by: Tami O’Connor
One of the units I enjoyed most as a middle school teacher was the section on energy. The many awesome hands-on experiments generated such a series of oohs and aahs that it made my already-enjoyable days even more enjoyable! One of my favorites was a lesson that dealt with the Law of Conservation of Energy. A consequence of this law is that energy cannot be created, nor can it be destroyed. (The students would have already explored potential and kinetic energy before the following activity.)
I initiated this lesson reviewing what happens with energy in a closed system. The students clearly remembered comparing the amount of potential energy to kinetic energy using the example that the height of a roller coaster’s first hill is always greater than the height of any of the remaining hills. It is, of course, possible to have a little hill followed by a higher hill as long as the roller coaster is going faster at the top of the little hill than the next higher one. The students were generally able to explain the transfer of energy including heat energy and sound energy in the overall system.
I would then take out a normal playground ball and a meter stick and ask the the students to predict the height the ball would bounce if dropped from a meter off the ground. Most students accurately predicted that the ball would not bounce as high as the height at which it was initially dropped. Of course, we would then test our hypothesis. A few students in each class would always insist that the ball could bounce higher than the height at which it was dropped, so I would invite them to show me how it could happen. Inevitably, the student would add energy to the system by throwing the ball down to the ground rather than simply dropping it. This was a great opportunity for discussion and was a topic that we would tap into later in the lesson.
I would then pull out my complete collection of balls that ranged from the hard, less bouncy baseballs to the rubber and highly bouncy super balls and have the students explore on their own. Though there were noticeable differences in the elasticity of the balls in my collection, none of them bounced higher than the height at which they were dropped.
My next demonstration utilized a racquetball that I had cut in half… well, actually a little less than half. I would again ask my students to predict how high the half-ball would bounce. The answers varied, but by this time, not one student predicted that it would bounce higher than its drop point. As before, we tested their hypotheses before moving on to the next step.
Because the racquetball is very flexible, I was able to turn the half-ball inside out thus storing elastic potential energy. Once again, I asked the students to predict what would happen when I dropped the ball. Based on their recent experience, they all answered that the half-ball would bounce lower than its drop point. Of course, because I stored elastic potential energy in this system, once the half-ball hit the ground, it popped right side out and was propelled significantly higher than the point at which it was dropped. Talk about a discrepant event!
Thank goodness Educational Innovations sells Dropper Poppers. This product eliminates the time and difficulty of cutting racquetballs in half, not to mention the expense of purchasing racquetballs really intended for use in the court!
Dropper Popper Activities
When this small, “half-ball” is turned inside out and then dropped onto a hard, flat surface, it releases the stored energy and “jumps” higher than the point from which it was released.
EXPLANATION
• Elastic potential energy is energy that is stored as a result of deformation of an elastic object such as a spring or a rubber band.
• Gravitational potential energy is energy that is stored as a result of an object’s position above the ground.
ACTIVITY #1 How High Will a Ball Bounce
Showing your students a regular ball such as a small super ball, basketball, or ping pong ball, survey the class to determine the height at which they predict the ball will bounce if dropped without additional energy. You may be surprised to learn that some students will predict that the ball will bounce higher than the point from which you drop it.
Drop the ball. Students will discover that the ball will never reach the height from which you dropped it. The Law of Conservation of Energy states that energy cannot be created nor destroyed; it can only be transferred as alternate forms of energy. The energy that initially went into the system was transferred out as sound energy and heat energy. The ball will never bounce higher than the initial drop point because the energy that comes out of a system can never exceed the energy that goes in.
Explain to your students that the ball’s energy was stored due to its position above the ground. Because of the force due to gravity, the ball falls down as it is attracted to the earth.
ACTIVITY #2 The Dropper Popper
Show your students the Dropper Popper (POP-100), and ask them to predict the height at which the popper will bounce if you drop it straight down. Drop the popper without turning it inside out and observe the height at which it returns.
