Kinetic and Potential Energy

Transcription

1 Kinetic and Potential Energy Intended for Grade: Fourth Subject: Science and Math Description: This activity demonstrates the difference between gravitational potential energy and kinetic energy and introduces the concept of energy conversion/conservation between potential and kinetic energy. Objective: The student will be able to explain the difference between the two states of energy and how it can be converted from potential to kinetic energy. Mississippi Frameworks addressed: Science Framework 9a: Differentiate energy as potential or kinetic energy. Science Framework 10a: Measure a given object using specified scientific measurement (English and/or metric). Science Framework 10b: Select, use, compare and convert within the appropriate standard (English and metric) system of measurement. Science Framework 10c: Identify the attributes of length, weight, capacity/volume, mass, time and temperature using English and metric units of measurement. Science Framework 10d: Calculate and solve problems with elapsed time. Math Framework 3b: Select, use, compare and convert within the appropriate standard (English and metric) system of measurement. Math Framework 3d: Identify the attributes of length, weight, capacity/volume, mass, time and temperature using English and metric units of measurement. Math Framework 3e: Calculate and solve problems with elapsed time. Math Framework 4a: Collect, organize, and interpret data, using bar graphs, circle graphs, line graphs, pictographs, charts, tables, and tally charts. NSF North Mississippi GK-8 1

2 Math Framework 4b: Formulate and solve problems that involve data analysis and prediction. Math Framework 5b: Determine whether estimated answers are reasonable and units are appropriate. National Standards addressed: Content Standard A: Science as Inquiry Content Standard B: Physical Science Math Standard: Measurement Math Standard: Problem Solving Math Standard: Data Analysis and Probability Math Standard: Number and Operations Math Standard: Reasoning and Proof Materials: Class: Metric Balance (one for the class) Jack-in-the-box or wind up toy Per Group: Car track (such as a Hot Wheels) Two cars (one should be heavier than the other) Ruler with centimeters Meter stick or measuring tape with centimeters Stopwatch Calculator Tape Three fishing weights or nickels 5 books (to prop the track on) Student s Experimental Procedure Kinetic and Potential Energy Data Sheet Background: Have you ever wondered why bubbles are round? Well, it is because of ENERGY! Everything has energy even things we don t naturally think of as having energy, such as thin soap films of bubbles and surfaces of objects. Shape is important when discussing energy of a surface, for example square objects have high surface energy at the corners whereas round objects have NSF North Mississippi GK-8 2

3 the lowest possible energy. Nature prefers objects to be at the lowest energy possible, so that thin film that creates a bubble takes on a round shape. There are other unexpected phenomena that depend on energy, such as sound. Sound is a type of mechanical energy that is created by compressing air. Light is also composed of energy and the different colors of light contain different amounts of energy. All types of matter have energy. Energy can be in different states and forms. The two states of energy are kinetic and potential energy. It is known that life depends on energy for existence, but what is energy? There are many definitions, but the simplest definition of energy is: Energy the ability to do work. Work is equal to a force, which is a push or pull on matter, times the distance that force causes the matter to travel. If no force is applied, then no work is done, but even if a force is exerted on matter and no distance is covered then still no work is done. So if a student pushes on his or her desk and the desk moves then work was done; however, if they push on the wall, the wall does not move and therefore no work was done. Energy has a set of unique properties: A. Energy can be transferred from one object to another. A good example of this principle is a moving object strikes a stationary object and the stationary object moves. To see this principle in action, get two marbles and roll one into the other and the one that was stationary will move. B. Energy can be converted (changed) from any state/form to another state/form. An example of changing state is a stationary object being put into motion. This changes potential energy into kinetic energy. C. Energy is always conserved; it can be neither created nor destroyed. The last property is very important. It is known as the law of conservation of energy. The most common conservation of energy is when potential energy is converted to kinetic energy or vise versa. Have you ever wound up a wind up toy or played with a jack-in-the-box? As you turn the crank, energy is being stored and that stored energy allows the toy to move when it is released. This is a good example of potential energy being converted to kinetic energy. NSF North Mississippi GK-8 3

