Conservation of Energy Objective The objective of this lab is to experimentally verify the laws of conservation of energy. To do this you will release a steel marble from a series of heights and use an electronic timer to determine the speed of the steel marble at the bottom the aluminum track. You will then compare the predicted velocity of the ball with the experimental velocity, graph the results and calculate the experimental error. Materials Digital electronic timer Aluminum track Ring stand and pendulum support Clay Small steel ball (11mm) Digital Scale Ruler with millimeter measurements Meter stick Procedure 1. Write down the preliminary information in your lab notebook. Include a drawing of your set up in your lab notebook. Be sure to include a theory section in your introduction where you explain what formulas you are using and how and why they are being used in this experiment. 2. Use the ring stand to elevate the track and use a small piece of clay to keep it upright. Place two or three pieces of paper under the bottom of the track to stop the ball from bouncing as it hits the table. 3. Place the sensor gate at the bottom of the track so the ball will pass through without touching it. Turn on the electronic timer and set the function to “Timing I.” Timing I gives you a reading on the time it takes an object to completely pass in front of the sensor. 4. Use the digital scale to weigh the steel marble. Record the mass in your notebook. Don’t forget to convert the units to kg. 5. You will be releasing the ball from heights of 5cm (.05m) to 40cm (.40m) in 5cm increments. Use the meter stick to locate where the needed height is on the ramp. Calculate the potential energy of the ball at each height. This is the calculated or expected kinetic energy of the steel ball at the bottom of the ramp. 6. Place the ball at the appropriate height on the ramp. Use a pencil or ruler to release the ball without pushing it up the ramp; do not use your finger. You want the ball to accelerate from a complete stop. Allow the ball to roll down the ramp and through the gates and record the time from the timer. Place an object in the way or catch the ball so it does not hit the floor. 7. Repeat the experiment at least three times for each height. Record all of your trials and calculated speeds. 8. Average the times for each height and then calculate the ball’s average velocity. You will use this velocity to calculate the ball’s actual kinetic energy. Revised 3/10 9. Change the height of the ramp as needed and repeat the experiment for each of the required heights. Make sure you record all of your observations as well as results. Analysis 1. Use the velocity (speed) and mass of the steel marble to calculate the KE. Do this for each height and record your results in a table. Convert your PE and KE into mJ. Your results should be in a table with the columns shown below. Height Avg Time Avg Vel Calc KE (m) (ms) (m/s) PE (J) PE (mJ) (J) KE (mJ) 2. Create a graph with PE on the x-axis and the KE along the y-axis. Graph the theoretical KE (mJ) vs. PE (mJ) and make the points using an x. Then graph the actual KE (mJ) vs. the PE (mJ) and mark the points with a solid dot. Draw a trend line through each set of points. Remember to include the point (0,0) since a ball released from a height of zero has no potential or kinetic energy. 3. Calculate the percent error for each of the heights using the average KE and the formula: % Error = (|Actual results – Expected result|) x 100 Expected Results Questions 1. How can you explain the difference between the expected and the actual results? 2. If we removed the paper, the velocity of the ball drops. Explain why this happens? Feel free to experiment with this if you have time. 3. If instead of releasing the ball as instructed, you dropped the ball onto the ramp from a height of about 1cm above the ramp. Calculate and describe how this would change your results. 4. Does the angle of the ramp matter? In other words, will the KE results differ if you release it part way up a steep ramp rather than all the way up a shallow ramp if the height from the ground is the same? Explain. 5. If you were to do this lab again, what would you do to improve the accuracy of your results? 6. What specific recommendations do you have to improve this lab for next year’s students? Don’t forget a conclusion to your lab!
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