Laws of Motion

A force is anything that can change the state of motion of an object, like a push or a pull. You use force when you push a letter on the computer keyboard or when you kick a ball. Forces are everywhere. Gravity acts as a constant force on your body, keeping you secure on planet Earth so you don't float away. To describe a force we use the direction and strength. For example when you kick a ball you are exerting force in a specific direction. That is the direction the ball will travel. Also, the harder you kick the ball the stronger the force you place on it and the farther it will go. A scientist named Isaac Newton came up with three Laws of Motion to describe how things move scientifically. He also described how gravity works, which is an important force that affects everything.

First Law of Motion The first law says that any object in motion will continue to move in the same direction and speed unless forces act on it. That means if you kick a ball it will fly forever unless some sort of forces act on it! As strange as this may sound, it's true. When you kick a ball, forces start to act on it immediately. These include resistance or friction from the air and gravity. Gravity pulls the ball down to the ground and the air resistance slows it down.

Second Law of Motion The second law states that the greater the mass of an object, the more force it will take to accelerate the object. There is even an equation that says Force = mass x acceleration or F=ma. This also means that the harder you kick a ball the farther it will go. This seams kind of obvious to us, but having an equation to figure out the math and science is very helpful to scientists.

Third Law of Motion The third law states that for every action, there is an equal and opposite reaction. This means that there are always two forces that are the same. In the example where you kicked the ball there is the force of your foot on the ball, but there is also the same amount of force that the ball puts on your foot. This force is in the exact opposite direction.

Fun facts about Forces and Motion It is said that Isaac Newton got the idea for gravity when an apple fell off a tree and hit him on

the head. Gases and liquids push out in equal forces in all directions. This is called Pascal's Law because

it was discovered by the scientist Blaise Pascal. When you go upside down in a roller coaster loop-the-loop, a special kind of force called

"centripetal force" keeps you in your seat and from falling out.

Energy

What is Energy?The simplest definition of energy is "the ability to do work". Energy is how things change and move. It's everywhere around us and takes all sorts of forms. It takes energy to cook food, to drive to school, and to jump in the air.

Different forms of Energy Energy can take a number of different forms. Here are some examples: Chemical - Chemical energy comes from atoms and molecules and how they interact. Electrical - Electrical energy is generated by the movement of electrons. Gravitational - Large objects such as the Earth and the Sun create gravity and gravitational energy. Heat - Heat energy is also called thermal energy. It comes from molecules of different temperatures interacting. Light - Light is called radiant energy. The Earth gets a lot of its energy from the light of the Sun. Motion - Anything that is moving has energy. This is also called kinetic energy. Nuclear - Huge amounts of nuclear energy can be generated by splitting atoms. Potential - Potential energy is energy that is stored. One example of this is a spring that is pressed all the way down. Another example is a book sitting high on a shelf.

Units of Measure for Energy In physics, the standard unit of measure for energy is the joule which is abbreviated as J. There are other units of measure for energy that are used throughout the world including kilowatt-hours, calories, newton-meters, therms, and foot-pounds.

Law of Conservation of Energy This law states that energy is never created or destroyed, it is only changed from one state to another. One example is the chemical energy in food that we turn into kinetic energy when we move.

Renewable and Nonrenewable As humans we use a lot of energy to drive our cars, heat and cool our houses, watch TV, and more. This energy comes from a variety of places and in a number of forms. Conservationists classify the energy we use into two types: renewable and nonrenewable. Nonrenewable energy uses up resources that we cannot recreate. Some examples of this are gas to run our car and coal burned in power plants. Once they are used, they are gone forever. A renewable energy source is one that can be replenished. Examples of this include hydropower from turbines in a dam, wind power from windmills, and solar power from the sun. The more renewable power we use the better for our planet and for future generations as they won't run out of resources someday.

Fun Facts about Energy In 2008 about 7% of the energy used in the United States was from renewable sources. A modern windmill or turbine can generate enough electricity to power around 300 homes. People have used waterpower to grind grain for over 2,000 years. Geothermal power uses energy from geysers, hot springs, and volcanoes. The entire world could be powered for a year from the energy from the sun that falls on the Earth's surface in one hour. We just need to figure out how to harness it!

