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What does one mean when they say they feel energetic today? Is it the same energy that powers cars, buses, planes, and other modes of transportation? If not, can we convert one type of energy to another? To answer these questions, it is essential to understand the different forms of energy present in our universe. Some energies are abundant such as light energy, whereas others are limited due to resources. This article goes through the definition of energy, different forms of energy, and how it can be transferred from one form to another?
Energy is what moves the world around us. It is always transferred whenever a physical action (even at atomic levels) takes place, or the state of a system is changed. A system is defined as an object or a group of objects with a defined boundary. Systems can be of 3 types:
There are 3 types of thermodynamic systems, the first tube is an open system, the second tube with a closed mouth is called a closed system and finally, the system that is completely separated from the system is called an isolated system, Mayyskiyysegreyy CC-BY-SA4.0
We must apply an external force to accelerate an object. As a consequence work must be done, which can mean only one thing. Energy needs to be transferred when the object moves at a new constant speed. The energy transferred is known as kinetic energy.
Kinetic energy is a form of energy that an object has due to its motion.
When an external force causes an object to move, work is done i.e. energy is transferred. This is the kinetic energy
of the object. It is measured in
or
. Kinetic energy
depends on two factors. The mass of the object and the velocity at which it's moving
Examples of Kinetic energy in everyday life, kinetic energy is perhaps the most often observed form of energy and the most intuitive to humans, StudySmarter Originals
It can also be defined as the work done on an object of mass
to accelerate it to a speed
. The same amount of work will be done to bring this moving body to a stop. however, the work done will be negative because it is against the motion of the object.
or in words
The kinetic energy of a moving body depends on two factors, its velocity, and mass.
or in words
Kinetic energy can be present in different forms, such as translational and rotational kinetic energy. We will look into mechanical and heat energy in detail as they're important. Later we will also discuss the other forms of kinetic energy.
One of the fundamental laws of the universe is that energy can neither be created nor destroyed; it can only be transferred from one form to another. This principle is known as the conservation of energy. What this says is the total energy inside a system is always constant. So then, what are these different forms that we've been talking about so far?
When a fossil fuel undergoes combustion, it converts the chemical energy stored in the fuel into thermal energy. If you consider such an isolated system, the amount of energy is always constant; it just changes from one form to another.
So then what is mechanical energy?
Mechanical energy is the energy possessed by an object due to its motion, such as a speeding car, falling leaf, etc, or by virtue of its position.
It is given by the following equation:
or in words
Potential energy is also known as stored energy. When someone says that they have the potential to do great things, they're talking about something innate or hidden within the subject. The same logic applies when describing potential energy. Potential energy can be broken down based on the system and the forces acting on it. we'll look into potential energy in detail in the later sections. But take a look at the example below to understand how the mechanical energy of an object remains constant?
The mechanical energy of a vehicle on a hill, over the journey of the object the mechanical energy will remain constant, dummies
When the object climbs the hill its potential energy is constantly increasing, but as its speed is decreasing the kinetic energy keeps on reducing. at the top of the hill, the potential energy is maximum and the kinetic energy is Zero. When the object travels downhill, its potential energy starts decreasing and the kinetic energy keeps increasing. As shown in the figure the sum of both energies will always be constant, which again follows the principle of conservation. Throughout the journey, the energy is transferred from one form to another.
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. There are 3 ways of transferring heat between two bodies. Conduction, convection and radiation.
Conduction is when heat energy is transferred between neighbouring atoms or molecules due to collisions between them.
Convection is the upward movement of molecules and atoms with a higher temperature causing the denser and cooler molecules to sink inevitably causing heat transfer.
Radiation is a process in which heat waves are emitted and may be absorbed, reflected, or transmitted through a colder substance leading to the transfer of heat.
Let's understand this using an example,
When Heating a pot of water, heat transfer takes place using the three methods heat transfer through conduction occurs when the metal handle is heated as heat transfers through the metal pan. Next. Radiation occurs as the infrared waves heat the bottom of the pan. And finally, heat transfer due to convection occurs when the water molecules at the bottom rise and transfer heat.
The change in thermal energy can be given by the following equation:
or in words
The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
We already know that kinetic energy can be stored in different ways and is measured in
. These forms of kinetic energy are nothing but the different ways kinetic energy is transferred throughout the universe.
We now have a clear idea of kinetic energy and its many forms. Now, let's look at another type of energy that is mostly stored in objects and when released can be converted into kinetic energy.
Why does a rock dropped from a great height into a pool produce a much bigger splash than one dropped from just above the water surface? What has changed when the same rock is dropped from a greater height? When an object is elevated in a gravitational field, it gains gravitational potential energy (GPE). The elevated rock is at a higher energy state than the same rock at surface level, as more work is done to raise it to a greater height. It is called potential energy because this is a stored form of energy that when released is converted into kinetic energy as the rock falls.
Gravitational potential energy is the energy gained when an object is raised by a certain height against an external gravitational field.
