Prior to this lesson students have built an understanding of what energy is and also know that energy can be transferred.
I begin the lesson today by quickly and briefly eliciting from students what they know and remember about energy. Next, I ask a volunteer to use a hula hoop and see if they can make the hula hoop go around and around their middle. I ask questions like:
What is making the hula hoop go?
Is there a transfer of energy? From what to what?
Is hula hooping kinetic or potential energy? How do you know?
What do you notice about the hula hoop and the way a person moves their body? What happens if someone moves faster or slower?
I explain to students that today we will be experimenting with some simple everyday items to demonstrate energy and motion.
I remind students of the work with the objects from the previous lesson. Next, I show a Dropper Popper. (Dropper Poppers are half of a rubber ball. They typically bounce higher than where you dropped it from! Unlike some objects, a Dropper Popper requires just a small amount of 'activation energy' to work. It is molded into a very special shape that allows it to store elastic potential energy and then convert it to kinetic energy with a POP when dropped from a low height.)
Students work in groups of two for this exploration. I give each group a dropper popper. I show students that when I invert the dropper popper, place it on the table, the dropper popper will eventually invert itself and bounce into the air. I direct students to work together to experiment how they can cause the popper to bounce higher. The only rule for the experiment is that the poppers cannot be THROWN down. I direct students draw a model or sketch of their findings in their science notebooks.
You can see in this photo below a student attempting to turn his "popper" inside out in order to watch it fly into the air.
After most groups have had adequate time exploring and creating a diagram in their science notebooks, I ask student partner volunteers to explain their results. I encourage partners to discuss where the energy for the bounce comes from. (Stored energy from turning the popper inside out.)
I play the first part of this video. (Until about 2:50) I ask students to listen for new words, explanations that help them understand how they dropper popper works, as well as words they already know.
After the video, I lead a brief discussion about new words students heard and their meaning. (elastic potential energy, gravitational potential energy).
I demonstrate how an object will not bounce higher than the point you dropped it from by dropping a bouncy ball. I remind students that we have discussed previously how energy cannot be created or destroyed. I lead a discussion about why the dropper popper bounces higher than where it was dropped.
Background for Teacher to help with discussion from http://coloradoscience.org/
When the popper is “energized,” it gains Elastic (stretchy) Potential Energy. When the popper flips back to its original position, the Elastic Potential Energy is converted to Kinetic Energy and the popper flies into the air. The original Elastic Potential Energy and Gravitational (based on height above ground) Potential Energy of the Popper combine to determine the Total Energy of the popper. This will determine the maximum Kinetic Energy the Popper can gain as it flies upward.
As it moves upward the Popper slows down as its Kinetic Energy is converted back to Gravitational Potential Energy. The whole time the popper is moving its Total Energy remains constant as the types of energy move back and forth between Potential and Kinetic energy. The Dropper-Popper will fly higher than it was released from because when it is dropped it contains Elastic Potential Energy and Gravitational Potential Energy. Both of these are converted to Kinetic Energy as the popper bounces and flies upward – causing the Dropper-Popper to fly higher than it was dropped from, as the Total Energy remains constant. The Ping Pong ball will also fly higher than expected because they are lighter (less mass) than the Dropper Popper.
After discussing how the dropper popper works, students are given opportunity to refine their thoughts and diagrams from earlier. I direct students to use the words elastic potential energy and gravitational potential energy in their diagrams when refining.
Then students have some time to work with the poppers.
You can see a student's science notebook drawing below. I would have also liked to see this student write about kinetic energy and that once the popper begins to move, it is also using kinetic energy.
In this video below, you can listen in as a student explains what she now knows about elastic and gravitational potential energy.
To conclude this lesson, I direct students to make sure they have included the words gravitational potential energy and elastic potential energy on their diagrams. I also direct students to check that they have written about how the dropper popper bounces higher. Students then turn in their notebooks for me to check.
When I check student notebooks, I do not necessarily grade every assignment. I do give feedback to students describing how they can make their work clearer, more precise and accurate.