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Forces are a big part of physics. Physicists devote a lot of time to the study of forces that are found everywhere in the universe. The forces could be big, such as the pull of a star on a planet. The forces could also be very small, such as the pull of a nucleus on an electron. Forces are acting everywhere in the universe at all times.

If you were a ball sitting on a field and someone kicked you, a force would have acted on you. As a result, you would go bouncing down the field. There are often many forces at work. Physicists might not study them all at the same time, but even if you were standing in one place, you would have many forces acting on you. Those forces would include gravity, the force of air particles hitting your body from all directions (as well as from wind), and the force being exerted by the ground (called the normal force).

Let's look at the forces acting on that soccer ball before you kicked it. As it sat there, the force of gravity was keeping it on the ground, while the ground pushed upward, supporting the ball. On a molecular level, the surface of the ball was holding itself together as the gas inside of the ball tried to escape. There may have also been small forces trying to push it as the wind blew. Those forces were too small to get it rolling, but they were there. And you never know what was under the ball. Maybe an insect was stuck under the ball trying to push it up. That's another force to consider.

If there is more than one force acting on an object, the forces can be added up if they act in the same direction, or subtracted if they act in opposition. Scientists measure forces in units called Newtons. When you start doing physics problems in class, you may read that the force applied to the soccer ball (from the kick) could be equal to 12 Newtons.

There is one totally important formula when it comes to forces, F = ma. That's all there is, but everything revolves around that formula. "F" is the total (net) force, "m" is the object's mass, and "a" is the acceleration that occurs. As a sentence, "The net force applied to the object equals the mass of the object multiplied by the amount of its acceleration." The net force acting on the soccer ball is equal to the mass of the soccer ball multiplied by its change in velocity each second (its acceleration). Do you remember the wind gently blowing on the soccer ball? The force acting on the ball was very small because the mass of air was very small. Small masses generally exert small forces, which generally result in small accelerations (changes in motion).

We cover the details of vectors on another page. A vector can be used to represent any force. A force vector describes a specific amount of force that is applied in a specific direction. If you kick that soccer ball with the same force, but in different directions, and you get different results...

Or search the sites for a specific topic.

Real World: Centripetal Force (NASA-eClips Video)

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Physics4Kids.com! This tutorial introduces forces in physics. Other sections include modern physics, heat, electricity, magnetism, and light.

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We use the concept of energy to help us describe how and why things behave the way they do. We talk about solar energy, nuclear energy, electrical energy, chemical energy, etc. If you apply a force to an object, you may change its energy. That energy must be used to do work, or accelerate, an object. Energy is called a scalar; there is no direction to energy (as opposed to vectors). We also speak of kinetic energy, potential energy, and energy in springs. Energy is not something you can hold or touch. It is just another means of helping us to understand the world around us. Scientists measure energy in units called joules.

Kinetic and potential energies are found in all objects. If an object is moving, it is said to have kinetic energy (KE). Potential energy (PE) is energy that is "stored" because of the position and/or arrangement of the object. The classic example of potential energy is to pick up a brick. When it's on the ground, the brick had a certain amount of energy. When you pick it up, you apply force and lift the object. You did work. That work added energy to the brick. Once the brick is in a higher/new position, we would say that the increased energy was stored in the brick as PE. Now the brick can do something it couldn't do before; it can fall. And in falling, can exert forces and do work on other objects.

The study of springs is a whole section of physics. A spring that just sits there doesn't do much. When you push on it, you exert a force and change the arrangement of the coils. That change in the arrangment stores energy in the spring. It now contains energy and can expand and do work on other things. Anything that is elastic (can change its arrangement and then restore itself), such as a rubber band, can store energy in the same way.

A rubber band can be stretched and then it is ready to do something. That stretching involves work and increases the potential energy. You can flatten a solid rubber ball and it will want to bounce back up. You can also pull the drawstring of a bow and the work done stores the energy that can make the arrow go flying. Those are all examples of your putting energy in, and then something happening when the energy comes out.

Gases? What can they do? Gases are great because they can compress and expand. They act as if they were elastic. If the pressure increases and compresses gas molecules, the amount of stored energy increases. It's similar to a spring, but slightly different. Eventually that energy in the compressed gas can be let out to do something (work).