Heat

Heat is the transfer of energy from a one object to another due to a difference in temperature. Heat can be measured in joules, BTUs (British thermal unit), or calories. Heat and temperature are closely related, but they are not the same thing. The temperature of an object is determined by how fast its molecules are moving. The faster the molecules are moving the higher the temperature. We say objects that have a high temperature are hot and objects with a low temperature are cold.

Transferring of Heat When two items are combined or touching each other, their molecules will transfer energy called heat. They will try to come to a point where they both have the same temperature. This is called equilibrium. Heat will flow from the hotter object to the colder. The molecules in the hotter object will slow down and the molecules in the colder object will speed up. Eventually they will get to the point where they have the same temperature. This happens all the time around you. For example, when you take an ice cube and put it into a warm soda. The ice cube will become warmer and melt, while the soda will cool down.

Hot Objects Expand When something gets hotter it will expand, or get bigger. At the same time, when something gets colder it will shrink. This property is used to make mercury thermometers. The line in the thermometer is actually liquid mercury. As the liquid gets hotter, it will expand and rise in the thermometer to show a higher temperature. It's the expansion and contraction due to temperature that allows the thermometer to work.

Heat Conduction When heat transfers from one object to another, this is called conduction. Some materials conduct heat better than others. Metal, for example, is a good conductor of heat. We use metal in pots and pans to cook because it will move the heat from the flame to our food quickly. Cloth, like a blanket, isn't a good conductor of heat. Because it's not a good conductor, a blanket works well to keep us warm at night as it won't conduct the heat from our bodies out to the cold air.

Matter Changing State Heat has an impact on the state of matter. Matter can change state based on heat or temperature. There are three states that matter can take depending on its temperature: solid, liquid, and gas. For example, if water is cold and its molecules are moving very slow, it will be a solid (ice). If it warms up some, the ice will melt and water becomes a liquid. If you add a lot of heat to water, the molecules will move very fast and it will become a gas (steam).

Waves

What is a wave? When we think of the word "wave" we usually picture someone moving their hand back and forth to say hello or maybe we think of a tall curling wall of water moving in from the ocean to crash on the beach. In physics, a wave is a traveling disturbance that travels through space and matter transferring energy from one place to another. When studying waves it's important to remember that they transfer energy, not matter.

Waves in Everyday Life There are lots of waves all around us in everyday life. Sound is a type of wave that moves through matter and then vibrates our eardrums so we can hear. Light is a special kind of wave that is made up of photons that helps us to see. You can drop a rock into a pond and see waves form in the water. We even use waves (microwaves) to cook our food really fast.

Types of Waves Waves can be divided into various categories depending on their characteristics. Below we describe some of the different terms that scientists use to describe waves.

Mechanical Waves and Electromagnetic Waves All waves can be categorized as either mechanical or electromagnetic.Mechanical waves are waves that require a medium. This means that they have to have some sort of matter to travel through. These waves travel when molecules in the medium collide with each other passing on energy. One example of a mechanical wave is sound. Sound can travel through air, water, or solids, but it can't travel through a vacuum. It needs the medium to help it travel. Other examples include water waves, seismic waves, and waves traveling through a spring. Electromagnetic waves are waves that can travel through a vacuum (empty space). They don't need a medium or matter. They travel through electrical and magnetic fields that are generated by charged particles. Examples of electromagnetic waves include light, microwaves, radio waves, and X-rays.

Transverse Waves and Longitudinal WavesAnother way to describe a wave is by the direction that its disturbance is traveling. Transverse waves are waves where the disturbance moves perpendicular to the direction of the wave. You can think of the wave moving left to right, while the disturbance moves up and down. One example of a transverse wave is a water wave where the water moves up and down as the wave passes through the ocean. Other examples include an oscillating string and a wave of fans in a stadium (the people move up and down while the wave moves around the stadium). Longitudinal waves are waves where the disturbance moves in the same direction as the wave. One example of this is a wave moving through a stretched out slinky or spring. If you compress one portion of the slinky and let go, the wave will move left to right. At the same time, the disturbance (which is the coils of the springs moving), will also move left to right. Another classic example of a longitudinal wave is sound. As sound waves propagate through a medium, the molecules collide with each other in the same direction as the sound is moving. In the above picture the top wave is transverse and the bottom wave is longitudinal.

Interesting Facts about Waves Waves in the ocean are mostly generated by the wind moving across the ocean surface. The "medium" is the substance or material that carries a mechanical wave. One of the most important things to remember about waves is that they transport energy, not

matter. This makes them different from other phenomenon in physics.

