Introduction to Work and Energy: The Hopper Popper Surprise
This activity has benefited from input through a review and suggestion process.
This activity has benefited from input from faculty educators beyond the author through a review and suggestion process as a part of an activity development workshop. Workshop participants were provided with a set of criteria against which they evaluated each others' activities. For information about the criteria used for this review, see http://serc.carleton.edu/sp/compadre/devactivities/reviewcriteria.html.
This page first made public: Apr 27, 2010
This material is replicated on a number of sites as part of the SERC Pedagogic Service Project
This activity is designed to provide qualitative understanding of the Work-Energy Theorem. Students are expected to have read introductory material regarding the theorem, and are tested on this with a short online quiz prior to class. After a brief discussion a "warm-up" demonstration is conducted with student participation. A question is then posed regarding the height a "Hopper Popper" will reach if launched from a thumb instead of a hard flat surface. After initial responses are presented, discussion groups are formed to achieve consensus and provide justification of conclusions. This is followed by a confirming demonstration with surprising results.
Context for Use
Setting: High school or college, all class sizes. This in an Interactive Lecture Demonstration classroom activity.
Time required: 15 to 20 minutes.
Special equipment: Marshmallow blow guns, overhead or lcd projector, audience response system, Hopper Poppers.
Pre-requisite knowledge: Forces, Newton's Laws, work, kinetic and potential energy, and introductory reading on the Work-Energy Theorem.
Description and Teaching Materials
If students do not demonstrate understanding on the reading quiz that positive work will increase the kinetic energy of an object, additional time must be spent on the definition of work. Examples drawn from earlier discussions on Newton's Second Law, recast in terms of work and energy will help. Specifically, emphasize that positive work results in positive acceleration and an increase in speed, and thus kinetic energy, and that negative work results in negative acceleration (deceleration) and a decrease in speed and kinetic energy.
If students do not demonstrate understanding that an increase in the distance over which a force is applied will increase the change in kinetic energy or speed of an object, the Marshmallow Blow Gun demonstration and/or additional Newton's Second Law examples recast in terms of work and energy will be helpful.
If students show significant grasp of the Work-Energy Theorm, go straight to the Hopper Popper Surprise interactive demonstration. If there is some confusion, the Hill and Haystack concept test question and discussion prior to the demo may help. For either, pose the question as a peer instruction activity, preferably with an audience response system. Have each student answer individually, then divide the class into discussion groups to arrive at a consensus. Have each group present their answer and reasoning. Follow this with a second polling of the question and discussion prior to actually doing the demonstration.
Teaching Notes and Tips
After the Hopper Popper Surprise demo, a launch of the popper from hard surfaces both concave and convex will help students understand the behavior of the popper, as will attempting to launch it from your fist with a quarter-sized opening below the center of the popper.
A follow-up lab using fan carts or may be useful.