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# Energy Physics

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You eat multiple meals a day, but have you ever wondered which type of energy is stored in that food? There are multiple types of energy stores, but which fall into the same type? For instance, it may be difficult to accept the fact that the energy type that is stored in the food you eat is the same as the energy stored in a battery which we call chemical energy, or that the energy type used in the atomic bomb is also used to generate electricity, which we call nuclear energy. Enough wondering, let's dive into the concept of energy and get all these questions answered!

The food you eat stores chemical energy just like batteries do.

## Energy definition

It makes our lives easier to be able to access energy so easily. However, we can't see it. What does it do for us, and what exactly is energy?

Energy is the capacity to do work or generate heat. Energy can be transferred between different stores using energy pathways.

An object works by moving against a force over a certain distance. The units for energy are Joules, and the symbol J was named after the well-known physicist James Joule.

However, you should not be confused by definition - energy is used everywhere. For example, when you burn wood, the stored chemical energy in the wood is converted into thermal energy in the form of heat to keep you warm. This is similar to us getting heat and light from the sun. However, in the latter case, the initial energy is called nuclear energy.

## Energy stores

An object's or a system's energy is stored in different energy stores, and energy can be transferred between different types of stores. Let's have a look at the energy stores that you need to know about:

• Kinetic energy is the energy of motion. Any moving object possesses kinetic energy, and this energy store can be transferred to other objects through collisions. Also, kinetic energy can be transformed into other energy. For instance, when an object is moving on a surface with friction, kinetic energy is converted into thermal energy in the form of heat, which is usually considered lost energy.

When energy is transformed from one form to another, a fraction of energy is dissipated into an unwanted and disordered form. This is called wasted energy.

• Gravitational potential energy is the energy an object possesses depending on its position in a gravitational field. For example, if you put a ball on a hill, it will have gravitational potential energy. If you roll the ball downwards, this energy will be released and transformed into kinetic energy.

• Elastic potential (strain) energy is the energy an object has when it is elastic and stretched (for example, a spring or a string). The elastic object will snap back to its original position when you stop applying force on it. This is because the object has stored elastic potential energy.

Slingshots are an application of elastic potential (strain) energy.

• Thermal (internal) energy describes how hot an object is. Thermal energy is a type of kinetic energy as the heat of an object is determined by how fast its particles are moving around.

• Chemical energy is released (transferred to another energy store) when a chemical reaction occurs. The food you eat every day has stored chemical energy released after chemical reactions occur in your digestive system.

• Nuclear energy is the energy held up in the nucleus by strong forces. It can be released after nuclear reactions take place and used in nuclear power plants every day to provide electricity.

• Magnetic energy is stored in magnets, causing them to attract or repel each other.

• Electromagnetic energy is the energy that is being carried by electromagnetic waves. Of course, visible light is also an electromagnetic wave. It possesses this energy, but other examples can vary from radiowaves used in radios to carry information to X-rays used in medical physics.

For now, we will focus on two main types of energy, potential and kinetic.

## Kinetic energy

As you have learned before, kinetic energy is the energy an object possesses because of its movement. But what else does the kinetic energy of an object depend on? Let's look at the equation for finding kinetic energy to understand the concept better.

Where kinetic energyis measured in Joulesmass of the objectis measured in kilogramsand the speed of the objectis measured in metres per second.

As you can see, the kinetic energy of an object depends on both its mass and its speed. If you want to understand the concept of energy fully, you should also learn about potential energy.

## Potential energy

Unlike kinetic energy, potential energy has two main forms - gravitational and elastic.

### Gravitational potential energy

As you have learned, potential energy is the energy that an object possesses because of its position in a gravitational field. Now let's dive a little deeper and look at its equation to see what other factors affect the gravitational potential energy of an object.

Where gravitational potential energyis in Joulesmassis in kilogramsand gravitational field strengthis in newtons per kilogramand heightis in metres.

