Earth

 

Your Blue Home

The third planet from the Sun is your home. The Earth is the only known planet where life can survive. As far as we know, there is no other planet in the universe like Earth. We have a very narrow temperature range that allows water to remain a liquid. Life has developed over millions of years because of that liquid. What else makes us special? Most of our atmosphere is made of nitrogen (N), a relatively inert gas. If we had clouds of sulfuric acid or methane (like other planets), life may have never developed.

A Surface That Floats

There are also huge landmasses on our planet. The rock plates that float across the surface are called tectonic plates. Those plates float on the liquid region called the mantle. The mantle is an area between the core and the crust that is filled with molten rock. It is kept in a liquid state because of the energy given off by the center (core) of the Earth. Scientists have also discovered that pressure increases as you move towards the center of the planet. The core of the Earth has extreme temperatures and pressures that keep the iron (Fe) and other metals liquid and flowing.

Magnetic Field Armor

Flowing metal in our planet helps create something called a dynamo effect. Dynamos create large magnetic fields. In the case of the Earth, the magnetic field protects our planet from space. This protective cover is called the magnetosphere. It shields us from the solar winds and solar radiation. You can see where solar winds and the magnetosphere collide when you see the Aurora Borealis (northern hemisphere) and the Aurora Australis (southern hemisphere).

Built For Life

Although many planets in the Solar System have atmospheres, ours protects us from space and encourages life. With an atmosphere made up of 78% nitrogen (N), 21% oxygen (O), and 0.03% carbon dioxide (CO2), life has thrived on this planet. Our atmosphere has many layers divided by different temperatures and pressures. The atmosphere also provides the planet with protection. The ozone (O3) that surrounds Earth filters out ultra-violet light. The density (thickness) of the atmosphere helps to vaporize many solid particles colliding with the planet. As you can tell, the atmosphere serves many purposes.

Solar System

 

More Than Planets

If you finished the main Solar System section, you now understand that our system has one star and eight accepted planets. Given that basic information, we want to let you know that there is much more in our little system than those nine objects.

What You Can See

Sure, you can see a planet. They are tough to miss. As you continue exploring, you will find moons around almost every planet. While the Earth only has one, other planets have more than twenty moons. You also know that you can see rings made of small pieces of dust and ice that circle Saturn and other gas giants.

As you look for smaller objects in the system, you will find a field of asteroids in orbit around the Sun between Mars and Jupiter. There are also stray asteroids flying through the Solar System. Comets are also found orbiting the Sun. The amazing thing is that there may still be other objects in our Solar System. That's one of the exciting things about astronomy... There are still millions of things to discover in the universe.

What You Can't See

There are also many things we can't see in the Solar System. There are small particles and energies swirling throughout the system. Many of these unseen energies are created by the Sun. We have a heliosphere that surrounds our entire system and Voyager has just reached the heliopause (the edge). The Sun also gives off small particles called the solar wind, light, and various types of radiation. While Earth needs to be protected from some of these forces, the energy that creates the heliosphere is protecting every object in our system.

 

Mechanics and Motion

Motion is one of the key topics in physics. Everything in the universe moves. It might only be a small amount of movement and very very slow, but movement does happen. Don't forget that even if you appear to be standing still, the Earth is moving around the Sun, and the Sun is moving around our galaxy. The movement never stops. Motion is one part of what physicists call mechanics. Over the years, scientists have discovered several rules or laws that explain motion and the causes of changes in motion. There are also special laws when you reach the speed of light or when physicists look at very small things like atoms.

Speed it Up, Slow it Down

The physics of motion is all about forces. Forces need to act upon an object to get it moving, or to change its motion. Changes in motion won't just happen on their own. So how is all of this motion measured? Physicists use some basic terms when they look at motion. How fast an object moves, its speed or Velocity, can be influenced by forces. (Note: Even though the terms 'speed' and 'velocity' are often used at the same time, they actually have different meanings.)

Acceleration is a twist on the idea of velocity. Acceleration is a measure of how much the velocity of an object changes in a certain time (usually in one second). Velocities could either increase or decrease over time. Mass is another big idea in motion. Mass is the amount of something there is, and is measured in grams (or kilograms). A car has a greater mass than a baseball.

Simple and Complex Movement

There are two main ideas when you study mechanics. The first idea is that there are simple movements, such as if you're moving in a straight line, or if two objects are moving towards each other in a straight line. The simplest movement would be objects moving at constant velocity. Slightly more complicated studies would look at objects that speed up or slow down, where forces have to be acting.

There are also more complex movements when an object's direction is changing. These would involve curved movements such as circular motion, or the motion of a ball being thrown through the air. For such complex motions to occur, forces must also be acting, but at angles to the movement.