Many waves cannot be seen such as microwaves and radio waves. The tallest ocean wave ever recorded was 1,720 feet tall and occurred in Lituya Bay in Alaska.

Temperature

What is temperature? Temperature can be a difficult property to define. In our everyday lives we use the word temperature to describe the hotness or coldness of an object. In physics, the temperature is the average kinetic energy of the moving particles in a substance.

How is temperature measured? Temperature is measured using a thermometer. There are different scales and standards for measuring temperature including Celsius, Fahrenheit, and Kelvin. These are discussed in more detail below.

How does a thermometer work? Thermometers take advantage of a scientific property called thermal expansion. Most substances will expand and take up more volume as they get hotter. Liquid thermometers have some sort of substance (this used to be mercury, but today is generally alcohol) that is enclosed in a small glass tube. As the temperature rises, the liquid expands and fills up more of the tube. When the temperature drops, the liquid contracts and takes up less of the tube. The temperature can then be read by the lines calibrated on the side of the tube.

Temperature Scales There are three main temperature scales that are used today: Celsius, Fahrenheit, and Kelvin. Celsius - The most common temperature scale in the world is Celsius. Celsius uses the unit "degrees" and is abbreviated as °C. The scale sets the freezing point of water at 0 °C and the boiling point of water at 100 °C. Fahrenheit - The temperature scale most common in the United States is the Fahrenheit scale. Fahrenheit sets the freezing point of water at 32 °F and the boiling point at 212 °F. Kelvin - The standard unit of temperature that is most used by scientists is Kelvin. Kelvin doesn't use the ° symbol like the other two scales. When writing a temperature in Kelvin you just use the letter K. Kelvin uses absolute zero as the 0 point of its scale. It has the same increments as Celsius in that there are 100 increments between the freezing and boiling points of water.

Temperature and the State of Matter Temperature has an effect on the state of matter. Each substance of matter will go through different phases as the temperature increases including solid, liquid, and gas. One example of this is water which changes from ice (solid) to water (liquid) to vapor (gas) as the temperature increases.

Interesting Facts about Temperature Temperature is independent of the size or quantity of an object. This is called an intensive

property. The Fahrenheit scale is named after Dutch physicist Daniel Fahrenheit. Temperature is a different quantity from the total amount of thermal energy in a substance,

which is dependent on the size of the object. Celsius was named after the Swedish astronomer Anders Celsius. Celsius was originally known

as "centigrade." As substances approach absolute zero they can achieve some interesting properties such as

superfluidity and superconductivity.

Work

What is work? We often use the word "work" in our everyday lives. For example, we would say that getting good grades in school takes a lot of hard "work". In physics, the term "work" has a specific meaning. Work, in physics, occurs when a force acts on an object to move it some distance from the start point (also called displacement). Work is calculated as the force times the distance. The following equation is used to describe work: Work = Force * distance or W = Fd

How to Measure Work The standard unit for work is the joule (J). The joule is the same as a newton-meter where the newton is the force and the meter is the distance.

Force and Displacement The distance (or displacement) in work is the distance from the start point to the end point. The amount of traveling in between doesn't matter. For example, if you lift a weight off the ground and then place it back on the ground the distance (or displacement) is zero.

Don't be Tricked Measuring work can sometimes be tricky. In order for the equation W = Fd to work, the force used in the equation must be the force used to cause the displacement or distance. Also, remember for work to have occurred, the object must be displaced by the force. Otherwise, the distance, or "d", in the formula is 0 and the work will be 0. Here are some examples: If someone is pushing on a wall with all their might, but the wall doesn't move, no work has occurred. This is because the distance is zero. If someone is using force to hold a rock over their head while walking eastward across a field, no work has occurred. This is because the force is not in the same direction (the force is up) as the distance moved by the rock (eastward). If you do a full push-up, lifting yourself up and then back down, the total work is zero. This is because the total distance from the starting point to the ending point is zero. If you drop your pencil, then work has occurred. This is because the displacement of the pencil from your hand to the ground is greater than zero and is in the same direction as the force acting on the pencil, which is gravity.

