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. 

Introduction to Physics

Energy

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!3

Laws of Motion

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. 

Laws of Motion 

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 seems 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.
• Forces are measured in Newtons. This is after Isaac Newton, not fig newtons, even if they are tasty.
• 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.

Learn English Conversation Unit 21 At the Restaurant

Learn English Conversation Unit 21 At the Restaurant

Friction

Friction

What is friction? 

Friction is the resistance of motion when one object rubs against another. Anytime two objects rub against each other, they cause friction. Friction works against the motion and acts in the opposite direction. 

Friction and Energy 

When one object is sliding on another it starts to slow down due to friction. This means it loses energy. However, the energy doesn't disappear. It changes from moving energy (also call kinetic energy) to heat energy. This is why we rub our hands together when it's cold. By rubbing them together we generate friction and, therefore, heat. 

The force F of friction pushes back on the block.

Preventing Friction 

In some cases we want to prevent friction so it's easier to move. A good example of this is a ball or wheel. They roll to help reduce friction. Another way to reduce friction is with a lubricant like grease or oil. Machines and engines use grease and oil to reduce friction and wear so they can last longer. 

Another way to reduce friction is to change the types of materials in contact with one another. For example, ice contacting with steel would produce less friction than rubber would on concrete. This is why ice skates slide so easily on the ice, but you don't slip when wearing rubber shoes on the sidewalk. These different materials are said to have different "coefficients of friction". 

Using Friction 

Friction is also a great help to us. After all, we would all just be sliding around everywhere if there wasn't friction to keep us steady. Friction is used in car brakes, when we walk or climb a hill, making a fire, skiing down a hill, and more. 

Experiment with Friction 

Different types of surfaces create different amounts of friction. Some materials are much smoother than others. Take three flat objects with different types of surfaces. Set them on one end of a tray and slowly lift it. The item with the least friction will start to slide first. 

There are two main factors that will influence the total amount of friction: 1) the roughness of the surfaces (or the "coefficient of friction") and 2) the force between the two objects. In this example, the weight of the object combined with the angle of the tray will change the force between the two objects. Play around with different objects and see how these two factors change the friction. 

Types of friction

• Dry Friction - This is what we've been mostly talking about here. Dry friction occurs when two solid objects touch each other. If they are not moving, it is called static friction. If they are moving, it is called kinetic or sliding friction.
• Fluid Friction - Fluid friction involves a fluid or air. The air resistance on an airplane or water resistance on a boat is fluid friction.
• Rolling Friction - Rolling friction occurs when a round surface rolls over a surface, like a ball or wheel.

Fun facts about Friction

• Although wheels are great for rolling and reducing friction, they couldn't work without friction.
• It would be really tough just to stand up without friction.
• Friction can generate static electricity.
• The harder two surfaces are pressed together, the more force it takes to overcome the friction and get them to slide.
• Fluid friction is used a lot in water parks so we can slide smoothly and fast down giant slides.

Черные дыры - от рождения до смерти