Mechanics

 

Mechanics

Mechanics is generally taken to mean the study of the motion of objects (or their lack of motion) under the action of given forces. Classical mechanics is sometimes considered a branch of applied mathematics. It consists of kinematics, the description of motion, and dynamics, the study of the action of forces in producing either motion or static equilibrium (the latter constituting the science of statics). The 20th-century subjects of quantum mechanics, crucial to treating the structure of matter, subatomic particles, superfluidity, superconductivity, neutron stars, and other major phenomena, and relativistic mechanics, important when speeds approach that of light, are forms of mechanics that will be discussed later in this section.

In classical mechanics the laws are initially formulated for point particles in which the dimensions, shapes, and other intrinsic properties of bodies are ignored. Thus in the first approximation even objects as large as Earth and the Sun are treated as pointlike—e.g., in calculating planetary orbital motion. In rigid-body dynamics, the extension of bodies and their mass distributions are considered as well, but they are imagined to be incapable of deformation. The mechanics of deformable solids is elasticity; hydrostatics and hydrodynamics treat, respectively, fluids at rest and in motion.

The three laws of motion set forth by Isaac Newton form the foundation of classical mechanics, together with the recognition that forces are directed quantities (vectors) and combine accordingly. The first law, also called the law of inertia, states that, unless acted upon by an external force, an object at rest remains at rest, or if in motion, it continues to move in a straight line with constant speed. Uniform motion therefore does not require a cause. Accordingly, mechanics concentrates not on motion as such but on the change in the state of motion of an object that results from the net force acting upon it. Newton’s second law equates the net force on an object to the rate of change of its momentum, the latter being the product of the mass of a body and its velocity. Newton’s third law, that of action and reaction, states that when two particles interact, the forces each exerts on the other are equal in magnitude and opposite in direction. Taken together, these mechanical laws in principle permit the determination of the future motions of a set of particles, providing their state of motion is known at some instant, as well as the forces that act between them and upon them from the outside. From this deterministic character of the laws of classical mechanics, profound (and probably incorrect) philosophical conclusions have been drawn in the past and even applied to human history.

Lying at the most basic level of physics, the laws of mechanics are characterized by certain symmetry properties, as exemplified in the aforementioned symmetry between action and reaction forces. Other symmetries, such as the invariance (i.e., unchanging form) of the laws under reflections and rotations carried out in space, reversal of time, or transformation to a different part of space or to a different epoch of time, are present both in classical mechanics and in relativistic mechanics, and with certain restrictions, also in quantum mechanics. The symmetry properties of the theory can be shown to have as mathematical consequences basic principles known as conservation laws, which assert the constancy in time of the values of certain physical quantities under prescribed conditions. The conserved quantities are the most important ones in physics; included among them are mass and energy (in relativity theory, mass and energy are equivalent and are conserved together), momentum, angular momentum, and electric charge.

physics science

 

physics

science

 

Physics, science that deals with the structure of matter and the interactions between the fundamental constituents of the observable universe. In the broadest sense, physics (from the Greek physikos) is concerned with all aspects of nature on both the macroscopic and submicroscopic levels. Its scope of study encompasses not only the behaviour of objects under the action of given forces but also the nature and origin of gravitational, electromagnetic, and nuclear force fields. Its ultimate objective is the formulation of a few comprehensive principles that bring together and explain all such disparate phenomena.

Physics is the basic physical science. Until rather recent times physics and natural philosophy were used interchangeably for the science whose aim is the discovery and formulation of the fundamental laws of nature. As the modern sciences developed and became increasingly specialized, physics came to denote that part of physical science not included in astronomy, chemistry, geology, and engineering. Physics plays an important role in all the natural sciences, however, and all such fields have branches in which physical laws and measurements receive special emphasis, bearing such names as astrophysics, geophysics, biophysics, and even psychophysics. Physics can, at base, be defined as the science of matter, motion, and energy. Its laws are typically expressed with economy and precision in the language of mathematics.

Both experiment, the observation of phenomena under conditions that are controlled as precisely as possible, and theory, the formulation of a unified conceptual framework, play essential and complementary roles in the advancement of physics. Physical experiments result in measurements, which are compared with the outcome predicted by theory. A theory that reliably predicts the results of experiments to which it is applicable is said to embody a law of physics. However, a law is always subject to modification, replacement, or restriction to a more limited domain, if a later experiment makes it necessary.

