Exploring the Law of Conservation of Energy

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Objective

SWBAT describe how energy cannot be created or destroyed but instead is transferred.

Big Idea

Using toys and other fun props, your students can explore how energy transfers help scientists and engineers to innovate.

Engage

45 minutes

I like to start by getting my students to argue with me. My strategy is to give students the opportunity to confront their misconceptions and to consider the plausibility of a different answer. I begin by saying: 

"Energy cannot be created or destroyed, it can only be transferred. If that is true, all of the energy in the universe will never change. Who can prove me wrong and give me an energy that CAN be created or destroyed?"

My student responses range from confusing to hilarious as the kids try to prove me wrong. As the students give me their answers I promote their thinking with specific teacher talk using phrases such as, "I like the way you are thinking. Have you thought about this?" For example every year a child will say that lightning is created energy. I answer, "Interesting idea. It seems right, doesn't it? Can anyone tell me why we have lightning?" The conversation ebbs and flows. At a point on the edge of class frustration, I ask kids to divide. "If you believe lightning creates energy stand by the door. If you think lightning doesn't create energy stand by the white board." The collaboration of understanding and misconception come together.  Students will change sides during the discussion as more information is added.

When all of the students have moved to the Not-Create-Energy side of the room, I ask, "What changed your mind?" I promoting learning through reflection by allowing students to dig deeper into their understandings. I allow a variety of students to express their understandings in ways to teach others. Many times I get the answer, "I was thinking like Dakota."

Another common response of energy being "lost" is exercise. Students feel using energy is losing energy. My strategy is to deconstruct the path of the energy. I use the questions, "Where do you get your energy? Where do your muscles get their energy? Where does your food get its energy? Where does the sun get its energy?" to promote science vocabulary use, I demand the students answer with the word "convert" or "transfer". 

Throughout the entire lesson I introduce the vocabulary necessary to understand the energy being transferred: chemical, mechanical, nuclear, electric, thermal, and radiant. The next part of the lesson will use this vocabulary.  I'm setting the foundation of vocabulary understanding through repetition. My students have been taught my lesson Potential and Kinetic Energy and have some background knowledge of energy transfers. 

I will eventually discuss atomic energy. If a student brings it up early, I explain, "Great idea! Let's talk about that one last. It's special." Before we begin discussing atomic energy, I ask a leading question," How does an atom bomb create energy?" I'm assessing student understanding as well as digging for more information. Finally I can say, "Did you know it was Einstein who discovered that my first statement was really wrong? Does anyone know his mathematical equation?"  Then I define E=MC2  . The lesson was spent teaching the idea of energy transfers. I have convinced students  energy can not be created or destroyed.  My strategy is to teach an outlier concept. Depending upon the class, the students are relieved that they were initially correct. In addition, because they have heard of the formula E=MC2, they now have the Law of Conservation of Energy to associate with the formula to help remember the concepts. 

I end the session with an Exit Slip to assess what information has been learned. I want to find misconceptions and I want to see who may need help later on. 

  1. Name as many types of energy as you can.
  2. If most energy can't be created or destroyed, how is it transferred? Give an example or create a drawing. 

Explain

30 minutes

After the discussion I introduce a demonstration. I have a Hand Crank Generator I crank the generator and it turns on a light. I ask the students to record energies. Many students know light energy because of an electrical unit from 6th grade. I explain that there is also heat energy. "What other types of energy can you think of?" I send a student to the white board to record the energies, heat (thermal) and light (radiant) energy are easy. I ask the students to write the scientific words so we can add them to our word wall. 

I do a couple of jumping jacks and ask if they know the energy. The student who can remember the kinetic energy unit from 7th grade will give the correct answer - mechanical energy. I ask, "How does the energy get from my hand to the light bulb in the hand-crank generator?" We track mechanical energy backwards to chemical energy in the food we eat, to photosynthesis (chemical energy) and finally end up with nuclear energy. In addition, I ask what energy helps to charge a flashlight. Most of my students do not know that batteries are chemical energy. I explain that chemical energy is the energy used to make batteries work because of acid in the battery. 