Example problem: A baseball player throws a ball with a force of 10 N. The ball travels 20 meters. What is the total work? W = F * distance W = 10 N* 20 meters W = 200 joules

More Complicated Problems When the angle between the force and displacement is not 0 degrees or 90 degrees, a more complex formula for work is used. This formula includes the angle theta (Θ) which is the angle between the force and displacement. W = F * d * cos Θ In the case where the force and the displacement are in the exact same direction theta = 0 and the cos Θ = 1. In the case where the force has no impact on the displacement and theta = 90 degrees, then cos Θ = 0 and, therefore, the work = 0.

Interesting Facts about Work Work is a scalar quantity, not a vector quantity. This means that, unlike force and velocity, it

has no direction, only a magnitude. Another unit of work is the foot-pound. One foot-pound is equal to 1.35581795 joules. The joule is also used as the standard unit of measure for energy.

Negative work is when force acting on an object hinders the object's displacement.

Electricity

Important things to know about electricity?

Conductors and insulators - Conductors are materials that allow electricity to flow easily. Most types of metal are good conductors, which is why we use metal for electrical wire. Copper is a good conductor and isn't too expensive, so it's used a lot for the wiring in homes today. Insulators are the opposite of conductors. An insulator is a material that doesn't carry electricity. Insulators are important because they can protect us from electricity. Materials like rubber, plastic, and paper are good insulators.

Voltage - Voltage is the name for the electric force that causes electrons to flow. It's the measure of potential difference between two points in the circuit. Voltage may come from a battery or a power plant.

Current - Current is the measure of the flow of electrons in a circuit. Current is measured in Amps or Amperes.

Power (Watts) - The power or energy used by a circuit is measured in Watts. You can calculate the number of Watts by multiplying the Voltage times the Current. When your parents get their electrical bill it's generally in kilowatt hours. This is the measurement of power over time or how much power was used that month.

Resistance - Resistance measures how well a material or object conducts electricity. Low resistance means the object conducts electricity well, high resistance means the object does not conduct electricity well.

Battery A battery can act as a source of electricity in circuits. It stores up electric power and then provides a voltage across a circuit causing power to flow through the circuit. Batteries use chemicals that react to make electricity. They have a positive connection called the anode and a negative connection called the cathode. When a circuit with a load is placed across the anode and cathode, the chemicals react causing electricity to flow through the circuit. The chemicals in batteries only last so long, so batteries have a limited amount of electricity and eventually will run out.

Alternate and Direct CurrentThere are two main types of current used in electrical systems today: alternate current (AC) and direct current (DC). Batteries, and most electronics, use direct current. This is where current always flows in one direction. Power stations that generate power for our homes generate current that constantly changes direction (60 times each second). Therefore the power that we get from our wall outlets is AC current.

Static Electricity Sometimes electric charges can build up on the surface of objects. This is called static electricity. When you put on your clothes and they sometimes "stick" to your body or have an attraction to you, this is static electricity. When your hair sometimes goes straight up for no reason, this can be static electricity. If you rub a balloon against your clothes, you can build up a static electricity charge on the balloon that will cause it to stick to a wall. Static electricity can sometimes damage electronic components. There are anti-static bags and other ways to protect components from getting damaged.

Electric Current

Current is the flow of an electric charge. It is an important quantity in electronic circuits. Current flows through a circuit when a voltage is placed across two points of a conductor.

Flow of Electrons In an electronic circuit, the current is the flow of electrons. However, generally current is shown in the direction of the positive charges. This is actually in the opposite direction of the movement of the electrons in the circuit.

How is current measured? The standard unit of measurement for current is the ampere. It is sometimes abbreviated as A or amps. The symbol used for current is the letter "i." Current is measured as the flow of electric charge over time past a given point in an electric circuit. One ampere is equal to 1 coulomb over 1 second. A coulomb is a standard unit of electric charge.

Calculating Current Current can be calculated using Ohm's Law. It can also be used to figure out the resistance of a circuit if the voltage is also known or the voltage of a circuit if the resistance is known. I = V/R where I = current, V = voltage, and R = resistance Current is also used to calculate power using the following equation: P = I * V where P = power, I = current, and V = voltage.

AC versus DC There are two main types of current used in most electronic circuits today. They are alternating current (AC) and direct current (DC). Direct Current (DC) - Direct current is the constant flow of electric charge in one direction. Batteries generate direct current to power handheld items. Most electronics use direct current for internal power often converting alternating current (AC) to direct current (DC) using a transformer. Alternating Current (AC) - Alternating current is current where the flow of electric charge is constantly changing directions. Alternating current is mostly used today to transmit power on power lines. In the United States the frequency at which the current alternates is 60 Hertz. Some other countries use 50 Hertz as the standard frequency.

