Kinetic Energy Defined (What You Need To Know!)

# Kinetic Energy Defined (What You Need To Know!)

Most of us are familiar with the term kinetic energy. However, if you don’t have a solid understanding, you’re not alone. As the world around us shifts to a more sustainable living mindset, we may find ourselves asking, “What is kinetic energy? Can we harness it to create clean energy”?

This article will cover everything you need to know about kinetic energy. From its definition and characteristics to examples and how we use it in chemistry, and you’ll find kinetic energy explained in both technical and simplified terms. Read on to gain a basic understanding of this fascinating form of energy.

## What Is Kinetic, and What Does It Mean?

For starters, you’ll need to know what kinetic means. The Merriam-Webster Dictionary defines the word kinetic as “of or relating to the motion of material bodies and the forces and energy associated therewith.”

That sounds a bit complex, so let’s sum it up. The term kinetic originates from the Greek word kinesis and means motion. Therefore, kinetic energy is the energy of motion

## Kinetic Energy Explained in Simple Terms

There are only two primary forms of energy. Kinetic energy (KE) is one of them. Further explained, it’s the Any object (also known as mass) that is moving is said to have KE.

For something to have KE, something must do work to it. In this case, work is considered a force acting on an object the same direction as the motion. The amount of work required depends on the object’s mass and the distance we’d like the item to travel.

For example, think about pushing your child down a sledding hill. Here, the work is you pushing your child who is now sledding down the hill. This relationship between work and kinetic energy is called the work-energy theorem This theorem is related to Newton’s second law, which states that “the acceleration of an object is directly related to the net force and universally related to its mass.” Therefore, accelerating an object, meaning an increase in KE, is directly related to two things: force (which gives it speed) and mass.

Simply put, the more mass and velocity an object has, the more kinetic energy it will have.

At this point, you’re probably asking, aren’t there two forms of energy? Yes, there are. The second is called potential energy.

To easily remember this, think of kinetic and potential energy as opposites. While kinetic energy is the energy of motion, potential energy is stored energy, meaning it has the potential for motion but is currently at rest.

A great example of kinetic and potential energy is a bow and arrow. When drawn back, the bow has potential energy. When released, the potential energy transfers to the arrow, giving it kinetic energy. Today, we’ll keep our focus on the energy of motion.

## What Are Five Kinetic Energy Examples?

To further answer the question, “What is kinetic energy?” let’s take a look at some basic examples of objects with KE before we continue.

1. A roller coaster car in descent
2. An airplane in flight
3. A flowing river
4. Riding a bike
5. Wind

These examples of objects with KE should give you a visual reference to simplify the concept. An airplane in flight has a fast velocity and a large mass which gives it a lot of KE. In contrast, a flying insect has a relatively small amount of KE due to its slower velocity and smaller mass.

Fun fact: in billiards, when a cue ball collides with a stationary ball, it comes to a complete stop, transferring its full momentum and complete KE. This is called an elastic collision. An inelastic collision would be when the total momentum is conserved, but there is a KE transformation.

## What Are the Characteristics of Kinetic Energy?

The movement of an object, sometimes referred to as a body, produces kinetic energy. It enables us to generate changes related to speed. Here are a few more main characteristics of kinetic energy:

Fun fact: Lord Kelvin received credit for first using the term kinetic energy around the year 1849, but KE conceptually dates back to the days of Aristotle.

### An Object Will Maintain the Same Amount of Kinetic Energy Until It Slows Down or Speeds Up.

Kinetic energy increases with speed. For example, a car driving down the road has KE. When set on cruise control, the car’s KE will remain the same. When the vehicle speeds up, there is an increase in the energy of a body, aka the kinetic energy increases.

### Kinetic Energy of an Object Is Greater When the Object Has a Greater Mass.

For example, if a car and a truck are driving at the same speed, the truck will have total kinetic energy because it has more mass than the car.

## What Are the Factors That Affect Kinetic Energy?

The answer lies in what we read above: mass and speed. When the mass of an object doubles, its kinetic energy doubles. However, when the speed of an object doubles, its kinetic energy quadruples.

On the contrary, when a moving object collides with another object, its KE is transferred. This makes the rule for kinetic energy: = 1/2 m v2, where m is the mass of an object and v is the velocity or speed that object carries.

Any time you know the mass and the speed of a moving object, you can find out how much kinetic energy it has. We will revisit this later for a more thorough explanation.

## Can Kinetic Energy Transform Into Alternative Forms of Energy?

Yes, kinetic energy can transform into alternative forms of energy, such as heat. Heat energy is also known as thermal energy. When the atoms and molecules of a substance vibrate faster due to a temperature rise, we get thermal energy. More to come a bit later on alternative forms of energy as well.

Fun fact: Boiling a tea kettle of water is an excellent example of both kinetic and thermal energy.

## What Are the Types of Kinetic Energy?

We know that kinetic and potential energy are the three main types of energy. When we take it one step further, we learn that there three main types of kinetic energy:

1. Translational
2. Rotational
3. Vibrational kinetic energy

### Translational Kinetic Energy Is Dependent on Motion Through Space

An example of this is a ball that is free-falling from a rooftop. As the ball continues to fall straight down, it has translational kinetic energy.

