Mechanical Energy

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Objective

SWBAT explain the difference between potential and kinetic energy and provide examples of each.

Big Idea

Understanding the basics of mechanical energy is essential to understanding its relationship with mass and position.

Engage

5 minutes

This lesson introduces students to mechanical energy as potential and kinetic. Students have been exposed to the idea of mechanical energy in the previous lessons about Forms of Energy.  This lesson addresses the foundational principles of MS-PS3-5, in that students need to know what potential and kinetic energy are in order to identify the energy transfers between them.

For the first part of this lesson, students recall what mechanical energy is (energy or motion or position) and provide an example.  They will write the answer to this question in their student notes sheet or in their notebooks. 

After 3-4 minutes, I choose one student to share their answer to the whole class.  I write it on the whiteboard as a reminder. 

Explore

5 minutes

Now, I ask the students to imagine what would happen if I were to drop a raw egg onto the classroom floor. Why? (I am holding a raw egg in my hands while asking this question. Later, I will drop it.) Students write their responses in their notes sheet. 

I am looking for students to identify that the egg will, indeed, fall and break because of gravity and because the shell isn't strong enough to withstand the pressure of falling. 

After about 4 minutes, I ask a few students to read their responses aloud to the whole class. 

Sample Responses (for an explanation on why this works, see reflection below)

Explain

10 minutes

After hearing the responses, I drop the egg into a plasticware container on the desk. It cracks. Now, we have a discussion about their predictions.  Were they correct? (Most of the time, yes.) 

I ask the following questions aloud, telling students I want them to think quietly to themselves: 

What force pulled the egg to the ground? (Gravity)

What kind of energy does the egg have? (Mechanical)

Where did the egg get the energy to fall? (From my hand moving it upwards.)

After we discuss these questions, I draw the egg scenario on the whiteboard, labeling where it has potential energy and where it has kinetic.  

I ask the students to define the words "potential, kinetic, gravity and mass" in their notes sheet using the diagram and what they know about mechanical energy to help them.

After about 6-7 minutes, we share our responses as a class and make sure they're correctly written in our notebooks. 

Elaborate

10 minutes

Now students look at 5 different picture examples of mechanical energy and decide if each one is an example of potential or kinetic energy and provide justification for their choice. 

They should notice how some images appear to be moving (kinetic energy) and some appear to be stationary (potential). 

The Elaborate Student Sample seen here shows that the student identifies kinetic energy with something that's moving. This is acceptable for this lesson, as they are understanding that something with potential could move, but isn't. 

Evaluate

5 minutes

Students reflect on what they've learned in this lesson by answering the following question in their notes sheet: 

Explain what happened when I dropped the egg on the floor in terms of kinetic and potential energy.

Here, I am looking for an explanation that includes when the egg had potential energy (when I was holding it, before I dropped it), when the egg had kinetic energy (when I released it from my hand) and what caused it to fall (gravity) and where the energy to fall came from (my hand pulling it up to the release point).