In your car, there are shock absorbers. Some shocks have compressed gas in the cylinders rather than springs. The energy in those cylinders keeps your car from bouncing too much in potholes. Think about wind. Wind is caused because of pressure differences in the atmosphere. When the wind blows it can do anything - turn windmills, help birds fly, make tornadoes, and do all types of work.

Or search the sites for a specific topic.

Law of Conservation of Energy (NASA-eClips Video)

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Physics4Kids.com: Motion: Energy of Motion

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Physics4Kids.com! This tutorial introduces the physics of energy in motion. Other sections include modern physics, heat, electricity, magnetism, and light.

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Physics4Kids.com! This tutorial introduces the physics of velocity. Other sections include modern physics, heat, electricity, magnetism, and light.

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8th Grade Science Final Topics 17-18 PDF.pdf

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Khan Academy

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Endothermic vs. exothermic reactions (article) | Khan Academy

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Interactive

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How To instructions

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A force diagram is simply a diagram showing all the forces acting on an object, the force's direction and its magnitude. It is a simplification of the picture that shows just the forces. In the example below, the first image is a picture of a climber on the side of a cliff.

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Chart

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Video

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Copyright © 2017 Discovery Education. All rights reserved. Discovery Education is a subsidiary of Discovery Communications, LLC.

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Bill Nye

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Song

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I'm Atoms (Scientific Cover of Jason Mraz's I'm Yours)

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Well an atom's made of protons, neutrons, and electrons the first two in the nucleus, the third around it it's mostly empty space, but it feels solid in any case The elements are all the different types of atoms they differ by the number of protons in the middle.

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Speed, velocity and acceleration. Video Clip

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Motion in a Straight Line: Crash Course Physics #1

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Reading- Click on all pages!

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Chem4Kids

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Chem4Kids.com! This tutorial introduces basics of chemical reactions. Other sections include matter, elements, the periodic table, and biochemistry.

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Reading

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BBC Bitesize - KS3 Physics - Physical changes - Revision 4

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Learn about the physical changes that take place in solids, liquids and gases with BBC Bitesize KS3 Science.

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Diagram

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Particle Diagram

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StudyJams video clip

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Changes of Matter: StudyJams! Science | Scholastic.com

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Matter has many ways of changing its properties. This StudyJams! activity will teach students all about the ways in which matter can change.

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Slides

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Physical & Chemical Changes - Lessons - Tes Teach

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Video demonstration

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chemical change physical change property chem

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A short exploration of physical changes in ma

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Video lesson

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Physical vs Chemical Properties - Explained

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Reading

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Magnesium reacts with oxygen from the air producing an extremely bright flame. This is a chemical change since magnesium oxide has completely different properties than magnesium metal shown on the left. Safety: Do not try this without supervision and DO NOT LOOK DIRECTLY AT THE LIGHT!

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Reading

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A physical change takes place without any changes in molecular composition. The same element or compound is present before and after the change. The same molecule is present through out the changes. Physical changes are related to physical properties since some measurements require that changes be made.

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Diagram

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Can you tell the difference? Reading

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Elements and compounds are pure chemical substances found in nature. The difference between an element and a compound is that an element is a substance made of same type of atoms, whereas a compound is made of different elements in definite proportions. Examples of elements include iron, copper, hydrogen and oxygen. Examples of compounds include water (H ₂ O) and salt (Sodium Chloride - NaCl)

Elements are listed according to their atomic number on the Periodic Table. Among the 117 known elements, 94 are naturally occurring like carbon, oxygen, hydrogen etc. 22 are artificially produced having undergone radioactive changes. The reason for this is their instability due to which they undergo radioactive decay over a period of time giving rise to new elements during the process like Uranium, Thorium, Bismuth etc. Elements combine in fixed ratios and give rise to stable compounds due to chemical bonds that facilitate compound formation.

Differences in Properties

Elements are distinguished by their name, symbol, atomic number, melting point, boiling point, density and ionization energies. In the Periodic Table, elements are arranged according to their atomic number and they are grouped according to similar chemical properties and are depicted by their symbols.

Atomic number - the atomic number is denoted by the letter Z and is the number of protons present in the nucleus of the atom of element. For e.g. carbon has 6 protons in its nucleus and for Carbon, Z = 6. Number of protons is also indicative of electric charge or number of electrons present in the nucleus which determines chemical properties of the element.