I complete the generator demonstration again as all students answer in choral responses the transfer of energies. I ask them if they have felt the transfer of energy? Most students admit not.  I review their 6th grade lesson about circuits and ask how we can make a circuit using the wires that come from light bulb to the two screws on the end of the generator. I ask if anyone wants to feel the energy transfer. Student volunteers place their fingers on the end of the generator board. We create a circuit by holding hands and I turn the crank to deliver a little shock. The students know it is coming and are delighted by the zing of the shock. I don't have the capacity to hurt them. If a child wants only to observe, I always allow it. It is a fun way to demonstrate how electricity transfers through each of them and in a circuit. 

You can do a demonstration with different materials. There are generator building kits with many robotic supplies.  To assess understanding, I use an Exit Slip. I have experimented with different questions and decided to let the students decide the question they can best answer. I allow students to choose two questions from a list. 

  1. Explain the Law of Conservation of Energy.  
  2. Explain why energy can't be created. 
  3. Explain why energy can't be destroyed? What is the exception?
  4. Explain the path one of the following energy transfers: Exercise, lightning, light bulbs. Use any demonstration. 

Explore

30 minutes

Before class I fill paper bags with energy transfer "toys". I collect wind-up cars, rubber bands, battery powered flashlights, solar calculators, stuffed animals, balloons, and bouncy balls. I also have energy transfer tools including a generator board, a hand-crank flashlight, matches and a candle, hand warmer, a radiometer, and a Newton's Cradle. 

One of the most effective energy transfer tool is called a bi-metal bar. This is a bar with two different metals. I roll the bar into a loop. When heat is applied, the bar will bend back into a straight line. For some reason unknown to me, this is the demonstration in shich most students say, "Aha!" In student reflections, most students said the bi-metal bar and the generator helped them understand energy transfers. 

My objective is to have Student Led Demonstrations that will give me evidence that my students understand energy transfers. Before I can feel they can be successful, I model what they are going to do. I printed off strips with the 8 types of energy with an icon and some red arrows as a visual for the students. I introduce my lesson with the hand crack generator board. I ask the students, "Which type of energy is being transferred from the light?" We track the thermal and radiant energy back to electrical energy, and then to mechanical energy. I ask students to arrange the energy strips and arrows in the energy transfer. 

I continue demonstrations with each of the energies. I use the hand warmers and lighting a match for chemical energy. I use the live wire, hand crank flashlight, and newton's cradle for mechanical energy. I use a toy truck that when I push it produces a sound and we discuss mechanical energy transferred to electrical and sound energy. When I feel there is a strong understanding of energy transfers, I bring out bags filled with my collections. Inside each bag is a tech deck, a super ball, a wind-up toy, a matchbox car, a rubber band, a solar calculator, and a flashlight. Each table is responsible for creating a demonstration for a fictitious 5th grade class.  I wander around the room to each table to offer formative assessment. Students write their demonstration answers in the Engineering Notebooks. I suggest they use drawings and labels if they think it would help the younger students. Students draw their demonstrations, Law of Conservation of Energy Student Samples.

These physical demonstrations are powerful because the students are engaged in hands-on activities. If you would rather use video instruction, YouTube has great lessons. Check out the Kahn Academy and Bill Nye the Science Guy videos below. 

 

Evaluate

10 minutes

I want the students to take the information they have developed and generalize to engineers. I make a list of common products and ask them to determine the energy transfers. I use an advanced organizer with the following products, Cell Phone, TV, radio, microwave, and ear buds. I introduce the electromagnetic spectrum and explain how the discoveries of its use has led to modern conveniences. I ask my students to come up with a modern invention or innovation and track the energy. 

As groups of my students work together to discuss the modern energy transfers, I listen. Sometimes students have heated arguments about what types of energy are transferred. I think to myself that I hope the students are wrong. It is in their mistakes that the learning takes place. 

My assessment matches my NGSS standard. I am targeting MS-PS3-5 Construct, use, and present arguments to support the claim that when the kinetic energy of an object changes, energy is transferred to or from the object. My reflection assessment question is, "In a one-three sentence summary, describe the demonstration that helped you understand the Law of Conservation of Energy. Construct a picture or use words to explain how kinetic energy is transferred to or from the objects in your favorite demonstration."