolded paper in the other. Hold both as high as possible; release them at the same time.

Conclusion: The crumpled paper hits the floor first. The air that hit the under-surface of the unfolded paper slowed its rate of fall.

D. How do you find an object’s center of gravity?

Using a ruler, pencil, textbook, and a table or counter top: 1) Place the ruler on the end of the table. Slowly begin to push it toward the table’s edge. Keep pushing, until it eventually falls to the floor. 2) Repeat the same procedure with the pencil and the textbook.

Conclusion: Each object eventually reaches the point where all of its weight is concentrated at its “center of gravity”. When it passes this point, it is no longer balanced and falls to the floor.

E. Can the impact of a falling object be cushioned from impact by certain insulating materials?

Using small water balloons, string, tape shoe box, newspaper, Styrofoam peanuts, small lingerie washing bag, insulating materials: 1) One or two weeks prior to the beginning of this experiment, ask students to collect different types of packaging materials and bring them to school. 2) Emphasize to students that the objective of this activity is to design a package that will cushion the water balloon – a fragile object – and thereby absorb some of the force of the landing. If they are successful, the balloon will not break. 3) Have students work in pairs or small groups and experiment with different types and shapes of boxes, as well as insulating materials. A few suggestions might be to plan to completely

SpaceExplorers http://www.tsgc.utexas.edu/spaceexplorers/ 119 Orbital Mechanics: Experimenting With Gravity Texas Space Grant Consortium http://www.tsgc.utexas.edu/ surround the water balloon with “absorbing materials”. Another is to suspend the water balloon in the middle of the box, inside a lingerie bag or stocking, and to tie the bag securely to both ends of the box with string. 4) Assign a group leader to write up the experiment, using the following format: Problem: Which material is the best insulator? Hypothesis: We think . . . Procedure: Data Analysis: Table showing materials used Conclusion: 5) On the day of the experiment, make sure that the balloons are fully filled. Use the football bleachers (or outside steps) as your site. Determine 3 - 5 different heights from which to drop the balloon packages. Insure that each group drops its package as uniformly as possible. 6) Record in a table/chart the type of package used by each group and the results from different heights. 7) Conclusion: Elicit a discussion comparing the water balloon results with the landing of the space shuttle on earth. Also, ask for predictions as to how future spacecraft will land on Mars, which has an estimated surface gravity of .38 that of the earth.

More ideas … ¾ Find the center of gravity for several objects. To start, make a cardboard model of a simple boat. Then, using an unsharpened pencil, form a pivot from which the boat can hang. Hang a length of weighted thread from the same pivot. Trace the line of the thread on the cardboard. Repeat the same procedure with 2 other pivot points. The center of gravity is the intersection of the 3 lines. This same process can be done with a cardboard model of an airplane, space shuttle, and other spacecraft. ¾ Design an experiment. Plants respond to the earth’s gravity. Plant stems grow in the opposite direction to the pull of gravity. Plant roots, however, grow downward in the direction of gravity. Use each of the experiment components listed below: Purpose List of materials Step-by-step procedure (which uses both a control and a variable) Observations Record Conclusion based on data

SpaceExplorers http://www.tsgc.utexas.edu/spaceexplorers/ 120 Orbital Mechanics: Experimenting With Gravity Texas Space Grant Consortium http://www.tsgc.utexas.edu/