Science and Technology and Engineering: Physics (Review)

Laws of Thermodynamics
The laws of thermodynamics are generalized principles dealing with energy and heat.
The zeroth law of thermodynamics states that two objects in thermodynamic equilibrium with a third object are also in equilibrium with each other. Being in thermodynamic equilibrium basically means that different objects are at the same temperature.
The first law deals with conservation of energy. It states that neither mass nor energy can be destroyed; only converted from one form to The second law states that the entropy (the amount of energy in a system that is no longer available for work or the amount of disorder in a system) of an isolated system can only increase. The second law also states that heat is not transferred from a lower-temperature system to a higher-temperature one unless additional work is done.
The third law of thermodynamics states that as temperature approaches absolute zero, entropy approaches a constant minimum. It also states that a system cannot be cooled to absolute zero.

Heat and Temperature
Heat is energy transfer (other than direct work) from one body or system to another due to thermal contact. Everything tends to become less organized and less orderly over time (entropy). In all energy transfers, therefore, the overall result is that the energy is spread out uniformly. This transfer of heat energy from hotter to cooler objects is accomplished by conduction, radiation, or convection. Temperature is a measurement of an object's stored heat energy. More specifically, temperature is the average kinetic energy of an object's particles. When the temperature of an object increases and its atoms move faster, kinetic energy also increases. Temperature is not energy since it changes and is not conserved. Thermometers are used to measure temperature.

Mass, Weight, Volume, Density, and Specific Gravity
Mass - Mass is a measure of the amount of substance in an object.
Weight - Weight is a measure of the gravitational pull of Earth on an object.
Volume - Volume is a measure of the amount of space occupied. There are many formulas to determine volume. For example, the volume of a cube is the length of one side cubed () and the volume of a rectangular prism is length times width times height ().
The volume of an irregular shape can be determined by how much water it displaces.
Density - Density is a measure of the amount of mass per unit volume. The formula to find density is mass divided by volume
(D=m/V). It is expressed in terms of mass per cubic unit, such as grams per cubic centimeter ().
Specific gravity — This is a measure of the ratio of a substance's density compared to the density of water.

Thermal Contact
Thermal contact refers to energy transferred to a body by a means other than work. A system in thermal contact with another can exchange energy with it through the process of heat transfer. Thermal contact does not necessarily involve direct physical contact. Heat is energy that can be transferred from one body or system to another without work being done. Everything tends to become less organized and less useful over time
(entropy). In all energy transfers, therefore, the overall result is that the heat is spread out so that objects are in thermodynamic equilibrium and the heat can no longer be transferred without additional work.

Models for Flow of Electric Charge
Models that can be used to explain the flow of electric current, potential, and circuits include water, gravity, and roller coasters. For example, just as a mass can have a potential for energy based on its location, so can a charge within an electrical field. Just as a force is required to move an object uphill, a force is also required to move a charge from a low to high potential. Another example is water. Water does not flow when it is level. If it is lifted to a point and then placed on a downward path, it will flow. A roller coaster car requires work to be performed to transport it to a point where it has potential energy (the top of a hill). Once there, gravity provides the force for it to flow (move) downward. If either path is broken, the flow or movement stops or is not completed.

Atomic Structures

Magnetic Fields
The motions of subatomic structures (nuclei and electrons) produce a magnetic field. It is the direction of the spin and orbit that indicates the direction of the field. The strength of a magnetic field is known as the magnetic moment. As electrons spin and orbit a nucleus, they produce a magnetic field. Pairs of electrons that spin and orbit in opposite directions cancel each other out, creating a net magnetic field of zero.
Materials that have an unpaired electron are magnetic. Those with a weak attractive force are referred to as paramagnetic materials, while ferromagnetic materials have a strong attractive force. A diamagnetic material has electrons that are paired and, therefore, does not typically have a magnetic moment. There are, however, some diamagnetic materials that have a weak magnetic field.

Electric Charges
The attractive force between the electrons and the nucleus is called the electric force. A positive () charge or a negative () charge creates a field of sorts in the empty space around it, which is known as an electric field. The direction of a positive charge is away from it and the direction of a negative charge is towards it. An electron within the force of the field is pulled towards a positive charge because an electron has a negative charge. A particle with a positive charge is pushed away, or repelled, by another positive charge. Like charges repel each other and opposite charges attract. Lines of force show the paths of charges. The electric force between two objects is directly proportional to the product of the charge magnitudes and inversely proportional to the square of the distance between the two objects. Electric charge is measured with the unit Coulomb (C). It is the amount of charge moved in one second by a steady current of one ampere (1C = 1A × 1s).

Electric Current Movement Through Circuits
Electric current is the sustained flow of electrons that are part of an electric charge moving along a path in a circuit. This differs from a static electric charge, which is a constant non-moving charge rather than a continuous flow. The rate of flow of electric charge is expressed using the ampere (amp or A) and can be measured using an ammeter. A current of 1 ampere means that 1 coulomb of charge passes through a given area every second. Electric charges typically only move from areas of high electric potential to areas of low electric potential. To get charges to flow into a high potential area, you must connect it to an area of higher potential by introducing a battery or other voltage source.