Electromagnetism Current also plays an important role in electromagnetism. Ampere's law describes how a magnetic field is generated by an electric current. This technology is used in electric motors.

Interesting Facts about Current The direction of the current flow is often shown with an arrow. In most electronic circuits the

current is shown as flowing towards ground. The current in a circuit is measured using a tool called an amperemeter. The flowing of electric current through a wire can sometimes be thought of like the flowing of

water through a pipe. The electrical conductivity of a material is the measurement of the ability of the material to

allow for the flow of electrical current.

Magnetism

Magnetism is an invisible force or field caused by the unique properties of certain materials. In most objects, electrons spin in different, random directions. This causes them to cancel each other out over time. However, magnets are different. In magnets the molecules are uniquely arranged so that their electrons spin in the same direction. This arrangement of atoms creates two poles in a magnet, a North-seeking pole and a South-seeking pole.

Magnets Have Magnetic Fields The magnetic force in a magnet flows from the North pole to the South pole. This creates a magnetic field around a magnet. Have you ever held two magnets close to each other? They don't act like most objects. If you try to push the South poles together, they repel each other. Two North poles also repel each other. Turn one magnet around, and the North (N) and the South (S) poles are attracted to each other. Just like protons and electrons - opposites attract.

Where do we get magnets? Only a few materials have the right type of structures to allow the electrons to line up just right to create a magnet. The main material we use in magnets today is iron. Steel has a lot of iron in it, so steel can be used as well.

The Earth is a giant magnet At the center of the Earth spins the Earth's core. The core is made up of mostly iron. The outer portion of the core is liquid iron that spins and makes the earth into a giant magnet. This is where we get the names for the north and south poles. These poles are actually the positive and negative poles of the Earth's giant magnet. This is very useful to us here on Earth as it lets us use magnets in compasses to find our way and make sure we are heading in the right direction. It's also useful to animals such as birds and whales who use the Earth's magnetic field to find the right direction when migrating. Perhaps the most important feature of the Earth's magnetic field is that it protects us from the Sun's solar wind and radiation.

The Electric Magnet and Motor Magnets can also be created by using electricity. By wrapping a wire around an iron bar and

running current through the wire, very strong magnets can be created. This is called electromagnetism. The magnetic field created by electromagnets can be used in a variety of applications. One of the most important is the electric motor.

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Electromagnetism and Electric Motors

Electromagnetism The word "electromagnetism" in physics is used to describe one of the fundamental forces of nature. This force is between subatomic particles such as protons and electrons. It helps to hold matter together. Electromagnetism is also used to describe how a magnetic field is created by the flowing of electric current. We will be discussing this type of electromagnetism on this page.

Electromagnet When an electronic current flows through a wire, it generates a magnetic field. This is an important concept in electricity. The magnetic field can be increased by coiling the wire. This allows more current to flow through a smaller distance and increases the magnetic field.

Right-Hand Rule When current is flowing through a wire, the magnetic field rotates around the wire. The direction of the current determines the direction of the magnetic field. You can figure out the direction of the magnetic field using the "right-hand rule". To determine the direction of the magnetic field, look at the picture above. Take your right hand and point your thumb in the direction of the current (I). Now wrap your fingers around the wire. Your fingers will point in the direction of the rotation of the magnetic field (B).

Motors One of the important applications of electromagnetism is the electric motor. An electric motor converts electrical energy into physical movement. Electric motors generate magnetic fields with electric current through a coil. The magnetic field then causes a force with a magnet that causes movement or spinning that runs the motor. Electric motors are used in all sorts of applications. There are even several electric motors inside your computer including one to turn the fan, one to open and shut the CDROM drive, and one to operate the hard drive.

Electromagnetic Induction Another important application of electromagnetism is induction. Induction is when movement is used to create electricity (the opposite of using electricity to create movement). As a wire is moved through a magnetic field, current will begin to flow through it.

Generators Electric generators convert mechanical energy into electrical energy using induction. As a coil of wire is spun between two opposite magnets, an electric current is generated that can be used to power electronic devices. Generators can get their power from a wide variety of sources. Two popular electric generators of renewable energy include hydropower and wind power.