Turn the Dropper Popper inside out and explain that by doing work on the popper you are storing energy in it. Have the class predict again the return height of the popper after it is dropped. Drop the popper with the “bulge” pointing upward. When the popper hits the ground the stored elastic energy will be released and will cause the popper to bounce higher than the point from which it was dropped.
ACTIVITY #3 Ping-Pong Ball
Be sure all students wear protective eye wear.
This activity is truly best when each student has his/her own Dropper Popper and a Ping-Pong Ball, (PNG-100). Have the students store energy in the popper by turning it inside out. Then place the ping-pong ball in the “bowl” of the popper. Drop the popper onto a hard surface in such a way that the ping-pong ball remains above the popper and inside of its “bowl”. The bulge should be on the bottom of the popper so the ping-pong ball fits securely inside. The height your ping-pong ball will fly will be truly impressive!
• Have students estimate how high the ball travels.
• Change the height at which you drop the popper and determine if the height the ping-pong ball travels is based more on gravitational or elastic potential energy.
An additional demonstration of the Law of Conservation of Momentum and Energy can be shown using the AstroBlaster (SS-150). This device has several balls threaded on a plastic shaft. When dropped straight downward onto a hard surface, the top ball can rebound to a height equal to five times the original drop!
This entry was posted on Wednesday, December 30th, 2009 at 6:01 pm and is filed under energy, experiments, Middle School level, Physics.You can follow any responses to this entry through the RSS 2.0 feed.You can leave a response, or trackback from your own site.
As a physics enthusiast with a deep understanding of energy concepts, I find Tami O'Connor's article on energy-related experiments in middle school captivating. The hands-on activities described not only engage students but also effectively demonstrate fundamental principles such as the Law of Conservation of Energy. My expertise in physics allows me to elaborate on the concepts covered in the article and provide additional insights.
Law of Conservation of Energy: The Law of Conservation of Energy is a fundamental principle in physics, stating that the total energy in an isolated system remains constant over time. Energy can neither be created nor destroyed, only transferred or converted from one form to another. Tami's article brilliantly incorporates this law into the lesson by discussing potential and kinetic energy in the context of a roller coaster and later applying it to the ball-drop experiment.
Potential and Kinetic Energy: Potential energy is stored energy based on an object's position or condition, while kinetic energy is the energy of motion. In the roller coaster example, potential energy is higher at the top of the first hill due to elevation, converting to kinetic energy as the coaster descends. This dynamic interplay is crucial in understanding the subsequent experiments involving the playground ball.
Elastic Potential Energy: The article introduces the concept of elastic potential energy, which is stored energy resulting from the deformation of an elastic object, such as a racquetball or a Dropper Popper. By turning the racquetball inside out, Tami demonstrates the storage of elastic potential energy, a captivating example of energy transformation.
Gravitational Potential Energy: Gravitational potential energy is stored energy due to an object's position above the ground. In the experiments, especially with the regular ball and the Dropper Popper, the height from which an object is dropped influences its potential energy. Tami effectively connects this concept to the force of gravity, explaining why the ball falls as it is attracted to the Earth.
Dropper Popper: The Dropper Popper is a fascinating tool that simplifies the demonstration of elastic potential energy. By turning it inside out, storing energy, and then releasing it upon impact, the Dropper Popper showcases the conversion of potential energy into kinetic energy, resulting in a bounce higher than the initial drop point.
Ping-Pong Ball Experiment: The Ping-Pong ball experiment extends the concept of elastic potential energy. By placing the ball in the Dropper Popper and dropping it onto a hard surface, students observe an impressive display of energy transfer. This experiment not only reinforces the concept but also allows students to estimate the height the ball travels, promoting engagement and critical thinking.
In summary, Tami O'Connor's article masterfully intertwines practical experiments with essential physics concepts, making the learning experience enjoyable and insightful. The incorporation of real-world examples and hands-on activities aligns with best practices in science education, ensuring that students grasp the principles of energy and conservation through experiential learning.
