WEP - Introduction to Work, Energy, and Power

Work, Energy, and Power Overview

Introduction

The prominent 20th century physicist, Richard Feynman, said "It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount." Nevertheless, the mathematical model for the relationships between work and energy serve to model physical problems and, more importantly, predict natural and man-made phenomena. The relationships that we discover in this unit provide a powerful analytical and design tool for problems that would otherwise be difficult or impossible to solve.

Essential Questions

1. What is the difference between a conservative force and a non-conservative force?
2. What is kinetic energy?
3. What is work?
4. Why is the cosine function used in the definition of work?
5. What is the difference between work and net work?
6. Are work and energy vector quantities or scalar quantities?
7. What is the relationship between work and kinetic energy?
8. What is the physical meaning of negative work in terms of acceleration?
9. What is the rate of change of doing work with respect to time?
10. What is the rate of changing kinetic energy with respect to time?
11. Since gravitational potential energy is mgh only near the surface of the earth, how is gravitational potential energy calculated when this assumption is violated?
12. How can the principle of conservation of energy be used far from the surface of a planet?
13. How is escape velocity calculated?

Key Terms

1. conservation force - Work done by a conservative force on an object to move it from point A to point B is independent of the path from A to B.  Alternatively, the work done by a conservative force to move an object from point A back to point A is zero.
2. energy - A conserved property of a physical system, which cannot be observed directly but can be calculated from its state.
3. Joule - Symbol J, is a derived unit of energy or work in the International System of Units. It is equal to the energy expended (or work done) in applying a force of one Newton through a distance of one meter (1 Newton meter or N•m), or in passing an electric current of one ampere through a resistance of one ohm for one second.
4. kinetic energy - The energy that an object possesses due to its motion.
5. net work - The scalar addition of the work done by each individual force moving an object through a displacement.
6. non-conservative force - Work done by a non-conservative force on an object to move it from point A to point B depends on the path taken from A to B.
7. power - The rate of doing work per time or the rate of change in kinetic per time.
8. work - A physical quantity described by the product of force in the direction of motion, times the displacement of the moving object.
9. equipotential - a region in space where every point in it is at the same potential equivalent to a region of space where a given mass has a constant potential energy.
10. gravitational potential energy () - potential energy associated with the gravitational force, equal and opposite to the work required to elevate mass against a planet's  gravity.
11. gravitational potential (V) - gravitational potential energy per unit mass.

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