Atomic Mass - the letter A indicates the atomic mass of the element which is the total number of protons and neutrons in the nucleus of an atom of the element. Isotopes of the same elements differ in their atomic masses.

Isotopes - isotopes of an element have the same number of protons in their nucleus but differ in the number of neutrons. Naturally occurring elements have more than one stable isotope. Thus isotopes have similar chemical properties (due to same number of protons) but different nuclear properties (due to different number of neutrons). For e.g. carbon has three isotopes, Carbon - 12, Carbon -13 and Carbon - 14.

Allotropes - atoms of an element can form bonds with each other in more than one way leading to difference in their chemical properties. For e.g. carbon binds in a tetrahedron to form diamond and layers of hexagons of carbon forms graphite.

Compounds are composed of different elements in a fixed proportion. For example, 1 atom of sodium (Na) combines with 1 atom of chlorine (Cl) to form one molecule of sodium chloride (NaCl) compound. The elements in a compound do not always retain their original properties and cannot be separated by physical means. The combining of elements is facilitated by their valency. Valency is defined as the number of hydrogen atoms required that can combine with an atom of the element forming the compound. Most compounds can exist as solids (low enough temperatures) and can be decomposed by the application of heat. Sometimes foreign elements are trapped inside crystal structure of compounds giving them a non homogeneous structure. Compounds are depicted by their chemical formula which follows the Hill system wherein carbon atoms are listed first, followed by hydrogen atoms after which elements are listed in alphabetical order.

History of Elements and Compounds

Elements were initially used as a reference to any state of matter like liquid, gas, air, solid etc. Indian, Japanese and Greek traditions refer to five elements namely, air, water, earth, fire and aether. Aristotle conceptualized a new fifth element called 'quintessence' - which apparently formed the heavens. As research continued, many eminent scientists paved way for the current understanding and description of elements. Among them, work of Robert Boyle, Antoine Lavoisier, Dmitri Mendeleev are particularly notable. Lavoisier was the first to make a list of chemical elements and Mendeleev was the first to arrange elements according to their atomic number in the Periodic Table. The most current definition of an element is awarded by the studies carried out by Henry Moseley which states that the atomic number of an atom is expressed physically by its nuclear charge.

Before the 1800s the usage of term compound could also mean a mixture. It was in the 19th century that meaning of a compound could be distinguished from a mixture. Alchemists like Joseph Louis Proust, Dalton and Berthollet and their studies on various compounds have given modern chemistry the current definition of compound. Proust's work demonstrated to the world of chemistry that compounds were made constant composition of respective elements.

CAS Number

Every chemical substance is identified by its unique numerical identifier - the CAS (chemical abstracts service) number. Hence every chemical compound and element has a CAS number. This makes database searches for elements and compounds more convenient.

References

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What's the difference between Compound and Element? Elements and compounds are pure chemical substances found in nature. The difference between an element and a compound is that an element is a substance made of same type of atoms, whereas a compound is made of different elements in definite proportions. E...

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Can you tell the difference? Video

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Atoms, elements, compounds & mixtures explained.

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A simple explanation of atoms, elements, compounds and mixtures using lego.

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Mixtures are not compounds...

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Kids learn about chemical mixtures in chemistry including solutions, alloys, suspensions, colloids, dissolving, examples, and facts.

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Definition

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Kid's learn about the science of chemical elements. Basic forms of matter made from a single type of atom.

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Multiple pages...make sure you click through all!

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BBC Bitesize - KS3 Chemistry - Atoms, elements and compounds - Revision 1

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Learn about the differences between atoms, elements and compounds with BBC Bitesize KS3 Science.

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Reading molecular formulas

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BBC Bitesize - KS3 Chemistry - Atoms, elements and compounds - Revision 4

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Learn about the differences between atoms, elements and compounds with BBC Bitesize KS3 Science.

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Difference between an atom and a molecule

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What's the Difference between an Atom and a Molecule?

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Parts

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Video Clip - LEGOS, remember??

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A review of elements, molecules, and elements using the LEGO molecule assignment metaphor.

