Conservation of Energy & Energy Transfer

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SWBAT explain that energy is neither created or destroyed but transformed and accounted for.

Big Idea

What happens when friction is added to the skate park?

The Need for the Lesson

The word energy is used in many different contexts in the English language. We say, for example, we do not have enough energy to run a race or we will run out of energy soon. In physics, energy is the capacity to do work, it cannot be created or destroyed but it can change. Many middle school students still harbor the belief that energy can be created and/or destroyed. How we use the word energy in everyday language can cause students to develop misconceptions in physical science. One common misconception among students is that motion energy cannot be transferred to thermal energy. Adding friction to the skate park shows students how kinetic energy decreases and thermal energy increases.

The PhET Simulations are ideal for student exploration. This lesson has guided questions to encourage exploration to counter student misconceptions. Students will see that the when the friction is increased at the skate park there is an increase in thermal energy.

The PhET Simulations are designed specifically for student inquiry. Students can change variables in their explorations creating models that can be used to represent systems and their interactions - in this case how energy flows withing a system.

Additionally students explore the DCI (Disciplinary Core Idea) that when the motion of an object changes there is inevitably some other change in energy at the same time.

Simulations can be a rich source for student inquiry.

Investigation Summary & Preparation

5 minutes

Students will use the PhET simulation - Energy Skate Park - as a model to explore the total energ in the system by changing variables. In this case they will be observing the total energy of the system, with no added friction, they with added friction. (MS-PS3-2 Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system) In this lesson students will change the friction in the skate park causing energy to be transfer from kinetic energy to thermal energy. Students will observe that the kinetic energy is not lost but transferred. (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.)

The simulation include options to view graphs supporting the CCSS ELA standard integrating visuals to clarify understanding and provide evidence to support student claims (SL.8.5 Integrate multimedia and visual displays into presentations to clarify information, strengthen claims and evidence, and add interest.)

Student engagement is supported as students use the Energy Skate Park simulation as a model to explain the concepts of potential, kinetic energy and thermal energy. Students are also developing perseverance as they extract evidence through inquiry to support their understanding of energy transfer. By changing variables to deepen their understanding, students are developing mastery as they use the simulation as an iterative process. (SP2 - Using Models)

Conducting investigations is inherent in all the PhET simulations as they allow for the change of variables that allow students to make changes in their investigation that lead to the discovery of answers to specific questions. Students in this simulation are changing variables in the simulation to understand the relationship between kinetic energy and thermal energy. (SP3 - Planning and Conducting Investigations)

Throughout their investigations students are asked to collect observations and use the information collected to make conclusions building upon their experiences to develop habits and skills leading towards independent explorations. The lesson asks students to collection observations in a table and use that information to state conclusions about their investigation. (SP8 - Collecting and Communicating Information)

At the end of the lesson, students will experiment with pullback toy cars; comparing potential and kinetic energy using toys.

A complete material list can be found in the resource section.

Students in Action

30 minutes

Students in Action

I start with a review of terms from the previous lesson - Exploring the Relationship between Potential & Kinetic Energy. 

We explored the energy transfer from kinetic energy to potential energy at the skate park. When did the skateboarder have the most potential energy? At the top of the ramp. Was the skateboarder moving when he had the most potential energy? No. How would you define potential energy? Potential energy is stored energy. Let's add to that definition. We said that he has the most potential energy at the top of the ramp. Does he have the same potential energy when he is at the bottom of the ramp? No. Does his position determine the amount of potential energy? Yes. So potential energy is stored energy created by the position of the object.

What is kinetic energy? The energy of motion. As the potential energy of the skate boarder decreased what did you notice about the kinetic energy? It increased. Did the total amount of energy in the system - the skateboard park - change? No. What can we say about the relationship between potential and kinetic energy in the skate park? When one type of energy goes up the other goes down and the energy remains the same in the system.

Today we will look at another type of energy transfer. Very quickly rub your hands together. What kind of energy did you observe as you rubbed your hands together? Kinetic energy or the energy of motion. What was the result of rubbing your hands together quickly? The hands felt warmer. Why? We created friction by rubbing our hands together. The warmth you experience is call thermal energy. We call the energy of heat thermal energy. Where did the thermal energy come from? Rubbing our hands together. What is the relationship between the energy of motion when friction is added and thermal energy? When friction is added to kinetic energy some of the energy of motion is changed to thermal energy.

I give students a few minutes to answer questions 1, 2, 3 & 4 with their elbow partner. The strategy is Turn/Talk/Record. Students are discussing the questions together and being help accountable for their discussion by recording their answers. Before going to the website, I ask students to share out their answers to questions 1, 2, 3 & 4. This is a mini formative assessment to see if students need more support to build adequate background knowledge before continuing to independently explore the simulation. Middle school students bring a wide range of background knowledge from elementary school so this step is a helpful probe to check for understanding.

Link to Energy Skate Park Simulation

We use the HTML5 version of the simulation. This format works on both PCs and IOS devices. It also does not require a download so we do not have to work about problems downloading a Java version.

In this short video, I share how I prepare the students to begin using the simulation and take a brief look at completed student work and expected observations.

As students work through the lesson, I circulate through the classroom to be sure the settings are correct and they are collecting the appropriate observations and using evidence from these observations to support their conclusions. 

Connecting the Learning

15 minutes

We have a brief class discussion about student findings. I want to make sure that students understand that energy is conserved in both systems - without added friction and with added friction - even though the friction system now has thermal energy. The thermal energy is part of the total energy in the system.

What did you notice about the total energy in the system with no added friction? It stayed the same.

What did you notice about the total energy in the system with added friction? It also stayed the same.

When there is added friction, what type of energy do we have that was not present without added friction? Thermal energy.

What happened to the potential and the kinetic energy as the thermal energy increased? The potential and kinetic energy decreased and the skate boarder slowed down.

Did the addition of thermal energy change the total energy in the system? No.

What caused the thermal energy to be part of the system? Friction, because friction is an opposing force.

What does the simulation tell us about conservation of energy? The total energy always stays the same. 

I hand out toy cars, track, foil, wax paper and newspaper for student exploration. How does changing the surface, change the movement of the toy car?

Students explore how changing the amount of friction changes the amount of kinetic energy in these toy cars.

Connecting a virtual experience with a hands-on activity helps reinforce learning. In the next lesson Potential & Kinetic Energy Experimental Design, students will be working formally as scientists to explore changing surfaces to change friction.

Today's exploration allows students to play with the materials. It is often surprising to me that students have little experience learning by playing. Providing the opportunity to play ahead of the formal data gathering experience allows students to build some background information about how the systems work.