### Elastic potential energy

As you can see, gravitational potential energy depends on the position of the object in the gravitational field and its mass. Another form of potential energy is elastic potential energy which is the energy an object has when it is elastic and is stretched. Let's have a look at its equation to understand the concept better.

Where elastic potential energyis measured in Joulesspring constantis measured in newtons per metre, and the extensionis measured in metres.

The spring constant is a value that measures the stiffness of the spring and depends on the material used in the spring. This value is also equal to the force required to stretch the spring for one meter.

Now let's have a look at how energy is transferred and transformed between energy stores to understand how they are used in our everyday lives.

## Energy pathways

When energy is transferred between different stores, there are different ways in which energy transfer can occur. They are called energy pathways.

• Mechanically - a mechanical energy transfer occurs when work is done.

• By heating - when an object heats another object by transferring some of its thermal energy.

• Electrically - energy transferred by a charge moving through a circuit.

• By radiation - when an object radiates a wave which carries energy which can be passed onto another object.

A better understanding of how energy transfers between different stores can be gained is by considering what is happening to the object or what the object is doing.

Describe the energy transfers that occur when a person jumps into the air and falls back down again.

Solution

A person can jump into the air due to the chemical reactions in their muscles, causing the muscles to move, so there is initially a transfer from chemical to kinetic energy.

As the person moves higher up into the air, they begin to slow down due to the earth's gravitational field. Their energy is transferred from a kinetic energy store to a gravitational potential energy store. After reaching their maximum height, the person begins to accelerate back down towards the earth.

Their gravitational potential energy is converted back into kinetic energy. Or in other words, energy is transferred from a gravitational potential energy store to a kinetic energy store.

Energy transfer is important because you can't store energy in every useful form. For example, light is one of the most useful things in our lives, but it can't be stored. If you want to have light, you can carry a torch which has stored chemical energy in its battery. This chemical energy then causes an electric current which then causes the bulb to heat up. As a result of this heating process (which happens too quickly for the human eye to observe), the bulb emits light and allows us to see in the dark.

## Conservation of energy

The principle of conservation of energy states that energy cannot be created or destroyed. The amount of energy that existed back when the universe was formed is the same as the amount of energy that exists at the moment that you are reading this explanation. Energy can only be transferred between the different stores. For example, a battery doesn't just create energy from nothing. It contains chemical energy, which then is transferred into the circuit to create a current.

When energy transfers occur, not all energy is transferred into the desired store. Some of it is transferred to unwanted stores and is known as lost energy.

For example, when a bat hits a ball, there is a loud sound which means that some of the kinetic energy from the bat is transferred to sound waves. Another example is an object moving along a rough surface. It has to do work against friction, and some energy is lost since it transforms into thermal and sound energy.

But as you can see, even when we talk about lost energy, it isn't really lost but transformed into an unwanted disordered form of energy. So we can conclude that the initial total energy a system has is equal to the final total energy. We can mathematically express this conclusion as shown below.

## Efficiency

When you or a machine wastes energy while trying to do work, it is called inefficient. The " wasted " energy is what we previously called lost energy. In practice, you can't do work without lost energy, but you can reduce it to the desired minimum.

In physics, as the lost energy reduces, the efficiency becomes higher. Mathematically, it is the ratio of useful output energy to total energy input and can be expressed using the following equation.

In order to calculate efficiency as a percentage, we should multiply the result we get from the previous equation by a hundred.

Note that efficiency can't be equal to or higher than 100% in practice simply because there is always lost energy in some form which means that "useful energy output" is always going to be less than "total energy input"

A kettle hasof energy and convertsinto thermal energy. The rest of the energy is lost to the surroundings in the form of sound. Calculate the efficiency of the kettle.

Solution

Since the goal of the kettle is to provide thermal energy, the given value ofis the fraction of energy that we have named "useful energy output"

And it is said that the kettle is supplied withwhich is the fraction that we have named "total energy input."

