Physics: Systems and Applications
 

Teacher's Manual Features
Student Edition

Teacher's Manual

Student Exercise Manual

Links
  • 92 pages, perfect bound
  • Provides an overview of the Unit and strategies for presentation of the topic
  • Gives help on performing the labs, including points to emphasize and tips for set-up
  • Included on the Teacher Component disc as Word files

Below is an excerpt from Unit H of the Teacher's Manual.
Unit H Conservation Laws
Because the laws of conservation of momentum and the conservation of energy are so fundamental to understanding physics, it is strongly recommended that this unit be covered thoroughly in your physics course. 

Summary of Unit H
The unit starts with an examination of inelastic head-on collisions between two free bodies moving in a straight line. Given the masses of the objects, their initial velocities and the coefficient of elasticity, students are encouraged to observe and predict the outcomes of such collisions. It is then shown how the law of conservation of momentum applies to all inelastic collisions and how both momentum and energy are conserved in every elastic collision. The unit continues with a discussion of how potential energy is often converted to kinetic and then reconverted to the original form. The unit concludes by examining the physics of karate and the conservation laws that are involved in this sport. 

Suggestions for Presentation
For the most effective learning, students should be allowed to observe actual collisions in the laboratory and encouraged to contrive simulated collisions with the aid of the computer programs. If computers are unavailable, drawing time-position graphs will help in visualizing the concepts. Learning with graphs is not as fast as it is with the computer, but graphs can be made very quickly. Set an example by making them on the blackboard exactly as you expect the students to make them in their notebooks. Graph paper is not necessary, although a ruler is. The basic outline for a collision diagram is three parallel lines equally spaced with a vertical line going through the center. It helps to make the graph on lined loose leaf paper. The time axis is always the same. A scale, chosen for the horizontal axis. should be carefully measured out with a ruler. 

Center of Mass 
Emphasize that the center of mass of any system never changes its position while any of its particles are colliding. After this concept is developed with observations and diagrams, introduce the algebraic conservation law as a neat, quick way to develop the same answers. Do not spend too much time on the algebraic solution because the algebra does little to increase conceptual understanding of the collision process. 

Momentum and Newton’s Third Law 
Use the action-reaction law, covered earlier, to lead into another useful way of dealing with forces, the impulse concept. Draw students’ attention to the similarity with the work concept. Here is an excellent opportunity for using a computer to study impulses with an analog to digital converter and a strain gauge to measure the force of a collision. 

Elastic Collisions 
Stress that both momentum and kinetic energy are conserved in elastic collisions. Again the time-position diagrams show this very well. However, before introducing conservation of kinetic energy, let the students examine elastic collisions from a conceptual level.

Lab H-1: Elastic Deformation and Speed Change (page 189)
Nature of Lab: Inductive 
This lab is of special interest because the graphs that result are not linear. Because students often experience difficulties with the work-velocity relationship, it is a good idea to use a laboratory exercise to introduce this concept. This lab also provides some practice in dealing with nonlinear relations.

Lab H-2: Energy of a Swinging Pendulum (page 199)
Nature of Lab: Demonstrative Swinging Pendulum 
This is a long lab for which may require 120 minutes of class time. A swinging pendulum illustrates that when potential energy decreases, kinetic energy increases by a corresponding amount. This experiment can also be performed by observing a glider on an air track as it oscillates between the bumpers at the ends of the track.
Try setting up a heavy pendulum attached to the ceiling. This gives better results than small masses swinging from lab stands. The disadvantage is that students may need to take turns to get their ticker tape made. However, the superior results are necessary to be convincing. 
To speed up the rate at which students obtain a ticker tape, mount a roll of paper tape on a stand and allow it to be pulled right off the roll as the pendulum swings. To keep the tape from spilling, sandwich the roll between two cardboard disks. Also, a small amount is friction should be applied to the roll to stop its motion at the end of the pendulum swing. 
Point out that there are a number of other things that can be learned from this experiment. In theory, a frictionless pendulum should swing back and forth forever without any change in its maximum displacement. The velocity curve is a sine curve with a maximum occurring each time that its potential energy is at a minimum. More remarkable, both the kinetic and the potential energy curves also form sine curves with periods that are half as long as those of the displacement and velocity curves.