Unit II: Mechanics
Introduction
This unit should be about six weeks. It should introduce
the students to the concepts of mechanics. Mechanics can be broken down
into linear motion, nonlinear motion, Newton’s laws of motion, momentum,
energy, rotational motion, gravity, and satellite motion. There is an enormous
amount of information within this unit. Demonstrations and experiments
are important facets in understanding all of the concepts packed into mechanics.
Students should become more aware of the mechanics in nature that they
face every day from driving a car to the motion of a satellite.
Intended Learning Outcomes
General Instructional Objectives (and corresponding Specific Learning Outcomes) | Unit Content |
Knows terms
Understands the meaning of terms |
speed, velocity, acceleration, inertia, free fall, momentum, impulse, projectile, mass, weight, force, friction, impulse, angular momentum, work, power, potential and kinetic energy, torque, centripetal and centrifugal force, circular and elliptical orbits, efficiency, equilibrium, spring and neap tide, weightlessness, black hole, big bang, satellite, ellipse |
Understands scientific concepts | motion is relative, velocity is a vector quantity vs. scalar quantity, free fall, elastic vs. inelastic collision, projectile motion, parabola, Newton's Laws, potential vs. kinetic energy, conservation of momentum and energy, center of mass and gravity, Kepler's Laws, law of universal gravitation, inverse-square law, gravitational field, escape speed |
Knows all laboratory procedures
Prepares a plan for an experiment Participates in classroom activities Respects the scientific process Displays a scientific attitude Demonstrates skills in laboratory work |
All content |
Instructional Foci
Experiments: motion with a constant and a nonconstant
velocity, the pendulum, Newton’s second law, work and power, friction;
demonstrations: free fall, and centripetal force; class discussions, quizzes,
homework, readings, questions for thought from The Flying Circus of Physics
by Jearl Walker
Teaching Strategies
For linear motion the teacher should begin with a general description of motion. Speed, velocity, and acceleration should then be introduced. The concept of free fall (acceleration due to gravity, g) can be introduced with a discussion of Galileo and the Leaning Tower of Pisa. Perhaps you could have your own leaning tower experiment by dropping different object from standing on top of the desk. This could then lead to a discussion about Aristotle and his theories in contrast to Galileo Galilei and his theories—noting the public dissatisfaction with Galileo’s leaning tower experiment and Galileo himself.
Nonlinear motion should begin with the concept of relative motion. Then the concept of vectors versus scalars should be introduced, distinguishing velocity as a vector quantity as opposed to speed, which is a scalar quantity. From here the teacher should increase in complexity to projectile motion and circular motion. The space shuttle’s projectile motion could be explored to make the concept relevant to the student, expanding on what they are already familiar with.
Building on the information presented in linear and nonlinear motion, the teacher should explore Newton’s Laws of Motion. Many in class demonstrations and discussions should be utilized to ensure students understand the concepts presented here. The difference between mass and weight should be discussed. Force, inertia, and the conservation of energy are other key element to be taught in this section, also.
Next, the idea of combining inertia and motion to get momentum should be introduced. To produce a change in momentum either the velocity or the mass must be manipulated. Most commonly the velocity is changed due to a force acting on the object for a given time which is know as an impulse. Impulses such as the brakes of a car, the swing of a golf club or baseball bat, or the bouncing of a ball can all be discussed and demonstrated. The conservation of momentum should then be presented by discussing collisions—both elastic and inelastic—using examples of cars and billiard balls as common examples.
Then we begin the study of energy. Energy is difficult to define because it is a "thing" as well as a process. Everything has energy, but we only observe it when it as it is being transformed. In other words, we see it in forms—in the form of the food we eat, in the form of electromagnetic waves we feel as heat from the sun, in the form of photosynthesis for plants, etc… These aspects of energy should be introduced before exploring related concepts, like work. Mechanical energy, such as potential and kinetic energy should then be compared and contrasted. Of course one of the fundamentals of physics, the concept of the conservation of energy, should then be taught, giving examples of how cars consume more fuel when the air conditioner, lights, and radio are on—nothing is free. Then the teacher can discuss energy used for machines and energy used for life—what are the similarities and differences?
There is much more to nonlinear motion and Newton’s Laws than previously discussed. Rotational motion builds on these principles to explain the rotation of an object about an axis. The teacher should discuss rotational inertia and how torque effects that inertia. The center of mass and center of gravity as well as centripetal and centrifugal force should be demonstrated. The classic demonstration of a bucket full of water rotating around your arm (swinging it) is ideal in demonstrating centripetal and centrifugal force. And of course the exploration of this section should end with a discussion of the conservation of angular momentum.
To introduce this section on gravity the teacher should discuss Johannes Kepler and Kepler’s laws of planetary motion. He/she should then go on to discuss Newton’s law of universal gravitation. Then weight and weightlessness could be introduced with a discussion on taking a scale into an elevator (what does the scale read when stationary, when moving, and when free falling) and astronauts. Following this, the ocean tides should be explained. Gravitational fields and black holes should be taught as a precursor to the next section on satellite motion.
Current satellites—their forms and functions—should be
presented as an introduction to the final section of mechanics (at last!),
satellite motion. Newton’s ideas of the falling apple and "falling moon"
should be studied. Basic satellite motion and escape speed should also
be explored. Finally, what would a section of mechanics be without a discussion
of energy conservation and satellite motion?
Special Notes
1. All labs should be preceded by an in class demonstration by the teacher of the proper procedures. After viewing the demonstration, students’ homework should be to prepare a plan for the experiment. Due to the time constraints of high school classes it is imperative that students have thought through the experiment before class. You, the teacher, need to know that they are aware of proper equipment set-up and safety precautions as well as appropriate hypothesis development, variable controls, and observation and measurement procedures.
2. Labs can be found in Laboratory Manual in Conceptual Physics by Bill Tillery.
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