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Rolling Returns Category: Physics Type: Make & Take Rough Parts List: 1 2 1 5 2 Large coffee canister Large rubber bands Pipe cleaner Weights (nuts or beads) 3” pieces of dowel Tools List: Drill with bit, or punch Video: http://youtu.be/6L8OClcEGPg How To:
Drill or punch a hole in the lid of a coffee can. Turn the can and drill an identical hole through the bottom. Thread the nuts onto the pipe cleaner. Twist the pipe to secure the nuts in place. © 2012 Fresno Community Science Workshop. All Rights Reserved worldwide. When linking to or using FCSW content, images, or videos, credit MUST be included. Tie the first rubber band to the pipe cleaner. Fold down any excess pipe cleaner. Tie the second rubber band to the first so that it will stretch out to the sides. Pull the second rubber band out to the sides to ensure the knot is secure enough. Poke one end of the free rubber band through the bottom of the can and thread a dowel through the loop. Pull the other end of the elastic through the can. Poke it through the hole in the lid and thread the second dowel through it. It’s now ready to roll! Give it a good-­‐sized shove forward on a smooth surface and see if it comes back to you. © 2012 Fresno Community Science Workshop. All Rights Reserved worldwide. When linking to or using FCSW content, images, or videos, credit MUST be included. Fine Points: An empty tennis ball container or another cylinder can be used instead of the coffee canister. Don’t use a glass jar; it could break. Small containers can be hard to thread the rubber bands through. If it’s hard to pull the elastic through the holes, use a small flat-­‐blade screwdriver or a pair of tweezers to help. → You can also roll it firmly in one direction, say 3 revolutions then let it go and watch it go back and forth with a pendulum-­‐like motion. →
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Kinetic energy is energy of motion. Potential energy is stored energy. Energy transfer is the moving of energy from one object or material to another. Focus Questions: 1. Why do you think the can rolls back? 2. What do you think would happen if the nuts were removed? 3. Do you think the can would roll faster or slower with more weight? With less weight? Elaboration: The Rolling Returns can is an example of transfer of energy between kinetic and potential energy. Kinetic energy is the energy an object has due to its motion. Potential energy is stored energy. According to the principle of conservation of energy, energy is never created or lost, but rather transferred from one form to another. In any situation, you can look for the path of the energy, start to finish. In this project, before you begin the can is not moving and has no potential energy to do anything. You have potential energy in your body due to the food you ate earlier. When you push the can forward, you give some of your energy to the can. As the can rolls away from you it has kinetic energy. The kinetic energy of something depends on its speed and its mass. Inside the can the nuts are hanging down without spinning as the can rolls but the rubber bands are getting twisted with every turn. This stores potential energy in the rubber bands. As the rubber bands twist, they push back on the can slowing it down. Eventually it stops. At this point its kinetic energy is zero and its potential energy is at a maximum. As the can rolls back to you, the rubber bands unwind and the potential energy stored in them converts back into kinetic energy. Since the rubber bands were twisted in one direction as the can rolled away from you, they untwist in the opposite direction, causing the can to move in the opposite direction back towards you. The nuts on the pipe cleaner attached to the rubber band inside the can act as a weight, and this is key for the transfer of energy we see. The weight is subjected to a twisting force from the rubber band, but it is also being pulled down by gravity. The force being exerted by gravity on the nuts is greater than the twisting force of the rubber band on them. As long as the weight never goes up over the rubber band, the rubber band will continue to twist. If the nuts do go up over the rubber band you’ll feel or hear them, and the car will lose some energy. Links to k-­‐12 CA Content Standards: Grades k-­‐8 Standard Set Investigation and Experimentation: Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other strands, students should develop their own questions and perform investigations. © 2012 Fresno Community Science Workshop. All Rights Reserved worldwide. When linking to or using FCSW content, images, or videos, credit MUST be included. Grades k-­‐12 Mathematical Reasoning: 1.0 Students make decisions about how to approach problems: 1.1 Analyze problems by identifying relationships, distinguishing relevant from irrelevant information, sequencing and prioritizing information, and observing patterns. 1.2 Determine when and how to break a problem into simpler parts. 2.0 Students use strategies, skills, and concepts in finding solutions: 1.1 Use estimation to verify the reasonableness of calculated results. 1.2 2.2 Apply strategies and results from simpler problems to more complex problems. 1.3 Use a variety of methods, such as words, numbers, symbols, charts, graphs, tables, diagrams, and models, to explain mathematical reasoning. 2.5 Indicate the relative advantages of exact and approximate solutions to problems and give answers to a specified degree of accuracy. 3.0 Students move beyond a particular problem by generalizing to other situations: 3.1 Evaluate the reasonableness of the solution in the context of the original situation. 3.2 Note the method of deriving the solution and demonstrate a conceptual understanding of the derivation by solving similar problems. 3.3 Develop generalizations of the results obtained and apply them in other circumstances. Grade 2 Standard Set 1. Physical Sciences. The motion of objects can be observed and measured. As a basis for understanding this concept: 2.c. Students know the way to change how something is moving is by giving it a push or a pull. The size of the change is related to the strength, or the amount of force, of the push or pull. Grade 3 Standard Set 1. Physical Sciences. Energy and matter have multiple forms and can be changed from one form to another. As a basis for understanding this concept: 1.b. Students know sources of stored energy take many forms, such as food, fuel, and batteries. 1.c. Students know machines and living things convert stored energy to motion and heat. 1.d. Students know energy can be carried from one place to another by waves, such as water waves and sound waves, by electric current, and by moving objects. Grade 8 Standard Set 2. Forces. Unbalanced forces cause changes in velocity. As a basis for understanding this concept: 2.a. Students know a force has both direction and magnitude. 2.b. Students know when an object is subject to two or more forces at once, the result is the cumulative effect of all the forces. 2.c. Students know when the forces on an object are balanced, the motion of the object does not change. 2.d. Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or compression in matter, and friction. © 2012 Fresno Community Science Workshop. All Rights Reserved worldwide. When linking to or using FCSW content, images, or videos, credit MUST be included.