Name Class Date. marker and the meterstick to mark points on the string that are 50 cm, 70 cm, and 90 cm away from the mass.

Transcription

1 Name Class Date A pendulum clock is a compound machine that uses stored energy to do work. A spring stores energy, and with each swing of the pendulum, some of that stored energy is used to move the hands of the clock. In this lab, you will take a close look at the energy conversions that occur as a pendulum swings. marker mass, hooked, 100 g meterstick string, 1 m SAFETY INFORMATION PROCEDURE 1. Make a pendulum by tying the string around the hook of the mass. Use the marker and the meterstick to mark points on the string that are 50 cm, 70 cm, and 90 cm away from the mass. 2. Hold the string at the 50 cm mark. Gently pull the mass to the side, and release it without pushing it. Observe at least 10 swings of the pendulum. 3. Record your observations. Be sure to note how fast and how high the pendulum swings. 4. Repeat steps 2 and 3 while holding the string at the 70 cm mark and again while holding the string at the 90 cm mark. ANALYZE THE RESULTS 1. List similarities and differences in the motion of the pendulum during all three trials. Holt Science and Technology 80 Energy and Energy Resources

2 Name Class Date continued 2. At which point (or points) of the swing was the pendulum moving the slowest? the fastest? DRAW CONCLUSIONS 3. In each trial, at which point (or points) of the swing did the pendulum have the greatest potential energy? the least potential energy? (Hint: Think about your answers to question 2.) 4. At which point (or points) of the swing did the pendulum have the greatest kinetic energy? the least kinetic energy? Explain your answers. 5. Describe the relationship between the pendulum s potential energy and its kinetic energy on its way down. Explain. 6. What improvements might reduce the amount of energy used to overcome friction so that the pendulum would swing for a longer period of time? Holt Science and Technology 81 Energy and Energy Resources

3 Teacher Notes and Answer Key TIME REQUIRED One 45-minute class period LAB RATINGS Teacher Prep 1 Student Set-Up 1 Concept Level 2 Clean Up 1 Easy Hard Edith C. McAlanis Socorro Middle School El Paso, Texas The materials listed are for each student. SAFETY CAUTION Caution students to swing the pendulum gently. Students should be a reasonable distance from one another and from classroom equipment. Students should wear safety goggles. Holt Science and Technology 95 Energy and Energy Resources

4 Name Class Date A pendulum clock is a compound machine that uses stored energy to do work. A spring stores energy, and with each swing of the pendulum, some of that stored energy is used to move the hands of the clock. In this lab, you will take a close look at the energy conversions that occur as a pendulum swings. marker mass, hooked, 100 g meterstick string, 1 m SAFETY INFORMATION PROCEDURE 1. Make a pendulum by tying the string around the hook of the mass. Use the marker and the meterstick to mark points on the string that are 50 cm, 70 cm, and 90 cm away from the mass. 2. Hold the string at the 50 cm mark. Gently pull the mass to the side, and release it without pushing it. Observe at least 10 swings of the pendulum. 3. Record your observations. Be sure to note how fast and how high the pendulum swings. 4. Repeat steps 2 and 3 while holding the string at the 70 cm mark and again while holding the string at the 90 cm mark. ANALYZE THE RESULTS 1. List similarities and differences in the motion of the pendulum during all three trials. Accept all reasonable answers. Holt Science and Technology Energy and Energy Resources

5 Name Class Date continued 2. At which point (or points) of the swing was the pendulum moving the slowest? the fastest? slowest when it is first released and when it is at the top of the opposite side; fastest at the bottom of its swing during each trial DRAW CONCLUSIONS 3. In each trial, at which point (or points) of the swing did the pendulum have the greatest potential energy? the least potential energy? (Hint: Think about your answers to question 2.) greatest potential energy at the greatest height on either side; smallest potential energy at the bottom of its swing 4. At which point (or points) of the swing did the pendulum have the greatest kinetic energy? the least kinetic energy? Explain your answers. greatest kinetic energy at the bottom of its swing (moving fastest); smallest kinetic energy at the top of its swing (moving slowest) 5. Describe the relationship between the pendulum s potential energy and its kinetic energy on its way down. Explain. The pendulum s kinetic energy increases on its way down (as the pendulum speeds up). As the pendulum moves from its highest point to its lowest point, potential energy decreases. 6. What improvements might reduce the amount of energy used to overcome friction so that the pendulum would swing for a longer period of time? Accept all reasonable answers. Holt Science and Technology Energy and Energy Resources