Chapter Outline

Physics

Physics is the study of energy in all its forms:

• mechanical energy
• heat
• electricity
• magnetism
• light
• nuclear power
• solar energy
• geothermal energy

Laws of Motion

One of the great advances in science occurred during the 1600s when Isaac Newton discovered natural laws that govern the motion of objects:

• The Law of Inertia: If no force is applied, an object at rest will remain at rest, and an object in motion will move in a straight line at constant speed.
• The Law of Acceleration, Part I: An object's speed increases in proportion to the amount of force applied.
• The Law of Acceleration, Part 2: For the same amount of applied force, a lighter object accelerates—changes its speed—at a greater rate than a heavier object.
• The Law of Interaction: For every action, there is an equal and opposite reaction.

Newton used his laws of motion to discover the Law of Universal Gravitation:

• Part 1: Gravitational force is an attractive force, a force that pulls two objects toward one another.
• Part 2: Gravitational force is greater for heavy objects (objects with more mass) than for light objects.
• Part 3: The force of gravity decreases as the distance between objects increases.

Force, Work, and Machines

Scientists define work as the product of the units of force times the units of distance. For work to occur, there must be force applied to an object and the object must move:

Machines are devices that are designed to make work easier.

• A lever is a simple machine that consists of a bar that moves around a pivot point called a fulcrum. A lever changes a small prying force into a much larger one.
• A wheel and axle is a simple machine that changes a small turning force into a much larger one.

Law of Conservation of Energy: During interactions, energy may change from one form to another, but no energy is lost. The total amount of energy present remains constant.

• Kinetic energy—energy of motion
• Potential energy—stored energy

Friction is a force that either slows a moving object or prevents a nonmoving object from being moved:

• Sliding friction—friction felt when one object rubs against another
• Rolling friction—friction felt when an object is placed on wheels and moved
• Fluid friction—friction felt when an object moves through a fluid, such as water or air
• Static friction—friction felt when a force is applied to an object that doesn't move

Forms of Energy

Among the most familiar forms of energy are the following:

• Heat is energy of molecular motion. As heat is added to an object, the atoms or molecules of that object speed up.
• Both water and sound are examples of energy that is carried as waves through material substances. Sound waves travel through air, and they can also travel through any liquid or solid substance. Sound will not travel through a vacuum and cannot travel in outer space.
• Light waves are the most common example of electromagnetic energy. Unlike other forms of energy, light can travel through the vacuum of space.
• Electricity is energy carried by the flow of electrons. Electric current can be direct current (flows in one direction only) or alternating current (flows back and forth).
• Magnetic energy is energy carried in a magnetic field. Magnetism occurs naturally in some substances, and it can also be created by an electric current. Electromagnets are commonly used in consumer products.
• Nuclear energy occurs naturally as radioactive elements decay.

Our Energy Future

The following four sources of energy have the advantage of being nonpolluting. With more research and technical advances, any of these sources may become more important in our energy future.

• Hydroelectric power comes from changing the energy of flowing (or stored) river water into electricity.
• Solar energy is energy from sunlight. Solar energy is unlimited and is the cleanest source of energy possible.
• Geothermal energy is energy from Earth's hot interior. Controlled geothermal energy is available only in very limited supply from natural hot springs.
• Wind energy has been used for centuries to power windmills and provide mechanical energy to individual farms in Europe.