Second Grade: Unit 3 Mechanical Energy. mechanical energy potential energy kinetic energy

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1 Second Grade: Unit 3 Mechanical mechanical energy potential energy kinetic energy Background Information for the Teacher: is the ability to do work. Work is the force a system produces on another system over a distance. Work is done when a force acts on an object to cause it to move, change shape, displace, or do something physical. Therefore, energy is equal to the ability of a system to pull or push against other forces. In all instances in which work is done, there is an object which supplies the force in order to do the work. In the process of doing work, the objects doing the work exchange energy in one form to do work on another object to give it energy. The energy acquired by the objects upon which work is done is known as mechanical energy. If a student picks up a book and places it on a desk, the student supplies the force to do the work on the book. The book now has the mechanical energy transferred by the student lifting it. If a pitcher winds up and throws a baseball towards home plate, then the pitcher supplies the force to do the work on the baseball and the baseball has the mechanical energy from the force put upon it by the pitcher. If a barbell is lifted from ground level to a height above a weightlifter's head, then the weightlifter is supplying a force to do work on the barbell. The weightlifter has transferred mechanical energy to the barbell. An object which possesses mechanical energy is able to do work. In fact, mechanical energy is often defined as the ability to do work. Any object which possesses mechanical energy whether it is in the form of potential energy or kinetic energy is able to do work. That is, its mechanical energy enables that object to apply a force to another object in order to cause it to be moved. Mechanical energy is the sum of all of the kinetic and potential energy in an object that is used to do work. In other words, it is energy in an object due to its motion or position, or both. Consider someone pushing on a door to open it. The person pushing on the door possesses potential chemical energy, energy stored in the body, and when the hands are lifted to push the door, the action also has kinetic energy (energy in the motion of the hands). By pushing the door, the person s potential and kinetic energy is transferred into mechanical energy, which caused work to be done (door opened). Here, the door gained mechanical energy, which caused the door to be displaced temporarily. For work to be done, an object has to supply a force for another object to be moved. Mechanical energy can be broken into two forms of energy: kinetic energy and potential energy. Kinetic

2 Kinetic energy is the energy of objects in motion. These include very large things, like planets, and very small ones, like atoms. The heavier a thing is, and the faster it moves, the more kinetic energy it has. If a large ball and a small ball are resting on a table, they both have potential energy, or the energy of resting objects. If a force is applied, both balls will fall off the table, converting the potential energy to kinetic energy. Because the large ball has more mass, it will fall with greater force, meaning it has more kinetic energy than the smaller ball. Kinetic energy can be transferred to other objects. When a ceiling fan is turned on, the kinetic energy of the moving fan blades is transferred to the air, causing air molecules to move faster, creating a breeze. Some of the many forms of kinetic energy include rotation, vibration, and movement from one location to another. Potential Potential energy is the energy stored in an object depending on its position. In this form, the energy is not doing work, but it has the potential to be converted to other energy forms. In the case of mechanical energy, potential energy transforms into kinetic energy when the object is set into motion. Two forms of potential energy are gravitational, the energy of an object depending on its height above the Earth s surface, and elastic potential energy. Elastic potential energy is the energy stored in an object that is stretched or compressed, like a spring. A car parked in a driveway has potential energy. When the ignition is started and it drives away, the car gains kinetic energy as it moves. The food that we eat is broken down and stored as potential energy until we begin to move and convert the potential chemical energy into kinetic energy. Total Amount of Mechanical The mechanical energy of a system is the sum of the kinetic and potential energy within the system: mechanical energy = potential energy + kinetic energy. The result of this equation is called the total mechanical energy. Mechanical energy is measured in units called joules. Objects with mechanical energy are either in motion or have stored energy to do work. While an isolated system conserved its mechanical energy, this doesn't typically happen in the real word because some potential energy is transformed into other forms of energy, such as heat, through air resistance and friction. This energy becomes "lost" to the system.