Kinetic energy is directly proportional to the mass of the object (m) and the square of its speed (v). So, the rule for the translational kinetic energy of a body, as mentioned above, is one-half the product of the object’s mass (1/2 m) and the square of its velocity (v2).

Neatly written, kinetic energy equation, given by Newtonian (classical) mechanics is:

KE = 1/2mv2

However, this equation no longer valid when it comes to objects that are traveling at the speed of light. Why? Because when you’re dealing with extremely high-speed particles, the values become too small. Here, we must use the laws of relativity. Relativistic kinetic energy is the increase in mass over what it has at rest, multiplied by the square of the speed of light.

### Rotational Kinetic Energy Is Dependent on Motion Centered on an Axis

We’ll use that same ball from earlier as an example, but this time, the ball rolls down a ramp rather than free-falling. Now, it has rotational kinetic energy.

With a rotating object the KE will depend on the object’s angular velocity in radians per second and the object’s moment of inertia. Angular velocity is the rotational speed. The moment of inertia is how easy it is to change the object’s rotation.

• Moment of inertia (I) corresponds to mass.
• Angular velocity (ω) corresponds to translational velocity.
• Rotational kinetic energy is equivalent to one-half the product of the moment of inertia (I = kg∙m2) and the square of the angular velocity (ω = radians/s).

## What Is the Conservation of Kinetic Energy in Physics?

The law of conservation of energy states that energy can neither be created nor destroyed; it merely changes form. Now, we know that some external forces, such as friction and gravity, will slow an object down over time, seeming to take away its energy. However, this energy believed to be lost is actually reappearing in another form and is, in fact, always conserved.

When friction slows down an object, KE converts into heat or thermal energy. In this general form, conservation of energy relates to thermodynamics’ first law, where energy transfers from one place to another and one state to another.

Fun fact: Thermodynamics was born when scientists worked on building and operating steam engines back in the 19th century.

## What Are the Forms of Kinetic Energy?

We know the types of KE and how we use it in science. Let’s make it more relatable now by discussing the five different forms of KE and how we use it in our everyday lives, especially at home. The acronym is MELTS:

### 1. Mechanical Energy

Mechanical energy is the energy that we can see. The faster an object moves and the more mass it has, the more mechanical energy it has and the greater ability it has to do work. One example is when a bowling ball strikes a pin. But more impactful, a windmill can harness wind energy, and a hydroelectric dam can generate electricity from a flowing water source.

### 2. Electrical Energy

Electrical energy is better known as electricity.  We get electricity when negatively-charged electrons flow around a circuit. The movement of these electrons powers our everyday devices, such as a desk lamp or a cell phone that’s plugged into the wall.

### 3. Light Energy (or Radiant Energy)

Light energy, a form of electromagnetic radiation, refers to the energy that travels by particles or waves. It’s the only form of energy that’s visible by the human eye. An obvious example of radiant energy is the heat we get from the sun. Other examples are lightbulbs, the toaster in your kitchen, and X-rays.

### 4. Thermal Energy

Like radiant energy, we can experience thermal energy in the form of heat (yes, heat is a measure of KE!). However, thermal energy has to do with the atom and molecule activity level in an object. The quicker they move, the more they collide with each other.

Some great examples of thermal energy are cooking in your oven or running the engine of your car. Another example has thermal energy right in its name: Geothermal energy is a renewable resource that we use to generate electricity for our homes.

### 5. Sound Energy

Sound energy generates through vibrations. An object creates waves of movement through a medium, such as water or air. Once it reaches our eardrums, they vibrate, which cues our brain to interpret the vibration as sound. Everything from the loudest of drums to the tiniest buzzing bee creates vibrations, which, in turn, causes sound.

## What Are Methods To Harness Kinetic Energy? What Problems Do We Face?

Kinetic energy harvesting, or scavenging, accumulates and stores wasted energy to convert it into electrical energy. Later this energy is used to power small electronics.

Sources include renewable energy sources such as the sun, wind, water, and geothermal heat. However, we also use artificial sources generated by humans, such as walking, vehicle motion, and system vibration.

Harvesting KE from these sources has proven to be a challenge. Physical structures are necessary to capture the energy. An electromechanical transducer is also needed to convert the energy into electricity. It has been challenging to find suitable materials that suit the needs of both large-scale and smaller-scale applications.

The overhead cost needs to remain low, and the devices used need to be energy efficient. Often, the devices are required to be lightweight and portable as well. Experts believe that the answer to improved KE conversion lies in finding new materials.

We’re off to a good start with low-cost photovoltaic materials that exploit solar energy and newly improved low-cost composite turbine blades to harness the wind.

## What Is Kinetic Energy? Now You Know!

With kinetic energy explained, you now know that the energy of motion is a regular part of our everyday lives. From thermal energy to electrical energy, we rely on kinetic energy for everything, including leading a sustainable lifestyle.

When you choose green energy options, the positive impact you make on the world around you is something that you can feel good about forever. Plus, you’ll find the potential savings aren’t so bad either.

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