Lesson 4: A look at mechanical energy

Title: A look at mechanical energy

Author: Andrew Stillman

Week: 3

Unit/Lesson Plan #: 5

Unit theme: Materials, Tools, and Machines

Textbook references: N/A

Learning objectives:

• Students will define their systems in such a way as to internally account for all energy transfers.
• Students will learn to apply a pie chart energy analysis to a variety of simple mechanical situations.
• Students will apply energy analysis to the three types of catapults: torsional, bow/spring, lever/gravity.

Key Questions, Concepts, or Themes:

• Mechanical energy is the ability to do physical work, which is to push or pull something over some distance, often causing acceleration (change in velocity).
• Energy can exist in many forms, and is often transferred from one form to another.
• When mechanical energy is stored in gravitational field between two objects, it is called gravitational potential energy.
• When mechanical energy is stored in the stretch of an elastic material, it is called elastic potential energy. Elasticity can longitudinal or torsional.
• When mechanical energy is tranferred into the movement of a massive object, it is called kinetic energy.
• When mechanical energy is transferred to the jiggling of particles due to the rubbing of surfaces or the deformity of a material, it becomes thermal energy.
• The total amount of energy is always conserved in a system defined in such a way as to internally account for all energy transfers.

Stage 1:

Introduce a wind-up toy to the class. Ask where it's energy comes from. What did I have to do to give the toy energy. Before I let go of the toy, where was the energy? What happened to the energy once the toy was released? Where did the energy go once the toy was stopped at the end?

Introduce the idea of the system, the energy flow diagram, as well as the bar charts to show different kinds of energy. Don't introduce formal names for different form of energy yet...just define it in terms of the "thing" that represents where the energy is stored or obserable. (Energy stored in the person's muscle cells, energy stored in the spring, energy in the motion of the toy, energy stored in the room's temperature increase)

Stage 2:

Quickly define gravitational potential, elastic potential, thermal, and kinetic forms of energy.

Give some other simple scenarios in the form of diagrams that include before, during, after, or sequences of phases in an event. Have students whiteboard and present their solutions to the class.

Stage 3:

Have students analyze different styles of catapult using the same energy analysis tools.

Homework: (attach/link digital resources):

To do: create simple energy transfer scenario worksheet

Assessments: (attach/link copies)

__ Group assessment

__ Observation of process/student work

__ Self-assessment by student

__ Teacher generated assignment

__ Written project

__ Test/Quiz

__ Other: ____________________________________