We know that the formula for efficiency is:

If we put the given variables into the formula, we can find the kettle's efficiency.

fficiency labels can be found on almost every electrical device. Wikimedia Commons

## Energy Physics - Key takeaways

• Energy is the capacity to do work. It can exist in various forms and even be transferred between systems or bodies.
• Kinetic energy is the energy of motion. Any moving object possesses kinetic energy, and this energy store can be transferred to other objects through collisions.
• Gravitational potential energy is the energy an object possesses depending on its position in a gravitational field.
• Elastic potential (strain) energy is the energy an object has when it is elastic and is stretched (for example, a spring or a string).
• Energy is conserved. This means that it cannot be created or destroyed.
• An object's or a system's energy is stored in different energy stores, and energy can be transferred between different types of stores.
• In physics, as the lost energy reduces, the efficiency increases. Mathematically, it is the ratio of useful output energy to total energy input.

Energy is the capacity to do work. It can exist in various forms and even be transferred between systems or bodies.

According to the International System of Units (SI), energy is measured in Joules.

There are two types of potential energy. These can be defined as:

• Gravitational potential energy is the energy an object possesses depending on its position in a gravitational field.
• Elastic potential (strain) energy is the energy an object has when it is elastic and is stretched (for example, a spring or a string).

Chemical energy is the energy released (transferred to another energy store) when a chemical reaction occurs.

Electrical energy is the type of energy that results from the movement of charged particles.

## Final Energy Physics Quiz

Question

What is the principle of conservation of energy?

Energy can neither be created nor destroyed It can only be transferred from one form of energy to another

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Question

What are the different forms of energy?

• Electrical Potential Energy
• Nuclear Energy
• Mechanical Energy
• Light Energy
• Heat energy
• Gravitational Potential Energy.
• Chemical Potential Energy.

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Question

Which energy is released by chemical reactions?

Chemical Energy

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Question

What are some examples of mechanical energy?

Examples of mechanical energy are a moving car (kinetic energy), a hydrostatic turbine rotated by the flow of water, A bullet fired from a gun.

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What is chemical energy?

Chemical energy is a type of potential energy that is stored in the bonds between the atoms or molecules of different compounds. This energy is transferred when the bonds are broken during chemical reactions.

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Question

How is gravitational potential energy generated?

Gravitational potential energy is generated when an object is lifted to a certain height in the earth's gravitation field. it can also be defined as the work done to lift an object to a certain height h in the field.

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Question

What are the causes of heat energy?

Heat or thermal energy is produced due to the rapid motion of atoms. It can be said that this is due to the kinetic energy of the atoms, molecules, or ions. Heat transfer happens from a point of high temperature to low temperature due to conduction, convection and radiation.

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Question

What is light energy with examples?

Light energy is released when photons dissipate energy into the surroundings, this is what we see as visible light. Energy transfer occurs when the light comes in contact with an external surface.

Examples of light energy is photosynthesis in plants, light falling on solar panels. The sun is the largest source of light energy.

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Question

Which of the following types of energy is produced when an object is raised to a certain height?

Potential energy

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Which energy is stored in moving objects?

Kinetic energy

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Question

Heat energy is transferred from low temperature to high temperature

False

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Can light energy be stored?

False.

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Question

What is the largest source of energy in our solar system?

The sun is the largest source of energy in our solar system.

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Question

Which energy is released when the nucleus of an atom is split apart?

Nuclear energy

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Question

Which of the following is a mode of heat transfer?

All the options

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Question

What is meant by efficiency in physics?

Efficiency is the ratio of the useful energy of a system to the total input in that system.

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Question

The law of the conservation of energy states that...

energy is neither created nor destroyed, it is transferred into different forms or types.

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Is effectiveness a synonym for efficiency?

No, effectiveness is the degree of accomplishment of the desired result.

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Which of these is not a type of energy?