Fun Facts about Electromagnetism and Electric Motors Some electric generators can be driven by human power such as a hand crank or a bicycle to

generate electricity. Danish physicist Hans Orsted was the first to discover that a magnetic field was produced by

the flow of electric current. American physicist Joseph Henry discovered electromagnetic inductance and built the first

electromagnetic motor. Loudspeakers use electromagnets to vibrate the cone and produce sound.

Using electromagnetism, powerful magnets can be turned on and off using electricity, unlike permanent magnets.

Electromagnetic Waves

Electromagnetic waves are a form of energy waves that have both an electric and magnetic field. Electromagnetic waves are different from mechanical waves in that they can transmit energy and travel through a vacuum. Electromagnetic waves are classified according to their frequency. The different types of waves have different uses and functions in our everyday lives. The most important of these is visible light, which enables us to see.

Radio Waves Radio waves have the longest wavelengths of all the electromagnetic waves. They range from around a foot long to several miles long. Radio waves are often used to transmit data and have been used for all sorts of applications including radio, satellites, radar, and computer networks.

Microwaves Microwaves are shorter than radio waves with wavelengths measured in centimeters. We use microwaves to cook food, transmit information, and in radar that helps to predict the weather. Microwaves are useful in communication because they can penetrate clouds, smoke, and light rain. The universe is filled with cosmic microwave background radiation that scientists believe are clues to the origin of the universe they call the Big Bang.

Infrared Between microwaves and visible light are infrared waves. Infrared waves are sometimes classified as "near" infrared and "far" infrared. Near infrared waves are the waves that are closer to visible light in wavelength. These are the infrared waves that are used in your TV remote to change channels. Far infrared waves are further away from visible light in wavelength. Far infrared waves are thermal and give off heat. Anything that gives off heat radiates infrared waves. This includes the human body!

Visible light The visible light spectrum covers the wavelengths that can be seen by the human eye. This is the range of wavelengths from 390 to 700 nm which corresponds to the frequencies 430-790 THz. You can go here to learn more about the visible spectrum.

Ultraviolet Ultraviolet waves have the next shortest wavelength after visible light. It is ultraviolet rays from the Sun that cause sunburns. We are protected from the Sun's ultraviolet rays by the ozone layer. Some insects, such as bumblebees, can see ultraviolet light. Ultraviolet light is used by powerful telescopes like the Hubble Space Telescope to see far away stars.

X-rays X-rays have even shorter wavelengths than ultraviolet rays. At this point in the electromagnetic spectrum, scientists begin to think of these rays more as particles than waves. X-rays were discovered by German scientist Wilhelm Roentgen. They can penetrate soft tissue like skin and muscle and are used to take X-ray pictures of bones in medicine.

Gamma rays As the wavelengths of electromagnetic waves get shorter, their energy increases. Gamma rays are the shortest waves in the spectrum and, as a result, have the most energy. Gamma rays are sometimes used

in treating cancer and in taking detailed images for diagnostic medicine. Gamma rays are produced in high energy nuclear explosions and supernovas.

Optics

What is light made of? This is not an easy question. Light has no mass and is not really considered matter. So does it even exist? Of course it does! We couldn't live without light. Today scientists say light is a form of energy made of photons. Light is unique in that it behaves like both a particle and a wave.

Why does light go through some things and not others? Depending on the type of matter it comes into contact with, light will behave differently. Sometimes light will pass directly through the matter, like with air or water. This type of matter is called transparent. Other objects completely reflect light, like an animal or a book. These objects are called opaque. A third type of object does some of both and tends to scatter the light. These objects are called translucent objects.

Light helps us to survive Without sunlight our world would be a dead dark place. Sunlight does more than just help us see (which is pretty great, too). Sunlight keeps the Earth warm, so it's not just a frozen ball in outer space. It also is a major component in photosynthesis which is how most of the plant life on Earth grows and gets nutrients. Sunlight is a source of energy as well as a source of vitamin D for humans.

The speed of light Light moves at the fastest known speed in the universe. Nothing moves faster than (or even close to) the speed of light. In a vacuum, where there is nothing to slow it down, light travels 186,282 miles per second! Wow, that's fast! When light travels through matter, like air or water, it slows down some, but it's still pretty fast. To give you and idea as to how fast light is, we'll give you some examples. The sun is almost 93 million miles from the Earth. It takes around 8 minutes for light to get from the sun to the Earth. It takes around 1.3 seconds for light to go from the moon to the Earth.