In order to really understand motion, you have to think about forces, acceleration, energy, work, and mass. These are all a part of mechanics.

Motion Glossary and Terms

 

Motion Glossary and Terms

Acceleration - Acceleration is the measurement of the change in an object's velocity. It is equal to the change in velocity over the change in time. Acceleration is a vector. 

Collision - A collision in physics occurs when any two objects bump into each other. 

Displacement - In physics, displacement refers to an object's overall change in position. It is a vector quantity.

 Energy - Energy is the ability to do work. The standard unit of measure for energy is the joule. 

First law of motion - The first law of motion states that any object in motion will continue to move in the same direction and speed unless external forces act on it.

 Force - Force is the measurement of a push or pull on an object. Force is a vector measured in newtons.

 Friction - Friction is the resistance of motion when one object rubs against another. It is a force and is measured in newtons.

Gravity - Gravity is a force caused when the mass of physical bodies attract each other. On Earth gravity pulls at objects with an acceleration of 9.8 m/s2. 

Impulse - An impulse is a change in momentum. 

Joule - The joule is the standard unit of measure for energy and work. 

Kinetic energy - Kinetic energy is the energy an object has due to its motion. It is a scalar quantity calculated using the formula KE = ½ * m * v2, where m = mass and v = velocity.

Mass - Mass is a measurement of how much matter is in an object. It is usually measured in kilograms. 

Momentum - Momentum is a measurement of mass in motion. Momentum is equal to the mass times the velocity of an object. It is a vector measured in newton-seconds. 

Newton - The newton is the standard unit of measure for force. Pascal - The pascal is the standard unit of measure for pressure. 

Potential energy - Potential energy is the energy stored by an object due to its state or position. It is measured in joules. Power - Power is a measurement of the rate at which energy is used. Power is calculated by dividing work over time. The standard unit for power is the watt. 

Pressure - Pressure is the force over a given area. Pressure is measured in pascals. 

Scalar - A scalar is a measurement that only measures the magnitude. Unlike a vector, a scalar does not have direction. Second law of motion - The second law of motion states that the greater the mass of an object, the more force it will take to accelerate the object. 

Simple machine - A simple machine is a basic mechanical device for applying a force and doing work. Some examples of simple machines include the lever, pulley, inclined plane, wedge, and screw. 

Speed - Speed is the measurement of how fast on object moves relative to a reference point. It is a scalar quantity measured by distance over time. 

Third law of motion - The third law of motion states that for every action there is an equal and opposite reaction. 

Vector - A vector is a quantity that has both a magnitude and a direction. 

Velocity - Velocity is the rate of change in an object's position. Velocity is a vector quantity. The magnitude of velocity is the object's speed. 

Watt - The watt is the standard unit of measure for power. Weight - Weight is the force of gravity on an object. In physics, weight is measured in newtons. 

Work - Work occurs in physics when a force acts on an object to move it some distance. Work is equal to the force times the distance and is measured in joules.

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What Is Time?

 WHAT IS TIME?

Time is familiar to everyone, yet it's hard to define and understand. Science, religion, philosophy, and the arts have different definitions of time, but the system of measuring it is relatively consistent.Clocks are based on seconds, minutes, and hours. While the basis for these units has changed throughout history, they trace their roots back to ancient Sumeria. The modern international unit of time, the second, is defined by the electronic transition of the cesium atom. But what, exactly, is time? Physicists define time as the progression of events from the past to the present into the future. Basically, if a system is unchanging, it is timeless. Time can be considered to be the fourth dimension of reality, used to describe events in three-dimensional space. It is not something we can see, touch, or taste, but we can measure its passage. 

Physics equations work equally well whether time is moving forward into the future (positive time) or backward into the past (negative time.) However, time in the natural world has one direction, called the arrow of time. The question of why time is irreversible is one of the biggest unresolved questions in science.

One explanation is that the natural world follows the laws of thermodynamics. The second law of thermodynamics states that within a closed system, the entropy of the system remains constant or increases. If the universe is considered to be a closed system, its entropy (degree of disorder) can never decrease. In other words, the universe cannot return to exactly the same state in which it was at an earlier point. Time cannot move backward.As far as the universe is concerned, time had a beginning. The starting point was 13.799 billion years ago when the Big Bang occurred. We can measure cosmic background radiation as microwaves from the Big Bang, but there isn't any radiation with earlier origins. One argument for the origin of time is that if it extended backward infinitely, the night sky would be filled with light from older stars.

Will time end? The answer to this question is unknown. If the universe expands forever, time would continue. If a new Big Bang occurs, our time line would end and a new one would begin. In particle physics experiments, random particles arise from a vacuum, so it doesn't seem likely the universe would become static or timeless. Only time will tell.