4 As stated above there are two states of energy, kinetic and potential. These are the states of energy, just as solid, liquid, and gas are the states of matter. The basic definitions of the states of energy are: Kinetic Energy energy of motion. Potential Energy energy of position; stored energy. Kinetic energy is easy to recognize: if something is moving then it has kinetic energy. When an object has kinetic energy it can do work on other objects and do work as it moves. Potential energy is the exact opposite of kinetic energy. It is not causing anything to move nor is it doing work. Instead this state of energy is storing the energy that was given to it when work was done on the object. When matter has potential energy due to its height above the earth s surface, this is known as gravitational potential energy. The higher the object or the more it weighs the more gravitational potential energy the object will contain. Have you ever ridden a roller coaster and wondered why the first hill is so high? The gravitational potential energy at the top of the hill is great and when it is converted to kinetic energy, it is enough energy for the coaster to go down the hill, around a couple of turns and up another hill, so the reaction can start all over. What if the first hill was small? Would you be able to get up the next hill? Probably not. Procedure: 1. Introduce the concepts of kinetic and potential energy. 2. Use a jack-in-the-box or a wind up toy to demonstrate the conversion of potential to kinetic energy. 3. Designate an area for the balance and explain that the class needs to share it. 4. Divide the class into groups of four and assign each group an area. 5. Assign each member of the group a job. There will need to be 1 constructor, 1 timer, 1 measurer, and 1 recorder. 6. Distribute a copy of the Student s Experimental Procedure and to each student. 7. Distribute a copy of Kinetic and Potential Energy Data Sheet to the recorder of each group. NSF North Mississippi GK-8 4

5 8. Have the students perform the experiment described on the Student s Experimental Procedure and record their results. 9. As each group finishes, have them come up and record the data from the Summary Table of their data sheet on the blackboard or a poster board. 10. Discuss the experiment results as a class using the following questions: a. What main topics of energy did you learn about by completing this experiment? [Answer: The states of energy, potential (specifically gravitational) and kinetic energy, conservation/conversion of energy. The car had gravitational potential energy at the top of the ramp which was converted into kinetic when the car was released.] b. What did you observe about the heaviest (most mass) car? [Answer: This car had the most gravitational potential because it had the most mass and the most kinetic energy because it traveled the greatest distance.] c. What happened when the ramp height was lowered? [Answer: The car does not travel as far; therefore, the potential and kinetic energy was decreased.] d. What would happen if the track were covered in carpet? [Answer: The cars would have the same potential energy and this energy would be converted to kinetic, but it would not travel down the ramp as far because it would take more energy to travel over the carpet, expending the gravitational potential energy quicker.] e. Do you think all of the potential energy was converted to kinetic energy? Should it be? [Answer: The energies should be the same because energy can not be created or destroyed, but not all potential energy was converted to kinetic energy.] f. If all of the potential energy was not converted to kinetic energy, what do you think happened to the energy? [There are several correct answers. Possible ones: Energy is lost due to contact between the wheels NSF North Mississippi GK-8 5

6 and the track, the car lost energy due to air resistance (it had to do work on the air to travel down the ramp).] 11. Have the students complete the journal questions. Evaluation: Students successfully perform the experiment, complete the worksheet, and participate in class discussion. The teacher will have to monitor these accomplishments. Extended Activities: Many different activities demonstrate potential and kinetic energy and the conversion of energy from one state to another. The following is a short list of activities on the internet: A. Racing Slinkys This activity demonstrates gravity, potential energy, and kinetic energy as a slinky walks down stairs or an incline. This activity can be found at B. Physics of Roller Coasters This website lets students build their own roller coaster and then try it to see if it works. This teaches the student that the first hill has to be higher than the second hill, so that the coaster has enough energy to get to the top of the second hill. Website: C. Another activity helps the students construct their own rollercoaster. This activity may take the students a while to complete. They make their own coaster out of wire. o68.htm. D. Roll Back Toy the students construct a toy that demonstrates potential and kinetic energy. There are other ideas on this page as well. s.htm E. Rubber Bands and Springs: Potential Energy Converted to Kinetic Energy This activity was developed by K NEX Education. The class will need a K NEX set with enough pieces NSF North Mississippi GK-8 6

7 for at least four groups. Some students may find constructing the car from the K NEX difficult. Go to and register and then you can access the lesson plans. F. Also check out Sources: Maton, Anthea, et al. Exploring Physical Science. New Jersey: Prentice Hall, Serway, Raymond A., Robert J. Beichner, and John W. Jewett, Jr. Physics For Scientists and Engineers, 5 th ed. Fort Worth: Saunders College Publishing, New Mexico Solar Energy Association: Energy Concepts Primer. Accessed June r.htm. Activity Idea: CARS and ENERGY by Judy Schneider. Accessed June Mo68.htm. Prepared by: Brittany Hancock NSF NMGK-8 University of Mississippi April 2006 NSF North Mississippi GK-8 7