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Chem4Kids

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Let's start with molecules. Molecule is the general term used to describe any atoms that are connected by chemical bonds. Every combination of atoms is a molecule. A compound is a molecule made of atoms from different elements. All compounds are molecules, but not all molecules are compounds. Hydrogen gas (H ₂) is a molecule, but not a compound because it is made of only one element. Water (H ₂ O) can be called a molecule or a compound because it is made of hydrogen (H) and oxygen (O) atoms.

There are two main types of chemical bonds that hold atoms together: covalent and ionic/electrovalent bonds. Atoms that share electrons in a chemical bond have covalent bonds. An oxygen molecule (O ₂) is a good example of a molecule with a covalent bond. Ionic bonds occur when electrons are donated from one atom to another. Table salt (NaCl) is a common example of a compound with an ionic bond.

You may also learn about a third type of bond. Metallic bonds occur between metal atoms. We're going to focus on ionic and covalent bonds.

When we discuss phase changes in matter, we are looking at physical changes. Physical forces alone (unless you're inside of the Sun or something extreme) rarely break down compounds completely. You can apply heat to melt an ice cube, but there will be no change in the water molecules. You can also place a cup of water in a container and decrease the pressure. The water will eventually boil, but the molecules will not change.

Chemical changes in compounds happen when chemical bonds are created or destroyed. Forces act on the bonds between atoms, changing the molecular structure of a substance. You can pour liquid acid on a solid and watch the solid dissolve. That process is a chemical change because molecular bonds are being created and destroyed. Geologists pour acids on rocks to test for certain compounds.

There are millions of different compounds around you. Probably everything you can see is one type of compound or another. When elements join and become compounds, they lose many of their individual traits. Sodium (Na) alone is very reactive. But when sodium and chlorine (Cl) combine, they form a non-reactive substance called sodium chloride (table salt, NaCl). New compounds have few or none of the physical or chemical traits of the original elements. They have a new life of their own.

If you look at sodium chloride, it is held together by one ionic/electrovalent bond. What about magnesium chloride (MgCl ₂)? It contains one magnesium (Mg) and two chlorine (Cl) atoms. There are two ionic bonds. Methane (CH ₄) is made up of one carbon (C) and four hydrogen (H) atoms. There are four bonds and they are all covalent.

Those examples have very simple chemical bonds. However, most compounds have combinations of ionic and covalent bonds. Let's look at sodium hydroxide (Na-OH)...

You can see the sodium (Na) part on the left and the hydroxide (-OH) part on the right. The bond that binds the hydrogen (H) to the oxygen (O) is covalent. The sodium is bonded to the hydroxide part of the compound with an ionic bond. This is a good example of how there can be different types of bonds within one compound.

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Chem4Kids.com! This tutorial introduces chemical compounds. Other sections include matter, elements, the periodic table, reactions, and biochemistry.

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Diagram

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Structure- Interactive

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In this interactive activity from ChemThink, learn about atomic structure. Follow the tutorial to understand how individual atoms-the basis of all matter-are composed of subatomic particles such as electrons, protons, and neutrons. Investigate the three types of particles, their properties (such as mass and charge), and relative locations.

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Size

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Jon Bergmann: Just how small is an atom?

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Just how small are atoms? Really, really, really small. This fast-paced animation from TED-Ed uses metaphors (imagine a blueberry the size of a football stadium!) to give a visceral sense of just how small atoms are. Lesson by Jon Bergmann, animation by Cognitive Media.

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History of the Atomic Model

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Atomos: Not to Be Cut The History of Atomic Theory

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Structure diagram

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Chem4Kids

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Atoms are the foundation of chemistry. They are the basis for everything in the Universe. As you know, matter is composed of atoms. Solids are made of densely packed atoms while gases have atoms that are spread out. We're going to cover basics like atomic structure and bonding between atoms. As you learn more, you can move to the reactions and biochemistry pages and see how atoms form compounds that help the biological world survive.

Are there pieces of matter that are smaller than atoms? Sure there are. Super-small particles can be found inside the pieces of atoms. These subatomic particles include nucleons and quarks. Nuclear chemists and physicists work together at particle accelerators to discover the presence of these tiny, tiny, tiny pieces of matter. However, science is based on the atom because it is the smallest distinct unit of matter.

Even though many super-tiny atomic particles exist, you only need to remember the three basic parts of an atom: electrons, protons, and neutrons. What are electrons, protons, and neutrons? Electrons are the smallest of the three particles that make up atoms. Electrons are found in shells or orbitals that surround the nucleus of an atom. Protons and neutrons are found in the nucleus. They group together in the center of the atom. That's all you have to remember. Three easy pieces!