3 Activity 1: Ask students to look at the following pictures. Encourage students to describe each picture. What does the light bulb signify? As the students are discussing the pictures, record their dictation, making sure the students can clearly see what you are writing. Copy what they say word for word; do not rephrase anything that they say. After the discussion has covered the pictures, ask how the pictures might go together to make a story. Who might have an idea? What do you think the idea is about? As students answer the questions, begin to develop their discussion into a story format. Ask students to imagine what the characters might be like, who else might be in the story (but isn t shown), and how the events of the story

4 might sequence. Allow the students to add to the story, prompting them with sequence and possible events. Once the story is completed, read it to the students in entirety. After modeling fluency, have them read the text orally and silently. This will help them develop fluency.

5 Activity 2: Student Handouts 1 and 2 Tell students they are going to learn about two kinds of energy, potential and kinetic. Show students the two charts below. Discuss what each section of the chart is asking students to complete. Once students are clear on the information they will be looking for, watch the video below. What is it? Where does it come from? Potential What are some examples? How does it look?

6 What is it? Where does it come from? Kinetic What are some examples? What does it look like? Have students complete the charts on Potential and Kinetic energy. Replay the video if necessary to help clarify and extend answers.

7 Activity 3: Student Handout 3 Ask students to look at the chart below. (this is a partial chart. See Student Handout for complete list of objects.) Explain that as they watch the following video, they will look at each object listed on the chart. They will decide if the object begins with potential energy or kinetic energy. Put an X in the column under Potential if the object appears stopped or at rest. Put an X in the Kinetic column if the object is moving. Many objects will begin as one form of energy and transfer to the other form. For example, if the Roadrunner appears moving, put an X in the Kinetic column. If he stops moving, he has transferred Kinetic to Potential, so then put an X in the Potential column. Object Potential Kinetic Roadrunner Wiley E Coyote Wooden pole Rocket #1 Roadrunner Cartoon video: %20&qs=n&form=QBVR&pq=videos%20of%20the%20road%20runner%20&sc=1 26&sp= 1&sk=#view=detail&mid=AD76230D832D AD76230D832D When students have completed their charts, discuss how objects transferred from potential to kinetic energy or kinetic to potential energy. What had to happen for energy to transfer? What was the force used to move or stop objects from moving? How many times did objects transfer energy? Were most objects using kinetic energy or potential energy? What type of energy did the Roadrunner use the most? What about Wiley Coyote?

8 Activity 4: Reread the story the students created in Activity 1. As it is being read, encourage students to discuss when potential energy is being used and when kinetic energy is being used. Record each event in the story and determine the energy being used in each. Discuss when and how the energy transfers to potential or kinetic energy. Help students make connections between a force being used and the energy it transfers. Introduce the concept of mechanical energy by telling students that all of the kinetic energy and all of the potential energy in an event in the story is the amount of mechanical energy being used. Show students this formula: Kinetic energy + Potential energy = Mechanical

9 Activity 5: Student Handout 4 Using the story created in Activity 1, ask students to complete the Vocabulary Diagram. They should record examples and illustrations from the story. Have students use their own words/ideas to complete the Diagram. Draw a picture of potential energy here. Draw a picture of kinetic energy here. Mechanical Write a paragraph about potential and kinetic energy here. Write a definition of mechanical energy here.

10 Student Handout 1 What is it? Where does it come from? Potential What are some examples? How does it look?

11 Student Handout 2 What is it? Where does it come from? Kinetic What are some examples? How does it look?

12 Student Handout 3 Object Potential Kinetic Object Roadrunner Rocket #2 Wiley E Coyote Frisbee Cloud Firecracker Exclamation Cactus mark Wooden pole Rocket #3 Potential Kinetic Rocket #1 Rocket holder #1 Giant fly paper Fly Safe Rocket #4 Rope Cliff Rock Tennis ball

13 Student Handout 4 Draw a picture of potential energy here. Draw a picture of kinetic energy here. Mechanical Write a paragraph about potential and kinetic energy here. Write a definition of mechanical energy here.