Simple Circuits
Movement of electric charge along a path between areas of high electric potential and low electric potential, with a resistor or load device between them, is the definition of a simple circuit. It is a closed conducting path between the high and low potential points, such as the positive and negative terminals on a battery. One example of a circuit is the flow from one terminal of a car battery to the other. The electrolyte solution of water and sulfuric acid provides work in chemical form to start the flow. A frequently used classroom example of circuits involves using a D cell (1.5 V) battery, a small light bulb, and a piece of copper wire to create a circuit to light the bulb.

Magnets
A magnet is a piece of metal, such as iron, steel, or magnetite (lodestone) that can affect another substance within its field of force that has like characteristics.
Magnets can either attract or repel other substances. Magnets have two poles: north and south. Like poles repel and opposite poles (pairs of north and south) attract. The magnetic field is a set of invisible lines representing the paths of attraction and repulsion. Magnetism can occur naturally, or ferromagnetic materials can be magnetized. Certain matter that is magnetized can retain its magnetic properties indefinitely and become a permanent magnet. Other matter can lose its magnetic properties. For example, an iron nail can be temporarily magnetized by stroking it repeatedly in the same direction using one pole of another magnet. Once magnetized, it can attract or repel other magnetically inclined materials, such as paper clips. Dropping the nail repeatedly will cause it to lose its charge.

Magnetic Fields, Current, and Magnetic Domains
A magnetic field can be formed not only by a magnetic material, but also by electric current flowing through a wire. When a coiled wire is attached to the two ends of a battery, for example, an electromagnet can be formed by inserting a ferromagnetic material such as an iron bar within the coil. When electric current flows through the wire, the bar becomes a magnet. If there is no current, the magnetism is lost. A magnetic domain occurs when the magnetic fields of atoms are grouped and aligned. These groups form what can be thought of as miniature magnets within a material. This is what happens when an object like an iron nail is temporarily magnetized. Prior to magnetization, the organization of atoms and their various polarities are somewhat random with respect to where the north and south poles are pointing.
After magnetization, a significant percentage of the poles are lined up in one direction, which is what causes the magnetic force exerted by the material.

Motion and Displacement
Motion is a change in the location of an object and is the result of an unbalanced net force acting on the object. Understanding motion requires an understanding of three basic quantities: displacement, velocity, and acceleration.
When something moves from one place to another, it has undergone displacement. Displacement along a straight line is a very simple example of a vector quantity. If an object travels from position

to
, it has undergone a displacement of 10 cm. If it traverses the same path in the opposite direction, its displacement is -10 cm. A vector that spans the object's displacement in the direction of travel is known as a displacement vector.

Gravitational Force
Gravitational force is a universal force that causes every object to exert a force on every other object. The gravitational force between two objects can be described by the formula,
, where

and

are the masses of two objects, r is the distance between them, and G is the gravitational constant,
. In order for this force to have a noticeable effect, one or both of the objects must be extremely large, so the equation is generally only used in problems involving planetary bodies. For problems involving objects on the earth being affected by earth's gravitational pull, the force of gravity is simply calculated as
, where g is

toward the ground.

Newton's First Two Laws of Motion

Newton's First Law
An object at rest or in motion will remain at rest or in motion unless acted upon by an external force.
This phenomenon is commonly referred to as inertia, the tendency of a body to remain in its present state of motion. In order for the body's state of motion to change, it must be acted on by an unbalanced force.

Newton's Second Law

An object's acceleration is directly proportional to the net force acting on the object and inversely proportional to the object's mass.
This law is generally written in equation form   is the net force acting on a body,  'm' is the mass of the body, and 'a' is its acceleration. Note that since the mass is always a positive quantity, the acceleration is always in the same direction as the force.

Simple Machines

Simple machines include the inclined plane, lever, wheel and axle, and pulley. These simple machines have no internal source of energy. More complex or compound machines can be formed from them. Simple machines provide a force known as a mechanical advantage and make it easier to accomplish a task. The inclined plane enables a force less than the object. The wheel and axle allows for movement with less resistance. Single or double pulleys allow for easier direction of force. The wedge and screw are forms of the inclined plane. A wedge turns a smaller force working over a greater distance into a larger force. The screw is similar to an incline that is wrapped around a shaft.

Friction
Friction is a force that arises as a resistance to motion where two surfaces are in contact.
The maximum magnitude of the frictional force (f)can be calculated as
, where

is the contact force between the two objects and µ is a coefficient of friction based on the surfaces' material composition. Two types of friction are static and kinetic. To illustrate these concepts, imagine a book resting on a table. The force of its weight (W) is equal and opposite to the force of the table on the book, or the normal force (N). If we exert a small force (F) on the book, attempting to push it to one side, a frictional force (f) would arise, equal and opposite to our force. At this point, it is a static frictional force because the book is not moving. If we increase our force on the book, we will eventually cause it to move. At this point, the frictional force opposing us will be a kinetic frictional force. Generally, the kinetic frictional force is lower than static frictional force (because the frictional coefficient for static friction is larger), which means that the amount of force needed to maintain the movement of the book will be less than what was needed to start it moving.