Refraction Normally, light travels in a straight path called a ray, however, when passing through

transparent materials, like water or glass, light bends or turns. This is because different materials or mediums have different qualities. In each type of medium, whether it is air or water or glass, the wavelength of the light will change, but not the frequency. As a result, the direction and speed of the traveling light wave will change and the light will appear to bend or change directions. One example of refraction is a prism. Prisms are unique in that each color of light is refracted to a different angle. So it can take white light from the sun and send out light of various colors. Lenses use refraction to help us see things. Telescopes help us to see things far away and microscopes enable us to see very small things. Even glasses use refraction so that we can see everyday things more clearly.

Atomic structure

The atom is the basic building block for all matter in the universe. Atoms are extremely small and are made up of a few even smaller particles. The basic particles that make up an atom are electrons, protons, and neutrons. Atoms fit together with other atoms to make up matter. It takes a lot of atoms to make up anything. There are so many atoms in a single human body we won't even try to write the number here. Suffice it to say that the number is trillions and trillions (and then some more). There are different kinds of atoms based on the number of electrons, protons, and neutrons each atom contains. Each different kind of atom makes up an element. There are 92 natural elements and up to 118 when you count in man-made elements. Atoms last a long time, in most cases forever. They can change and undergo chemical reactions, sharing electrons with other atoms. But the nucleus is very hard to split, meaning most atoms are around for a long time.

Structure of the Atom At the center of the atom is the nucleus. The nucleus is made up of the protons and neutrons. The electrons spin in orbits around the outside of the nucleus.

The Proton The proton is a positively charged particle that is located at the center of the atom in the nucleus. The hydrogen atom is unique in that it only has a single proton and no neutron in its nucleus.

The Electron The electron is a negatively charged particle that spins around the outside of the nucleus. Electrons spin so fast around the nucleus, scientists can never be 100% sure where they are located, but scientists can make estimates of where electrons should be. If there are the same number of electrons and protons in an atom, then the atom is said to have a neutral charge. Electrons are attracted to the nucleus by the positive charge of the protons. Electrons are much smaller than neutrons and protons. About 1800 times smaller!

The Neutron The neutron doesn't have any charge. The number of neutrons affects the mass and the radioactivity of the atom.

Other (even smaller!) particles Quark - The quark is a really small particle that makes up neutrons and protons. Quarks are

nearly impossible to detect and it's only recently that scientists figured out they existed. They were discovered in 1964 by Murray Gell-Mann. There are 6 types of quarks: up, down, top, bottom, charm, and strange.

Neutrino - Neutrinos are formed by nuclear reactions. They are like electrons without any charge and are usually travelling at the speed of light. Trillions and trillions of neutrinos are emitted by the sun every second. Neutrinos pass right through most solids including humans!

Nuclear Physics

Nuclear energy is the energy stored inside an atom by the forces that hold together the nucleus of the atom. Scientists have learned how to capture large amounts of energy from these forces that can then be used to generate electricity. E = mc2 When working on his theory of relativity, Albert Einstein discovered the mathematical formula E = mc2. This formula demonstrated that matter could be converted into energy. Although this sounds like a simple concept, it demonstrated that a large amount of energy could be generated from a very small amount of matter. This could be done by splitting an atom in a process called nuclear fission.

Nuclear Fission Nuclear fission is the process of splitting of a large atom into two or more smaller atoms. When an atom is split a huge amount of energy is released. When the energy is released in a slow controlled manner, it can be used to generate electricity to power our homes. When the energy is released all at once, a chain reaction occurs causing a nuclear explosion.

Nuclear Power Plants One of the major applications for nuclear fission is nuclear power. Nuclear power plants use nuclear fission to generate heat. They use this heat to create steam from water which, in turn, powers electrical generators. Around twenty percent of the electricity in the United States is generated by nuclear power plants. There are 104 commercial nuclear generating units in the U.S. Nuclear power plants use the element uranium as fuel. Control rods of uranium are used to make sure that the chain reaction of atoms splitting proceeds at a controlled pace.

Radioactive Waste One of the byproducts of nuclear energy is radioactive waste. This is leftover material from the nuclear reaction. Radioactive material can be dangerous to humans and animal life.

