Bowen, Sheila J. Gwendolyn Brooks Junior High

Objective(s): Students will be able to explain inertia. Students will be able to identify the factors that determine inertia. Students will be able to compare the acceleration of an object with a net force to an object without a net force. Students will be able to state Newton's first law of motion. Apparatus Needed: Card table, tablecloth, two china plates, heavy plastic plate, light plastic plate, styrofoam or paper plate, plastic drinking glass, index card, two pennies, five nickels, paper disc, small plastic disc, three-wheeled cart or rollerskate, dot/tape time, two identical shaped objects of different weights, 500 gram weight, distance/time posterboard graph, average/speed posterboard graph, paste or tape. Recommended Strategy: Students should have prior knowledge of speed and acceleration measurements and graphing. Demonstrate inertia by snatching a tablecloth from under two china plates. Student teams are to complete and write up the following activities. Each write up should include a prediction and an explanation of what happened and why. Activity 1 - Place a heavy plastic plate in the center of the table on a tablecloth. Then snatch the tablecloth from under the plate. Repeat this activity using a light plastic plate and then a styrofoam plate. Activity 2 - Place an index card flat on top of a plastic drinking glass. Place a penny on the center of the card. Hold the base of the glass with one hand. Then using the forefinger of the other hand, flick the card forward so it moves out from under the penny. Repeat this activity using a plastic disc and then a paper disc. Activity 3 - Stack 4 nickels one on top of the other. Using your forefinger, flick another nickel sharply against the bottom coin of the stack. Repeat this activity using the penny and then the plastic disc. After the activities, conduct a classroom discussion of factors of inertia observed in each activity. Next have each student handle two objects, identical in shape and appearance but different in weight, to distinguish which has the greatest inertia. Set up demonstration using a three-wheel cart or rollerskate with an accelerometer on top. Attach the end of two tapes from the dot/tape timer to the cart. Start the timer and give the cart an initial push. Impress on students to observe the accelerometer. Have two students, one for each tape, mark and cut the tape into a series of four dot strips. Take the first strip of one of the students and paste or tape it in the lower left corner vertically on the distance/time posterboard graph. Then take the second strip and paste it with its lower left corner next to the upper right corner of the first strip. Continue pasting each successive strip until you get to the top of the graph. Draw a line connecting the top of the strips. With the second set of tape strips, lay them one at a time next to each other on the horizontal axis of the average speed/time posterboard graph. Start with the first strip to the end of the graph. Draw a line across the top of the strips. Next tie a cord to the cart and place the other end through a pulley at table level and then up to a pulley on a ringstand. Attach the 500 gram weight to the end of the cord. Once again attach two tapes from the dot/tape timer to the cart. Repeat the demonstration releasing the weight. Then tape the strips in the same way to each of the posterboard graphs. The class should then compare and explain both graphs. Then discuss inertia, its factors and Newton's first law.
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