Mr. Pomerantz Page 1 of 5 A swinging pendulum keeps a very regular beat. It is so regular, in fact, that for many years the pendulum was the heart of clocks used in astronomical measurements at the Greenwich Observatory. There are at least three things you could change about a pendulum that might affect the period (the time for one complete back and forth swing) the release point (angle) of the pendulum the length of the pendulum, measured from the center of the pendulum bob to the point of support the mass of the pendulum bob To investigate the pendulum, you need to do a controlled experiment; that is, you need to make measurements, changing only one variable at a time. Conducting controlled experiments is a basic principle of scientific investigation. In this experiment, you will count how many periods (one complete swing of a pendulum, back and forth) there are in one minute. The purpose of this lab is to determine what variable affects the period of a pendulum. By conducting a series of controlled experiments with the pendulum, you can determine how each of these quantities affects the period. Problem: To determine how to increase the period of a pendulum Experiment #1 How does changing the mass of a pendulum affect the number of periods in one minute? Independent Variable Dependent Variable Constant Variables 1. Take a paper clip and bend it into a hook shape at the bottom and a loop at the top. See figure to the left for an example. 2. Next, thread a piece of string through the loop of the paper clip and tie securely. 3. Now carefully tape the pendulum to the table, making sure it can swing back and forth. 4. Add one washer as the mass to the paper clip and record how many times the pendulum swings back and forth in one minute. Remember one back and forth swing equals one period. Record this data in data table. Please release the pendulum from the same angle each time. 5. Repeat step, 4. four more times with different masses and record data Data table experiment #1 Pendulum mass as number of washers 1 Periods (# of back & forth swings in 1 minute) Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 2 3 4 5
Mr. Pomerantz Page 2 of 5 Experiment #2 How does changing the length of the pendulum affect the number of periods in one minute? Independent Variable Dependent Variable Constant Variables 1. First, change the length of the pendulum so it is 30 cm in length. Measure from the top of the paper clip to where the pendulum is attached to the table. 2. Next, add 2 washers to the pendulum for the duration of this experiment. 3. Decide on release angle and keep constant throughout the experiment. Remember variables should always be kept constant. 4. Now, release the pendulum and count the periods in one minute. Do this five times for each length and record data in data table. Data table Experiment #2 Pendulum length (cm) 30 Periods (# of back & forth swings in 1 minute) Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 25 20 15 10 Graph the date for each experiment. Be sure to follow proper graphing procedure.
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Mr. Pomerantz Page 5 of 5 Create an executive summary of the University of Arizona pendulum investigation. The summary should follow the format below: Executive summary format: Begins with a two sentence introduction explaining the objective of the intestigation. Seven to ten bullet points (sentence fragments) follow the intro. The bullets points should contain the most essential information in the intevestigation (relating to procedure, variables and purpose). Complete the summary with a two sentence conclusion explaining why the lab is relevant to its target audience (the target audience is a 9 th grade science class).