Thermal energy.

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Which units does efficiency have (standard unit)?

None.

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How does an energy loss happen during a process?

There is an energy loss during a process when a part of the energy input is transformed into other types of energy different from the useful energy output. For example, when an engine gets heated, this thermal energy is an energy loss.

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Question

How can we increase mechanical effiency when moving an object?

All of them are true.

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Question

If the electricity is transported over long distances, what happens when the current is reduced and the voltage for a given power is increased in power lines?

The electricity will travel faster and the energetic losses are reduced.

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Question

True or false: The wind contains kinetic energy.

True

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The first application of wind energy was sailing. Is this true or false?

True - this is the first known use of wind energy by humans.

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Windmills can be used for water pumping as one possible application of wind power. Is this true or false?

True

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How many major components does a windmill for grinding grain have?

This type of windmill has two major components:  The blades and the millstones.

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Question

In a wind energy system, the blades are used for:

Transforming the kinetic energy of the wind into mechanical power.

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Why are the blades are connected to the drive shaft in a wind power generator unit?

Once the blades rotates, the drive shaft will also rotate causing the electric generator to turn ON.

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What is the role of an electric generator in a wind power generator unit?

The electric generator will transform the mechanical power of the drive shaft into electrical energy.

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Question

How much did the worldwide wind power generation capacity increase year-over-year in 2020 compared to 2019?

53%

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Is wind a renewable source of energy?

Sunlight continues to shine and wind continues to blow despite the fact that their availability is dependent on time and weather conditions. Therefore, wind is a renewable source of energy.

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Question

One advantage of wind energy is that wind turbines are zero-emissions systems. Is this statement true?

While producing electricity using wind turbine units, we don't combust any type of fossil fuels. This result in zero emissions in the electricity generation process. However, if the production, transportation and maintenance of the turbine are taken into account, then they might not be truly said to be zero-emission energy sources.

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Question

Mention one disadvantage of wind energy power generation systems:

The high initial cost, threat to wildlife and the non-consistent availability of wind.

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Does the chosen site of wind turbines affect the wind power of the generation unit?

Wind turbines can only be installed where there is a somewhat steady wind of adequate strength.  If these conditions are not available, electricity cannot be reliably generated.

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How do wind power generation units affect the wildlife?

When birds, bats, and other flying critters are hit directly by a rotating wind turbine blade, they only have a small chance of surviving.

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The wind's kinetic energy is estimated to have transported Australian Aborigines from Southeast Asia's mainland to Australia 40 000 years ago. This is one example of the first applications of wind power.  Is this statement true or false?

True

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The topography and climate of Canada are estimated to have the ability to generate 485 GW from wind power. Is this statement true or false?

True

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Where does geothermal energy originate?

From the energy captured throughout the Earth's formation and from the radioactive decay of materials about 5 billion years ago.

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Why is geothermal energy considered a renewable energy resource?

Because its source is the nearly limitless quantity of heat generated by the Earth's core.

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Which geologic formations enable geothermal energy extraction?

Hydrothermal phenomena, geopressured, hot and dry rock, and magma.

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Question

Geothermal energy sources do not threaten the ozone layer. (True/False)

True

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Question

The carbon footprint of a geothermal power plant is high.

(True/False)

False

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Question

Geothermal energy sources may trigger earthquakes.

(True/False)

True

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Question

Geothermal energy sources do not emit greenhouse gases.

(True/False)

True

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Why is geothermal energy sustainable?

Because even if geothermal areas rely on a hot water reservoir, the volume extracted can be reinjected.

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What are some of the uses of geothermal energy?

Greenhouse and district heating, industrial use, thawing ice and snow, and thermal tourism.

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Question

A large area is needed for installing drilling machines. (True/False)

True

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Preparation and research costs are low. (True/False)

False

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Fossil fuels are needed for electricity generation with geothermal energy sources. (True/False)

False

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