Visible Light Waves

Visible Light Waves

 

 

Types of Light

To understand light you have to know that what we call light is what is visible to us. Visible light is the light that humans can see. Other animals can see different types of light. Dogs can see only shades of gray and some insects can see light from the ultraviolet part of the spectrum. The key thing to remember is that our light is what scientists call visible light.

Scientists also call light electromagnetic radiation. Visible light is only one small portion of a family of waves called electromagnetic (EM) radiation. The entire spectrum of these EM waves includes radio waves, which have very long wavelengths and both gamma rays and cosmic rays, which are at the other end of the spectrum and have very small wavelengths. Visible light is near the middle of the spectrum.

It's all Energy

The key thing to remember is that light and EM radiation carry energy. The quantum theory suggests that light consists of very small bundles of energy/particles; it's just that simple. Scientists call those small particles photons, and the wavelength determines the energy and type of EM radiation, and the number of photons tells you how much radiation there is. A lot of photons give a brighter, more intense type of light. Fewer photons give a very dim and less intense light. When you use the dimmer switch on the wall, you are decreasing the number of photons sent from the light bulb. The type of light is the same while the amount has changed.

Different Speeds of Light?

As far as we know, all types of light move at one speed when in a vacuum. The speed of light in a vacuum is 299,792,458 meters per second. That speed is really fast, but even when you're traveling that fast, it takes a while to get places in space. It takes about seven minutes for light from the Sun to reach Earth. It takes over four years for the light from our Sun to get to the nearest star. It would take a particle of light over 100,000 years to get from one side of our galaxy to the other side. All of those values are light moving through a vacuum. You can slow light down in other substances such as the atmosphere, water, or a diamond. Light moves at about 124,000,000 meters per second (less than half the speed in a vacuum) in a diamond.

Communications

 

Communications

One of the great changes to our world over the past 100 years has been the invention of electronic communications. It all started with the telegraph and since then new inventions and innovations have created an information age that includes smart phones and high definition video over the internet.

Telegraph

The invention that got electronic communications started was the telegraph. It was invented by Samuel Morse in 1836. He also developed the Morse Code which allowed the signals that the telegraph sent over the wires to represent words and phrases.

Telephone

Around 40 years after the telegraph, Alexander Graham Bell received the patent for the telephone. Now instead of just beeps of sound, a person's voice could be transmitted over long distances of electric wires. Later inventions like faxes and modems would allow other information to pass over the same wires. Large switching networks were built throughout the world allowing telephones in nearly every home to connect with each other.

Fiber optic tubes of glass use light pulses to communicate

Fiber Optics

As the amount of information has grown, more and more data needs to be transmitted over long distances. One of the ways to send data faster is with fiber optics. Fiber optics are long skinny tubes (like wires) made of glass. Instead of electricity they transmit light. Light can travel at much faster speeds and over longer distances than electrical pulses. There are fiber optic connections today that can send 100 billion signals per second!

Radio Frequency

Radios have been used for a long time, but in the 1990s cell phones started to become popular. Cell phones send information using radio frequencies through the air. New technologies have allowed for faster signals and even video to be sent to and from cell phones.

Cell phones use radio frequencies to communicate through the air

Internet

Perhaps the most important invention in the area of electronic communications during recent times is the internet. The internet is made up of millions of electrical and fiber optic links. These links form a network that allows information to get passed and "switched" all over the world. More information is now available at your fingertips and on your computer at home than you could hope to read in a lifetime.

Fun facts about Electronic Communications

• There are around 250 billion emails sent every day. Around 80% of these are spam.
• Around 20 hours of video are uploaded to YouTube every minute.
• Fiber optics are good because they use less energy and are better for the environment than electrical wires. They are also very resistant to weather.
• The first telephone pole was built in 1876.
• There are over 4 billion cell phones in the world. Over 100 million cell phones are thrown away every year.
• The first cell phone was invented by the company Motorola.

Digital Electronics

 

Digital Electronics

Digital electronics are electric circuits that work on only two fixed values: "1" and "0". They use a series of 1's and 0's to store and communicate information. They can also perform math using just 1's and 0's. This is called Boolean math or Boolean logic.

How do they get just 1's and 0's?