8 Student s Experimental Procedure 1. As a group, decide the height of the track. It should be no higher than 5 books stacked on top of one another. 2. As a group, answer the first two questions on the Kinetic and Potential Energy Data Sheet. This will be the group s hypothesis (proposed solution to a scientific problem) for the experiment. 3. Constructor: Construct the track. It will look like Figure 1. Use books to raise one end of the track. Track Figure 1: Car Track 4. Measurer: Help the constructor. 5. Timer and Recorder: Weigh the cars with the balance. If the cars do not have at least a 20 gram difference in weight, attach three nickels to the top of the heaviest car with tape. Place the tape from the front bumper to the back bumper, so that it will not prevent the wheels from rolling properly. Reweigh that car. 6. Recorder: Record the mass in grams for each car on the data sheet. 7. Cut out the Car 1 and Car 2 labels below. CAR 1 CAR 2 8. Tape the Car 1 label on the heavier car. 9. Tape the Car 2 label on the other car. 10. Measurer: After the track is setup, measure the height of the track from the floor to the start of the track. NSF North Mississippi GK-8 8

9 11. Recorder: Record this height on the data sheet. 12. Measurer: Measure the length of the track. 13. Recorder: Record the length on data sheet. 14. Constructor: Place one car at the top of the ramp. Release the car. 15. Timer: Time the car from the moment of release until it comes to rest somewhere at the bottom of the track with the stopwatch. 16. Recorder: Record the time in seconds. 17. Measurer: Use the tape measure to measure the distance traveled by the car from bottom end of the track to the back bumper of the car. Have one of your group members hold the end of the tape measure. Call out the distance to the recorder. 18. Recorder: Add the length of the track to this distance and record the distance in centimeters. 19. Repeat steps 14 through 18 two more times for that car. 20. Now repeat steps 14 through 19 for the other car. 21. Recorder: With the help of the group, average the time and distance for each car. Record it on the data sheet. 22. Constructor: Lower the ramp by at least 3 centimeters (remove at least one book). 23. Measurer: Measure the lowered height of the ramp. 24. Recorder: Record the new height on the data sheet. 25. Using Car 1, repeat steps 14 through 18 three times. 26. Recorder: With the help of the group average the time and distance of the car. Record it on the data sheet. 27. Recorder: With the help of your group complete the Summary Table and Bar Graph. 28. Recorder: Post the answers from the Summary Table with the rest of the class as assigned by the teacher. 29. Everyone in the group complete the journal questions. NSF North Mississippi GK-8 9

10 Members of Group: Kinetic and Potential Energy Data Sheet 1. Which car does your group think will travel the farthest and why? 2. What effect if any will lowering the track have on the car s potential energy? Table 1: Description and weight of each car Car 1 Car 2 Description Mass grams grams Height of Track: centimeters Length of Track: centimeters NSF North Mississippi GK-8 10

11 Members of Group: Table 2: Distance traveled by each car on high track Car 1 Car 2 Time Distance* Time Distance* seconds centimeters seconds centimeters Average *Don t forget to add the length of the track to the distance the car traveled and then record the distance. *Remember to average: add up the 3 numbers and then divide by 3. Height of Lowered Track: centimeters Table 3: Distance traveled by Car 1 on low track Results for Car 1 on Lower Track Time seconds Distance centimeters Average NSF North Mississippi GK-8 11

12 Members of Group: Table 4: Summary Table* Summary Table Height of high track: Height of low track: Unit Car 1 on high track Car 2 on high track Car 1 on low track Mass grams Average Time seconds Average Distance centimeters *All of this information can be found in Tables 1-3. Graph 1: Bar graph of average distance traveled by each car 800 Distance Traveled by each Car 700 Distance (centimeters) Car 1 on High Track Car 2 on High Track Car 1 on Low Track NSF North Mississippi GK-8 12

13 Name: Kinetic and Potential Energy Journal 1. What type of energy does the car have when it is perched atop the ramp? 2. What happens to that energy when the car moves down the ramp? 3. Which car do you think had the most kinetic energy? 4. Which car do you think had the most potential energy? 5. Are they the same? Why or why not? 6. What did you learn from this experiment? NSF North Mississippi GK-8 13