There are almost 120 known elements in the periodic table. (117 as we write this) Chemists and physicists are trying to make new ones every day in their labs. The atoms of different elements have different numbers of electrons, protons, and neutrons. Every element is unique and has an atomic number. That number tells you the number of protons in every atom of the element. The atomic number is also called the proton number.

You can see that each part of the atom is labeled with a "+", "-", or a "0." Those symbols refer to the charge of the particle. Have you ever heard about getting a shock from a socket, static electricity, or lightning? Those are all related to electric charges. Charges are also found in tiny particles of matter.

The electron always has a "-", or negative, charge. The proton always has a "+", or positive, charge. If the charge of an entire atom is "0", or neutral, there are equal numbers of positive and negative charges. Neutral atoms have equal numbers of electrons and protons. The third particle is the neutron. It has a neutral charge, also known as a charge of zero.

Since the number of protons in an atom does not change, fewer or extra electrons can create a special atom called an ion. Cations have fewer electrons and have a positive charge. Anions have extra electrons that create a negative charge.

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Chem4Kids.com! This tutorial introduces atomic structure in chemistry. Other sections include matter, elements, the periodic table, reactions, and biochemistry.

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Chem4Kids

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What is matter? Matter is everything around you. Atoms and compounds are all made of very small parts of matter. Those atoms go on to build the things you see and touch every day. Matter is defined as anything that has mass and takes up space (it has volume).

What is mass? Mass is the amount of matter in an object. You might have a small object with a lot of mass such as a statue made of lead (Pb). You might have a large object with very little mass such as a balloon filled with helium (He). You should also know there is a difference between mass and weight. Mass is a measure of the matter in an object while weight is a measure of gravity's pull on an object.

What is volume? Volume is the amount of space something occupies. Words such as big, little, long, or short are used to describe volumes. A marble takes up a small volume while a star occupies a large volume. Different states of matter will fill volumes in different ways.

Even though matter can be found all over the Universe, you will only find it in a few forms (states) on Earth. We cover five states of matter on the site. Each of those states is sometimes called a phase. There are many other states of matter that exist in extreme environments. Scientists will probably discover more states of matter as we continue to explore the Universe.

What are the main states of matter? Everyone should know about solids, liquids, gases, and plasmas. Scientists have always known about solids, liquids, and gases. Plasma was a new idea when it was identified by William Crookes in 1879. We also like to talk about the Bose-Einstein condensate (BEC). It's a fun state of matter when you remove almost all energy from a system. The scientists (Cornell, Ketterle, and Wieman) who worked with the Bose-Einstein condensate received a Nobel Prize for their work in 2001.

What makes a state of matter? It's all about the physical state and energy in the atoms and molecules. Think about solids. Physical properties of a solid often include "hard" and "brittle." Liquids are fluidy, move around a little, and fill up containers. Gases are always around you, but the molecules of a gas are much farther apart than the molecules in a liquid. If a gas has an odor, you'll often be able to smell it before you can see it. The BEC is all about atoms that are closer and less energetic than atoms in a solid.

What is a physical change in matter? Molecules can move from one physical state to another ( phase change) and not change their atomic structure. Oxygen (O ₂) gas has the same chemical properties as liquid oxygen. The liquid state is colder and denser (less energy), but the molecules are the same. Water (H ₂O) is another example. A water molecule is made up of two hydrogen (H) atoms and one oxygen (O) atom. It has the same molecular structure whether it is a gas, liquid, or solid. Although its physical state may change because of different amounts of energy, its atomic structure remains the same.

So what is a chemical change in matter? Let's start with that glass of pure water. If the formula of water were to change, that would be a chemical change. If you could add a second oxygen atom to a water (H ₂O) molecule, you would have hydrogen peroxide (H ₂O ₂). The molecules would not be "water" anymore. In reality, there are a variety of steps that go into creating hydrogen peroxide from water.

Physical changes are related to changes in the immediate environment such as temperature, pressure, and other physical forces. Chemical changes occur when the bonds between atoms in a compound are created or destroyed. Generally, the basic chemical structure does not change when there is a physical change. Of course, in extreme environments such as the Sun, no molecule is safe from destruction.