Other Uses of Nuclear Power Nuclear power has other applications in addition to power plants. One application is nuclear propulsion in ships and submarines. Nuclear powered submarines can stay under water and travel at high speeds for a long time. Nuclear power has also been used in naval ships, ships used for breaking ice in the polar seas, and space ships. These ships of the U.S. Navy are nuclear powered Nuclear Fusion Another form of nuclear energy is nuclear fusion. Fusion occurs when two or more atoms are joined together to make a larger atom. Stars get their power from nuclear fusion. Deep inside a star, hydrogen atoms are constantly being converted by fusion into helium atoms. It's this process that generates the light and heat energy given off by the stars including the Sun. Scientists have not figured out how to control fusion to create usable energy. If they could it would be great news as fusion produces less radioactive material and would give us a virtually unlimited supply of energy. Interesting Facts about Nuclear Energy and Fission

The top three states for generating nuclear energy are Illinois, Pennsylvania, and South Carolina.

The United States generates more nuclear energy than any other nation. In the history of nuclear energy there have been three major nuclear power plant disasters

including Chernobyl (Russia), Three Mile Island (United States), and Fukushima Daiichi (Japan).

The first nuclear powered submarine was the U.S.S. Nautilus which put out to sea in 1954. One uranium pellet can generate the same amount of energy as around 1,000 kilograms of coal. The "smoke" you see coming from a nuclear power plant is not pollution, but steam.

Radioactivity

Stable and Unstable Isotopes Elements can be made up of different isotopes. Isotopes are atoms with the same number of protons and electrons, but a different number of neutrons. Sometimes isotopes are stable and happy. These are the elements that we see around us and find in nature. However, some isotopes are unstable. These isotopes are called radioactive isotopes. You can go here to learn more about isotopes.

What is radioactive decay? When isotopes are unstable they emit energy in the form of radiation. There are three main types of radiation or radioactive decay depending on the isotope.

Different Types of Radioactivity Alpha decay - Alpha decay is caused when there are too many protons in a nucleus. In this case the element will emit radiation in the form of positively charged particles called alpha particles. Beta decay - Beta decay is caused when there are too many neutrons in a nucleus. In this case the element will emit radiation in the form of negatively charged particles called beta particles. Gamma decay - Gamma decay occurs when there is too much energy in the nucleus. In this case gamma particles with no overall charge are emitted from the element.

How is it measured? Radioactivity is measured using a unit called the "curie". It is abbreviated as "Ci". The curie measures how many atoms spontaneously decay each second. The curie was named after Marie and Pierre Curie who discovered the element radium.

What is the half-life of an isotope? The half-life of an isotope is the time on average that it takes for half of the atoms in a sample to decay. For example, the half-life of carbon-14 is 5730 years. This means that if you have a sample of carbon-14 with 1,000 atoms, 500 of these atoms are expected to decay over the course of 5730 years. Some of the atoms may decay right away, while others will not decay for many thousands more years. The thing to remember about half-life is that it is a probability. In the example above, 500 atoms are "expected" to decay. This is not a guarantee for one specific sample. It is just what will happen on average over the course of billions and billions of atoms.

Radioactive Decay to other Elements When isotopes decay they can lose some of their atomic particles (i.e. electrons and protons) and turn from one element into another. Sometimes isotopes decay from one unstable isotope into another unstable isotope. This can happen continuously in a long radioactive chain. An example of a radioactive chain is uranium-238. As it decays, it transforms through a number of elements including thorium, radium, francium, radon, polonium, and bismuth. It finally ends up as a stable isotope as the element lead. Why is radiation dangerous? Is some radiation good?Radiation can alter the structure of cells in our bodies causing mutations which can produce cancer. The more radiation a person is exposed to, the more dangerous it is. Despite the risks, there are a number of good ways that science has used radiation. These include X-rays, medicine, carbon dating, energy generation, and to kill germs.

Interesting Facts about Radioactivity

Uranium in the ground can decay into radon gas which can be very dangerous to humans. It is thought to be the second leading cause of lung cancer.

The half-life of carbon-14 is used in carbon dating to determine the age of fossils. Bismuth is the heaviest element with at least one stable isotope. All elements heavier than

bismuth are radioactive. Radioactivity was discovered by the scientist A. H. Becquerel in 1896.