Skills Practice Lab DATASHEET A Energy of a Rolling Ball Raised objects have gravitational potential energy (PE). Moving objects have kinetic energy (KE). In this lab, you will find out how these two kinds of energy are related in a system in which a ball rolls down a ramp. WHAT YOU LL DO Measure the height, distance traveled, and time interval for a ball rolling down a ramp. Calculate the ball s potential energy at the top of the ramp and its kinetic energy at the bottom of the ramp. Analyze the results to find the relationship between potential energy and kinetic energy. WHAT YOU LL NEED balance board, at least 90 cm (3 ft) long box golf ball, racquet ball, or handball masking tape meterstick stack of books, at least 45 cm high stopwatch Holt Science Spectrum 57 Work and Energy
PROCEDURE Preparing for Your Experiment 1. Use the table below to record your data. DATA TABLE: POTENTIAL ENERGY AND KINETIC ENERGY Mass of ball (kg) Length of ramp (m) Height of ramp (m) Time ball traveled, first trial (s) Time ball traveled, second trial (s) Time ball traveled, third trial (s) Average time ball traveled (s) Average speed of ball (m/s) Final speed of ball (m/s) Final kinetic energy of ball (J) Initial potential energy of ball (J) Initial PE Final KE (J) Height 1 Height 2 Height 3 2. Measure the mass of the ball. (Hint: Make sure to set the balance to zero before you start.) Record the mass in your table in all three Ramp Height columns. 3. Place a strip of masking tape across the board close to one end. Measure the distance from the tape to the opposite end of the board. The distance must be measured in meters (m), or centimeters (cm). Record this distance in the row labeled Length of ramp. 4. Make a catch box by cutting out one side of a box. Holt Science Spectrum 58 Work and Energy
5. Make a stack of books approximately 15 cm high. Build a ramp like the one shown in the drawing by setting the taped end of the board on top of the books. Place the other end of the board in the catch box. Measure the vertical height of the ramp at the tape. Record this height in your data table in the row labeled Ramp Height 1. Making Time Measurements 6. First trial, Ramp Height 1: Place the ball on the ramp at the tape. Let the ball go, so that it rolls down the ramp. Use a stopwatch to measure the seconds the ball takes to travel to the bottom of the ramp. Record the time in your table. 7. Second trial and third trial, Ramp Height 1: Repeat step 6 two more times, and record the results in your table. After the third trial, calculate the average travel time and record it in your table. (Hint: To calculate the average time add the times for the three trials together and then divide the total by 3.) 8. Repeat steps 5-7 for two more ramp heights: Trials for Ramp Height 2: Using a stack of books that is approximately 30 cm high, repeat steps 5 7. Trials for Ramp Height 3: Using a stack of books that is approximately 45 cm high, repeat steps 5-7. Holt Science Spectrum 59 Work and Energy
ANALYSIS 1. Analyzing Data Calculate the average speed of the ball for each change in ramp height. Use the equation below to find the average speed. Record your answers in your data table. average speed length of ramp average time ball traveled Average speed for Ramp Height 1: Average speed for Ramp Height 2: Average speed for Ramp Height 3: Multiply the average speed by 2 to obtain the final speed of the ball and record the final speed. 2. Analyzing Data Calculate the final kinetic energy (KE) of the ball for each change in ramp height. Use the equation below to find the final kinetic energy (KE). Record the answers in your data table. KE 1 mass of ball ( final speed)2 2 KE 1 2 mv2 Final kinetic energy for Ramp Height 1: Final kinetic energy for Ramp Height 2: Final kinetic energy for Ramp Height 3: Holt Science Spectrum 60 Work and Energy
3. Analyzing Data Calculate and record the initial potential energy (PE) of the ball for each change in ramp height. Use the equation below to find the initial potential energy of the ball. Record your answers in your data table. grav.pe mass of ball 9.8 m/s 2 heightof ramp PE mgh Initial potential energy for Ramp Height 1: Initial potential energy for Ramp Height 2: Initial potential energy for Ramp Height 3: COMMUNICATING YOUR RESULTS 4. Making Comparisons Look at the potential energy at the top of the ramp for each of the three ramp heights. For each ramp height, is the ball s initial potential energy at the top of the ramp greater than, less than, or the same as the ball s kinetic energy at the bottom of the ramp? Ramp Height 1: Ramp Height 2: Ramp Height 3: Holt Science Spectrum 61 Work and Energy
5. Drawing Conclusions As the ramp height was raised, did the ball s potential and kinetic energy increase, decrease, or stay the same? EXTENSION Suppose that you perform this experiment and find that the values for kinetic energy are always just a little less than the values for potential energy. Did you do the experiment wrong? All of the potential energy should be converted to kinetic energy. What happened to the rest of the potential energy? Holt Science Spectrum 62 Work and Energy