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Chem4Kids.com: Matter: Definition and Overview

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Chem4Kids.com! This tutorial introduces basics of matter. Other sections include elements, the periodic table, reactions, and biochemistry.

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Cosmos4Kids

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Okay, this will be one of the few areas where we discuss pure ideas in astronomy. Eventually when you examine the universe, you have to say, "Ummm, excuse me. Where did this all come from?" We don't know. No one knows. There are only ideas and hypotheses. Mathematicians and philosophers have all discussed the idea. It's still one of those questions that aren't able to answer. We may never have and answer where all matter came from. However, we do have some evidence that the universe started with a big bang.

Scientists are currently working with the idea that the universe started with all of the mass in one big ball, billions of years ago. One day we suppose, that ball exploded. From that moment, time as we measure it began. The moment when this big ball exploded is called the big bang. The idea discussing the explosion is called the Big Bang Theory.

After the explosion, all of the dust and pieces began to spread out. As time passed, small pieces attracted other pieces and objects began to form. Eventually there were stars, systems, and galaxies. The important thing to remember is that this is an idea. We weren't there, we don't have pictures. The evidence we do have is indirect evidence. We look at the universe around us and our measurements have led us to this current conclusion. How did all the stuff get in a ball in the first place? Good question.

Encyclopedia.com (Big Bang Theory):
http://www.encyclopedia.com/topic/big-bang_theory.aspx
Wikipedia (Cosmogony):
http://en.wikipedia.org/wiki/Cosmogony
Wikipedia (Big Bang):
http://en.wikipedia.org/wiki/Big_Bang
Encyclopædia Britannica:
http://www.britannica.com/EBchecked/topic/40047/astronomy/314041/The-origin-of-the-universe
National Science Foundation:
http://www.nsf.gov/about/history/nsf0050 /astronomy/origins.htm
NASA/GSFC:
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970922g.html
NASA Video (The Universe is Born):
http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/The_Universe_Is_Born.html
Stephen Hawking:
http://www.hawking.org.uk/the-origin-of-the-universe.html

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Okay, this will be one of the few areas where we discuss pure ideas in astronomy. Eventually when you examine the universe, you have to say, "Ummm, excuse me. Where did this all come from?" We don't know. No one knows. There are only ideas and hypotheses.

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What's My Property: Crash Course Kids #35.2

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Electromagnetism - Magnetic Force: The Four Fundamental Forces of Physics #4b

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In this final segment on the four fundamental forces of physics, Hank tackles the magnetic force, the second of the two ways in which electromagnetism is apparent in the universe. Like SciShow on Facebook: http://www.facebook.com/scishow Follow SciShow on Twitter: http://www.twitter.com.scishow References: http://www.magnet.fsu.edu/mediacenter/publications/flux/vol2issue2/milestones.html http://theory.uwinnipeg.ca/mod_tech/node83.html http://www.magnet.fsu.edu/ http://www.explainthatstuff.com/magnetism.html Forces of Nature by P.C.W.

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Copyright © 2017 Discovery Education. All rights reserved. Discovery Education is a subsidiary of Discovery Communications, LLC.

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Copyright © 2017 Discovery Education. All rights reserved. Discovery Education is a subsidiary of Discovery Communications, LLC.

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Copyright © 2017 Discovery Education. All rights reserved. Discovery Education is a subsidiary of Discovery Communications, LLC.

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http://socratic.org/chemistry

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Bozeman Science

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Diagram

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Minute Physics

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Kurzgesagt

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Why Earth Is A Prison and How To Escape It

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PHET Simulation

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Move the sun, earth, moon and space station to see how it affects their gravitational forces and orbital paths. Visualize the sizes and distances between different heavenly bodies, and turn off gravity to see what would happen without it!

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Chem4Kids

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Chem4Kids.com: Elements & Periodic Table

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Chem4Kids.com! This tutorial introduces basics of elements and their organization. Other sections include matter, elements, reactions, and biochemistry.

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Physics4Kids

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There was this fellow in England named Sir Isaac Newton. A little bit stuffy, bad hair, but quite an intelligent guy. He worked on developing calculus and physics at the same time. During his work, he came up with the three basic ideas that are applied to the physics of most motion (NOT modern physics). The ideas have been tested and verified so many times over the years, that scientists now call them Newton's Three Laws of Motion.