Sound
Sound is a pressure disturbance that moves through a medium in the form of mechanical waves, which transfer energy from one particle to the next. Sound requires a medium to travel through, such as air, water, or other matter since it is the vibrations that transfer energy to adjacent particles, not the actual movement of particles over a great distance. Sound is transferred through the movement of atomic particles, which can be atoms or molecules. Waves of sound energy move outward in all directions from the source. Sound waves consist of compressions (particles are forced together) and rarefactions (particles move farther apart and their density decreases). A wavelength consists of one compression and one rarefaction. Different sounds have different wavelengths. Sound is a form of kinetic energy.

Pitch, Loudness, Sound Intensity, Timbre, and Oscillation
Pitch - Pitch is the quality of sound determined by frequency. For example, a musical note can be tuned to a specific frequency. A, for instance, has a frequency of 440 Hz, which is a higher frequency than middle C. Humans can detect frequencies between about 20 Hz to 20,000 Hz.
Loudness - Loudness is a human's perception of sound intensity.
Sound intensity - Sound intensity is measured as the sound power per unit area and can be expressed in decibels.
Timbre - This is a human's perception of the type or quality of sound.
Oscillation - This is a measurement, usually of time, against a basic value, equilibrium, or rest point.

Doppler Effect
The Doppler effect refers to the effect the relative motion of the source of the wave and the location of the observer has on waves.
The Doppler effect is easily observable in sound waves. What a person hears when a train approaches or a car honking its horn passes by are examples of the Doppler effect. The pitch of the sound is different not because the emitted frequency has changed, but because the received frequency has changed.
The frequency is higher (as is the pitch) as the train approaches, the same as emitted just as it passes, and lower as the train moves away. This is because the wavelength changes. The Doppler effect can occur when an observer is stationary, and can also occur when two trains approach and pass each other. Electromagnetic waves are also affected in this manner. The motion of the medium can also affect the wave. For waves that do not travel in a medium, such as light waves, it is the difference in velocity that determines the outcome.

Waves
Waves have energy and can transfer energy when they interact with matter. Although waves transfer energy, they do not transport matter. They are a disturbance of matter that transfers energy from one particle to an adjacent particle. There are many types of waves, including sound, seismic, water, light, micro, and radio waves. The two basic categories of waves are mechanical and electromagnetic. Mechanical waves are those that transmit energy through matter. Electromagnetic waves can transmit energy through a vacuum. A transverse wave provides a good illustration of the features of a wave, which include crests, troughs, amplitude, and wavelength.

Electromagnetic Spectrum
The electromagnetic spectrum is defined by frequency (f) and wavelength (λ). Frequency is typically measured in hertz and wavelength is usually measured in meters. Because light travels at a fairly constant speed, frequency is inversely proportional to wavelength, a relationship expressed by the formula , where c is the speed of light (about 300 million meters per second). Frequency multiplied by wavelength equals the speed of the wave; for electromagnetic waves, this is the speed of light, with some variance for the medium in which it is traveling.
Electromagnetic waves include (from largest to smallest wavelength) radio waves, microwaves, infrared radiation (radiant heat), visible light, ultraviolet radiation, x-rays, and gamma rays. The energy of electromagnetic waves is carried in packets that have a magnitude inversely proportional to the wavelength. Radio waves have a range of wavelengths, from about   to  
meters, while their frequencies range from about  to  Hz.

Visible Light
Light is the portion of the electromagnetic spectrum that is visible because of its ability to stimulate the retina. It is absorbed and emitted by electrons, atoms, and molecules that move from one energy level to another. Visible light interacts with matter through molecular electron excitation (which occurs in the human retina) and through plasma oscillations (which occur in metals). Visible light is between ultraviolet and infrared light on the spectrum. The wavelengths of visible light cover a range from 380 nm (violet) to 760 nm (red). Different wavelengths correspond to different colors.

Reflection and Refraction
Reflection is the rebound of a light wave from a surface back toward the medium from where it came. A light wave that hits a reflecting surface at a 90-degree angle retraces its original path back to its source. Striking the surface at any other angle results in reflection of the wave at an angle in the opposite direction.
Reflectance is the amount of light a material reflects; metals have high reflectance. The smoother a surface, the higher its reflectance. Refraction is the change in the direction of a light wave when it passes through a transparent medium with a different optical density from the one in which the wave had been traveling. This results in a change in the wave's velocity. The ratio of the sine of the angle of the incoming ray to the sine of the angle of refraction is equal to the ratio of the speed of light in the original medium to the speed of light in the refracting medium.