# Physlet^{®} Physics 3E: Mechanics

## Chapter 1: Introduction to Physlets

This chapter is an introduction to the various types of interactive curricular material you will find in *Physlet ^{®} Physics 3E*. In addition, this chapter gives a brief tutorial on the types of basic computer skills you will need to run, interact with, and complete the exercises.

## Chapter 2: One-dimensional Kinematics

Motion along a straight line, also called one-dimensional motion, can be represented in a number of different ways: as a formula, as a graph, as data in a table, or as an animation. All four representations are useful for problem solving.

The study of motion in one, two, or three dimensions is called kinematics. What distinguishes kinematics from the techniques which we will consider later is that, at the moment, we do not care **why **an object is moving the way it is. We just care **that** it is moving the way described. Do not think that this degrades the study of kinematics. The exact opposite is true. Kinematics is powerful precisely because it is independent of the cause of the motion. We will learn to speak using the common language for describing motion irrespective of the cause.

## Chapter 3: Two-Dimensional Kinematics

In this chapter we generalize the study of motion in one dimension to the motion of objects in two dimensions. In doing so we discuss two of the most important forms of two-dimensional motion, projectile motion and circular motion.

## Chapter 4: Newton's Laws

We have just finished our study of kinematics. In kinematics we did not care **why** an object was moving. We are now going to explain why objects move or do not move. We do so by using the concept of force. In this chapter we consider the basic techniques of free-body diagrams, the normal force, and the forces of weight and tension.

## Chapter 5: Newton's Laws 2

We have thus far studied simple Newton's laws problems and now consider additional applications such as friction (including air friction), circular motion, and springs.

## Chapter 6: Work

In this chapter we will talk about the concept of work. The concept of work has a very special meaning to physicists and differs from the colloquial usage in a number of ways. Work is related to the displacement through which the force acts. We will consider forces and displacement in the same direction and also consider what happens when the force and displacement are not in the same direction.

## Chapter 7: Energy

Kinetic energy (KE) is proportional to the square of the speed of the object; KE is therefore a number and **not **a vector. In order to understand how to use energy correctly, we will also need to discuss isolated systems, potential energy, and internal energy.

## Chapter 8: Momentum

It turns out that Σ **F**_{net} = m**a **is a special case of Newton's second law. Newton determined that a net force was something that caused a time rate of change of momentum, Δ**p/**Δt or d**p**/dt, where momentum is defined as **p** = m**v**. The two descriptions are the same if the mass of the object in question does not change. Therefore, if there is no net force acting on an object or a system of objects, the momentum does not change. This statement is called conservation of momentum. Conservation of momentum, along with conservation of energy, is used in analyzing collisions between objects.

## Chapter 9: Reference Frames

The subject of moving reference frames is of importance in the study of forces, energy and momentum (Chapters 4-8). Since both kinetic energy and momentum depend on the velocity, observers who disagree on the value of an object's velocity also will not agree on the value of the momentum or the kinetic energy. They are said to be viewing the motion from two different frames of reference. So who is measuring the **correct** value for the momentum and energy?

## Chapter 10: Rotations about a Fixed Axis

Many everyday objects undergo motion in a circle including: a spinning compact disk, the wheels (and other components) of a car, and a ceiling fan to name just a few.

While motion in a circle occurs in two dimensions, it turns out that this motion has a lot in common with motion on a line. We will analyze this motion using all of the techniques we have developed in one-dimensional and two-dimensional motion.

## Chapter 11: General Rotations

In the last chapter we studied rotational kinematics, rotational energy, and moment of inertia for objects rotating about a fixed axis. In this chapter we will begin by discussing the mathematical description of torque as a vector or cross product. We will also focus on general rotations such as when objects roll (rotate and translate).

## Chapter 12: Gravitation

Gravitational forces describe how massive objects are attracted to each other. As a consequence of its range, the gravitational force is an extremely important force for massive objects. But is the force responsible for the motion of the planets (a celestial gravitational force) the same force responsible for the motion of objects near the surface of the earth (terrestrial gravitational force)? Yes! In 1685 Newton proposed the idea of universal gravitation, a unification of celestial and terrestrial gravity.

## Chapter 13: Statics

Statics is primarily the study of bodies in static equilibrium. There are two conditions necessary for static equilibrium: the net force on a body equals zero and the net torque on a body equals zero. This is why we have waited until after discussing rotations to consider statics. Although any body with a constant velocity (of its center of mass) and a constant angular momentum is in equilibrium, the conditions of static equilibrium are most often applied to bodies that are at rest and not rotating. In many disciplines, especially mechanical engineering, understanding principles of statics is essential. After all, we hope that our buildings, bridges, cranes, etc., always maintain static equilibrium.