The first law says that an object at rest tends to stay at rest, and an object in motion tends to stay in motion, with the same direction and speed. Motion (or lack of motion) cannot change without an unbalanced force acting. If nothing is happening to you, and nothing does happen, you will never go anywhere. If you're going in a specific direction, unless something happens to you, you will always go in that direction. Forever.

You can see good examples of this idea when you see video footage of astronauts. Have you ever noticed that their tools float? They can just place them in space and they stay in one place. There is no interfering force to cause this situation to change. The same is true when they throw objects for the camera. Those objects move in a straight line. If they threw something when doing a spacewalk, that object would continue moving in the same direction and with the same speed unless interfered with; for example, if a planet's gravity pulled on it (Note: This is a really really simple way of descibing a big idea. You will learn all the real details - and math - when you start taking more advanced classes in physics.).

The second law says that the acceleration of an object produced by a net (total) applied force is directly related to the magnitude of the force, the same direction as the force, and inversely related to the mass of the object (inverse is a value that is one over another number... the inverse of 2 is 1/2). The second law shows that if you exert the same force on two objects of different mass, you will get different accelerations (changes in motion). The effect (acceleration) on the smaller mass will be greater (more noticeable). The effect of a 10 newton force on a baseball would be much greater than that same force acting on a truck. The difference in effect (acceleration) is entirely due to the difference in their masses.

The third law says that for every action (force) there is an equal and opposite reaction (force). Forces are found in pairs. Think about the time you sit in a chair. Your body exerts a force downward and that chair needs to exert an equal force upward or the chair will collapse. It's an issue of symmetry. Acting forces encounter other forces in the opposite direction. There's also the example of shooting a cannonball. When the cannonball is fired through the air (by the explosion), the cannon is pushed backward. The force pushing the ball out was equal to the force pushing the cannon back, but the effect on the cannon is less noticeable because it has a much larger mass. That example is similar to the kick when a gun fires a bullet forward.

Or search the sites for a specific topic.

Newton's Laws Aboard The ISS (NASA-eClips Video)

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Physics4Kids.com: Motion: Laws of Motion

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There was this fellow in England named Sir Isaac Newton. A little bit stuffy, bad hair, but quite an intelligent guy. He worked on developing calculus and physics at the same time. During his work, he came up with the three basic ideas that are applied to the physics of most motion (NOT modern physics).

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Potential and Kinetic Energy

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Learn about conservation of energy with a skater gal! Explore different tracks and view the kinetic energy, potential energy and friction as she moves. Build your own tracks, ramps, and jumps for the skater.

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1. Inertia

2. Mass

3. Speed

6. Gravity

9. Kinetic Energy

10. Potential Energy

16. Molecules in Solids

17. Molecules in Liquids

18. Evaporation and Condensation

19. Expansion and Contraction

21. Temperature vs Heat

22. Atoms

23. Electrons

24. Conduction

27. Convection

28. Heat as Energy

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Khan Academy

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The periodic table - classification of elements

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Common terms describing the ways elements are classified in the periodic table.

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Bill Nye

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BILL NYE THE SCIENCE GUY - PHASES OF MATTER

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Crash Course

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The science of static electricity - Anuradha Bhagwat

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PHET Simulation

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Heat, cool and compress atoms and molecules and watch as they change between solid, liquid and gas phases.

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Crash Course

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Chemical Changes: Crash Course Kids #19.2

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Kurzgesagt

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The Beginning of Everything -- The Big Bang

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How Stuff Works

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Advertisement ­It all started when we went shopping for a magnet for a demonstration on liquid body armor. We wanted to show that a magnetic field could cause certain liquids to behave as solids. Along with the petri dishes and iron filings we needed, the Steve Spangler Science catalog had a neodymium magnet it described as "super strong."

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Crash Course

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Electric Current: Crash Course Physics #28

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Veritasium

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Link to Video

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How the Universe work(Ep1-The Bigbang)-Vietsub

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I will keep uploading Ep 2,3,... if I get more view. Thanks for watching my video,please share this link and do not try to upload others one like this as well. Mong mọi người ủng hộ clip này để mình tiếp tục up Season 2,3,4,...

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Bill Nye the Science Guy S01E18 Electricity