In most digital electronic circuits when the voltage of the circuit is positive and near the supply voltage it represents a 1. This is also called HIGH. When the voltage is close to the ground level (or zero), it represents a 0, which is also sometimes called LOW. With these two signals most anything can be stored and communicated including the picture on the screen you're looking at right now. But it takes a LOT of these signals running VERY fast!

What are electronic gates?

In digital electronics, gates are electrical functions that are performed on 1's and 0's. Sort of like simple math. One example of this is the AND gate. There are two inputs and one output to an AND gate. The output is only a 1 if both inputs are a 1. If either input is a 0, the output is a 0. An even simpler gate is the Inverter. In this case there is one input and one output. If a 1 is input, then a 0 is output. If a 0 is input then a 1 is output. It just Inverts the signal.

A logic AND gate with two inputs and one output

What are electronic chips?

Electronic chips are a whole bunch of electronic gates put into one small area. These chips can have millions and millions of gates in order to do all sorts of complex stuff. There are chips that do graphics for your computer screen, chips that have lots of memory for saving data, and chips that run programs like your computer's CPU. To make electronic chips, special materials called semiconductors are used together with expensive precision equipment. Hundreds of engineers may spend years just to design and invent one complex electronic chip.

Integrated Circuit computer chip called a CPU

Where are they used?

Digital electronics are used throughout the world including in computers, iPods, video games, televisions, cameras, cell phones, and cars. Although digital electronics are a relatively new invention in the world, most of us could hardly imagine a world without them.

Fun facts about Digital Electronics

• The main semiconductor used in electronic chips is silicon. Silicon is the most abundant element in the Earth's crust after oxygen.
• A lot of the internet information is sent over fiber optics. With fiber optics light is used instead of electricity to send the information.
• The first computer chip was invented by Jack Kilby while working for the company Texas Instruments.
• In 2011 Apple became the largest buyer of computer chips in the world because of the iPhone.

Electricity in Nature

 

Electricity in Nature

Electricity is not only found in power lines and electronics made by man, but is also found in nature. In fact electricity is all around us. We see it in lightning storms, animals use it as a defense, even our bodies use it to send messages to our muscles.

Lightning

One of the most fantastic displays of electricity in nature is lightning. Lightning occurs when large amounts of electrostatic energy builds up in clouds from the energy of storms. When electrically charged regions of clouds discharge their energy, a large flash of electricity can be seen in the sky. Lightning may occur from cloud to cloud or it can occur from cloud to the ground. Lightning strikes carry huge amounts of energy. A typical lightning strike carries an electric current of over 30,000 amps and delivers 500 megajoules of energy.

Lightning also creates a loud noise called thunder. This is because the air within lightning gets so hot, that it transforms into plasma for a short period of time. When the molecules of air turn from gas to plasma, their expansion causes a shockwave that we hear as thunder.

Animals

Some animals use electricity to survive in nature. Many of these animals are found in the ocean where some use electricity to detect objects around them (sort of like seeing) and others use electricity to fend off predators or even hunt for food.

One of the most famous of the electric animals is the electric eel. The electric eel can produce large amounts of electricity, enough to even kill a human or stun a large horse. The eels typically swim into a school of fish, discharge a large amount of electricity, and then dinner is served!

Another example of animals using electricity is electroreception. Many fish such as sharks, lampreys, and catfishes have the ability to generate electric fields and then use these fields to detect objects around them. This helps them to "see" in dark areas and to sense hidden prey.

Human Body

Not only can we see electricity at work in nature, we are constantly using electricity in our bodies. Every time we move a muscle, it's the result of an electrical signal being sent from our brain to our muscles telling them to move. We actually have a complex system of nerves throughout our bodies that use electric signals to control everything we do.

Static Electricity

Lightning isn't the only form of electrostatic energy we see in nature. Static electricity charges build up all around us. You probably have noticed static electricity when you went down a slide at the park and your hair stood up strait. The friction from the slide on your body caused a build up of charge that made your hair stand up. Sometimes you can even build up a charge on your body that will shock someone else when you touch them. This is static electricity.

The Earth

Deep inside the Earth huge electric currents are generated from the spin of the Earth's iron core. These electric currents in turn cause a magnetic field that extends well beyond the surface of the Earth and into outer space.

The Earth's magnetic field is important because it protects the Earth from the solar wind of the Sun. Without the protection of magnetic field, there would likely be no life on Earth. The magnetic field also enables the use of compasses to tell the direction.