The gravitational potential energy of an object depends on the height of the object, the strength of the gravitational field it is in, and the mass of the object.
The water is stored at a height as stored potential energy. When the dam opens it releases this energy and the energy is converted into kinetic energy to drive the generators, Lijovklm CC-BY-SA-4.0
Water stored on top of a dam has the potential to drive hydroelectric turbines. This is because gravity is always acting on the body of water trying to bring it down. As the water flows from a height its gravitational potential energy is converted into kinetic energy. This then drives the turbines to produce electricity (electrical energy). All types of potential energy are stores of energy, which in this case is released by the opening of the dam allowing it to be converted into another form.
The gravitational potential energy gained by an object of mass
when it is lifted to a height
in a gravitational field of
is given by the equation:
or in words
where
is the gravitational potential energy in
,
is the mass of the object in
,
is the height in
, and
is the gravitational field strength on Earth
. But what about the work done to raise an object to a height? We already know that the increase in potential energy is equal to the work done on an object, due to the principle of conservation of energy:
or in words
Because potential energy is a stored form of energy, it can be stored in different forms. Potential energy can also be stored in the bonds of chemicals or a stretched object. Let's look at these in detail.
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. Common examples of chemical energy are:
Nuclear potential energy is the energy that is within the nucleus of an atom. It is one of the most powerful sources of energy in the universe. Nuclear energy can be released by
The energy stored in elastic materials as a result of stretching or compressing is known as elastic potential energy.
It is given by the following equation
or in words
where
is the constant of elasticity of the material and x is the distance to which it is stretched. It can also be defined as the work done to stretch a rubber band of elasticity
by extension
.
The spring in this figure is stretched by a force that causes it to extend. If we know the distance over which it extends and its spring constant, we can find the elastic potential energy that is stored in it, StudySmarter Originals
In the figure above a spring with spring constant
is stretched by a force
over a distance
. The spring holds elastic potential energy. Once released this potential energy moves the rubber band to its original position. It can also be defined as the work done to stretch the spring over a certain distance. The energy released will be equal to the work that was required to stretch the spring.
Whenever the state of a system changes energy is being transferred from one state to another, energy can be transferred by the following types of energy transfers. Let's see how energy is transferred in the world around us
We also know another way of saying work is done is by saying that energy was transferred from one form to another. Let's work on a few examples that will test your understanding of the concepts we covered in this article.
Calculate the braking force required to stop a vehicle of mass
moving at a speed of
in
.
We know that work done to stop a moving vehicle is equal to the kinetic energy of the moving vehicle. Using this we can equate both the terms of work done and kinetic energy. From there we can calculate the force that will be required to stop this vehicle.
So the force required to stop this vehicle is
. Let's simplify this problem and try to understand how energy is being transferred from one form to another.
The brakes clamp down on the moving wheel, the brake showed is a high friction material that converts the kinetic energy of the wheel into heat, and in this process, the bike slows down, Wikimedia Commons
When we push or pull an object mechanical energy is transferred. In this case, the mechanical energy is being transferred. let us look at the case of a speeding bike. The bike has kinetic energy due to its mass and the velocity at which it is moving. Now let's imagine, that the rider presses the brake lever. Here the friction from the brakes converts the kinetic energy of the moving vehicle into heat. This is an example of how energy transfer converts the kinetic energy of a moving vehicle and stops it. in the above image, you can see how the brake lever pushes the brake shoes onto the wheels which ultimately slows it down.
What about the energy conversions when an object is falling? let's find that out using our next example.
If a
apple is dropped from a height of
above the ground, at what speed will it hit the ground? Ignore any effects of air resistance.
The speed of a falling apple increases as it is accelerated by gravity, and is at a maximum at the point of impact, StudySmarter Originals
The gravitational potential energy of the object is converted into kinetic energy as it falls and increases in velocity. Therefore the potential energy at the top is equal to the kinetic energy at the bottom at the time of impact. using the equation for mechanical energy.
The total mechanical energy of the apple at all times is given by:
When the apple is at a height of
, the velocity is zero hence
. Then the total energy is:
When the apple is about to hit the ground the potential energy is zero, hence the total energy is now:
Velocity during impact can be found by equating the
to
. At the moment of impact, the kinetic energy of the object will be equal to the potential energy of the apple when it was dropped.
The apple has a velocity of
when it hits the ground. The potential energy of the apple is converted into kinetic energy as it falls.
Light energy is released when photons carry 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. An example of light energy is photosynthesis in plants, light falling on solar panels. The sun is the largest source of light 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 high to low temperatures due to conduction, convection and radiation.
Gravitational 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
Chemical energy is a type of potential energy stored in the bonds between the atoms or molecules of different compounds. This energy is transferred when the bonds are broken during chemical reactions.
Examples of mechanical energy are a moving car (kinetic energy), a hydrostatic turbine rotated by the flow of water, and A bullet fired from a gun.
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