6 Energy.docx

Physics Lab (Online Simulation) ENERGY Mechanics TA name: Date: Student Name: Student ID: Simulation Activity #4: Energy Skate Park Simulation created by the Physics Education Technology Project (PhET) c/o The University of Colorado at Boulder http://phet.colorado.edu/ Link: http://phet.colorado.edu/simulations/sims.php?sim=Energy_Skate_Park

Physics Lab (Online Simulation) Investigating Energy Exchanges: Kinetic Energy and Gravitational Potential Energy Objective: This online activity is intended help you learn more about physics. We offer this lab in the hope that you will make connections between predictions and conclusions, concepts and actions, equations, and practical activities. Give this lab a chance! You will learn a lot, and you might even enjoy it! Answer all the questions as you follow the procedure and run the simulation. Learn about conservation of energy with a skater dude ! (Or gal. The simulation has been updated.) Build tracks, ramps and jumps for the skater and view the kinetic energy, potential energy and friction as he moves. You can also take the skater to different planets or even space! Take some time and familiarize yourself with the simulation. Track selector: You can pick one of several pre-made tracks to test the skater on. Reset: This button will reset everything. Skater selector: You can pick any skateboarder you like ( Hint: different skateboarders have different masses) Measuring Tape: Check the Measuring Tape Box when you want to make measurements. Drag the left end of the tape measure to where you start your measurement, and then drag the right end to the final location. To make a reference horizontal line to your measurement, check the potential energy reference box and drag the blue line you see on the screen to the initial position. Graph Selector: Under the “graphs” tab, you can toggle various graphs that give you information about the skater. You can also add a pie graph by checking the show pie chart box. These graphs can be shown with or without the loss due to thermal energy. Gravity: You may change the force of gravity by changing the location or the sliding bar underneath Gravity box. Introduction: The law of conservation of energy states that the total amount of energy in an isolated system remains constant. As a consequence of this law, we can say that energy neither created nor destroyed, but can change its form. The total energy of a system (the sum of its mechanical energy and its internal energies, including 𝐸 thermal energy) can change only by amounts of energy that are transferred to or from the system. If work is done on the system, then 𝑊 𝑊 = 𝐸 = 𝐸 ?𝑒𝑐ℎ + 𝐸 𝑡ℎ + 𝐸 𝑖?𝑡 If the system is isolated ( ), this gives 𝑊 = 0 𝐸 ?𝑒𝑐ℎ + 𝐸 𝑡ℎ + 𝐸 𝑖?𝑡 = 0 The skate park is an excellent example of the conservation of energy. For the isolated skate-track-Earth system, the law of conservation of energy equation has the form 𝐸 ?𝑒𝑐ℎ + 𝐸 𝑡ℎ = 0

Physics Lab (Online Simulation) e. Open the Energy versus Time graph f. Run the simulation for 20 seconds 9. What are the energies at 12 seconds and 17 seconds? a. at 12 seconds: K = _4.36_______ J U = _2311.4_______ J E th = _1636.66_______ J b. at 17 seconds: K = __1.79______ J U = _1876.75_______ J E th = _2073.9_______ J 10. Calculate the change and total energies a. Δ K = __2.57______ J Δ U = __-434.7______ J Δ E th = _437.24_______ J b. Total energy: Δ E = Δ K + Δ U + Δ E th = __0.01_______ J Part II: Double Well (Graphs -> Select Track) 1. Click Reset and return skater buttons and use the reference height shown above. Measure height of each control point from the reference line and calculate the potential (U), kinetic (K), and total (E) energies. a. At point 1: h 1 = 5.43___ m. U 1 = _3492_____J K 1 = 25______J E 1 = 3517______ J b. At point 2: h 2 = _0__ m. U 2 = _27.89_____J K 2 = _3489_____J E 2 = _3517_____ J c. At point 3: h 3 = _3.59__ m. U 3 = _2956_____J K 3 = _561_____J E 3 = __3517____ J d. At point 4: h 4 = _2.27__ m. U 4 = _1657_____J K 4 = _1859_____J E 4 = _3517_____ J 2. Calculate the speeds at control points 3 and 4 using the kinetic energies result you calculated in the previous step. a. The skater’s speed at point 3: v 3 = _3.33______m/s b. The skater’s speed at point 4: v 4 = __3.36_____m/s

Physics Lab (Online Simulation) 3. Now open the Energy vs position graph and read the potential (U), kinetic(K), and total (E) energies at the control points a. At point 1: U 1 = 3492______J K 1 = 25______J E 1 = _3517_____ J b. At point 2: U 2 = _27.89_____J K 2 = 3489______J E 2 = _3517_____ J c. At point 3: U 3 = _2956_____J K 3 = _561_____J E 3 = __3517____ J d. At point 4: U 4 = _1657_____J K 4 = 1859______J E 4 = _3517_____ J 4. Calculate the heights at each of the control points using the information from step 3. a. h 1 = 5.43____ m, h 2 = 0____ m, h 3 = 3.59____ m, h 4 = _2.27___ m, h 5 = _8.25___ m. 5. How are the shapes of the potential and kinetic energy graphs related to the shape of the track? a. Potential energy to the track: _begins around the same kinetic, but decreases as the skater went down the ramp. b. Kinetic energy to the track: __ _decreases as the skater goes up the ramp. 6. If you change the location to Moon instead of Earth, will the shape the energies change? If not, what is changed? shape energies won't change, but the total energy will be due to changes in the gravitational constant. 7. Apply the following settings for the simulation to answer the proceeded questions. a. Stop the simulation b. Make sure the simulation is paused , and drag the skater to the top. c. Adjust the friction slider to one-fourth of the distance between “None” and “Lots”. d. Open the Energy versus Time graph e. Run the simulation for 20 seconds 8. What are the energies at 9 seconds and 16 seconds a. at the 9 th second: K = _916_______ J U = __1778______ J E th = __1257______ J b. at the 16 th second: K = __ _356_____ J U = _1397_______ J E th = __2198______ J 9. Calculate the change and total energies. E th is thermal energy a. Δ K = __-560______ J Δ U = __-381______ J Δ E th = __941______ J b. Total energy: Δ E = Δ K + Δ U + Δ E th = __ _0_ _____ J Follow up Questions: 1. At the highest point kinetic energy is (zero / maximum) while the potential energy is (zero /maximum). 2. At the lowest point kinetic energy is (zero / maximum ) while potential energy is (zero /maximum). 3. Mass ( affects / does not affect) the conservation of energy. 4. How much potential energy does a 60. kg skater have before she starts her ride, 12 m above the ground? _ 7056_ __ 5. How much kinetic energy does a 60.0 kg skater have traveling with a velocity of 4 m/s? ____ _480 J_ _____________ 6. How fast must a 20. kg skater travel to have a kinetic energy of 360 Joules? _______ 6 m/s__ ___________________