Kinetic Energy Definition | Learning Resource

Kinetic Energy Explained and Definition | A Learning Resource

by | Educational, Energy

The Oxford Learner’s Dictionary defines kinetic energy as “of or produced by movement.” In this guide, we’ll break down this natural force so you can have kinetic energy explained in clear terms.  

We‘ll look at how kinetic energy interacts with other forms of energy in an accessible and formative manner. We’ll also break down how it affects our daily lives and how it defines the world as we see it. 

Kinetic is the energy of motion or the amount of energy an object has as it moves around a system. Kinetic energy is determined by the mass of an object and its velocity or speed, and it can be transferred from one object to another, such as during collisions.  

A two-ton parked car has potential energy because it’s not moving. To make any object move, we need to apply force. Applying force requires us to do work on the object. As we work on the object, there is a transfer of energy, and the object moves — this is kinetic energy. 

Let’s start moving our car with its 4,409-pound mass (m) and apply force to it so that it reaches a speed of 50 miles per hour (velocity, or v). The force — i.e., the energy transferred to it, or the amount of work — is known as kinetic energy (KE). 

The kinetic energy equation for total kinetic energy is: KE = ½ mv2 

Speed and mass affect the amount of kinetic energy an object has. We can work out how much kinetic energy an object has, which is measured in Joules, by using this kinetic energy calculator. 

Using our car example, and a bike, here are some workings for kinetic energy (KE):  

  • Our 4,409-pound car traveling at 50 miles per hour has a KE reading of 499,584 Joules. 
  • If our car travels at 10 miles per hour, it has a KE reading of 19,983 Joules. 
  • An 18-pound bike traveling at 50 miles per hour has a KE reading of 2,040 Joules. 
  • Objects that are moving have kinetic energy that can be measured by their speed and mass. As you can see in the workings above, an object’s kinetic energy stays constant until its speed or mass changes.

As mentioned, kinetic energy can be transferred from one object to another. If a football hits the windshield of our car going 50 miles per hour, some of the car’s energy (499,584 Joules) will move to the football and cause it to bounce away. At 10 miles per hour, the football would not bounce very far away because the car has less kinetic energy (19,983 Joules) to transfer. 

Newton’s second law says that force is mass times acceleration — the more mass an object has, the more force you need to move it. Suppose we load our bike with heavy panniers full of cement. It will take more force — in this case, using mechanical energy to pedal — to make a cement-laden bike travel at 10 mph than the same bike with no panniers of cement. 

What Is Kinetic Energy the Energy Of? 

Kinetic energy is the energy of motion, and potential energy the second main form of energy. There’s a strong relationship between kinetic and potential energy. 

Energy cannot be destroyed, according to the law of the conservation of energy; it can only be transformed from one form of energy into another. 

A yo-yo or a pendulum is a great way to demonstrate the relationship between kinetic and potential energy. A yo-yo that’s resting in your hand has potential energy stored in it. Once you drop the yo-yo, that stored energy is converted into kinetic energy because it’s moving. When you catch the yo-yo again and hold it, the kinetic energy converts back into potential energy. A pendulum swinging uses the same principle. 

What Are the Characteristics of KE? 

Kinetic Energy Characteristics | Image of a pool ball producing energysource

Kinetic comes from the Greek word “kinesis,” meaning motion. Kinetic Energy can be seen in many forms, from wind to electricity, and includes movements like vibration and rotations. It can be moved in any direction. 

As we’ve seen, kinetic energy increases when mass and/or speed increases, and KE remains the same unless an object speeds up or slows down. There are two main types of kinetic energy: translational kinetic energy and rotational kinetic energy. 

The translational kinetic energy of an object is work required to take it from a resting position to a desired velocity. (For example, moving our parked car up to 50 mph.) Translational, in this sense, is about moving our object from one point to another along a linear path. A stationary cue ball in billiards, after being struck by a player’s cue and moving down the table, has translational kinetic energy. 

Rotational kinetic energy depends on motion centered on an axis. If you play billiards well enough, or poorly enough, the cue ball you strike will hit another billiard ball, and both balls move. Some of the cue ball’s kinetic energy is turned into sound energy as the balls clack together. Some energy is lost as heat energy. Some of the cue ball’s kinetic energy is transferred to the second billiard ball. There is also some energy transferred as rotational kinetic energy. Following their collision, the billiard balls spin on their axis, which is called angular velocity, and move away from each other. 

The balls also go through a moment of inertia, a measurement of a body’s resistance to a change in its rotational motion. Both billiard balls require a certain quantity of energy to rotate. 

The Moon orbiting the Earth, and the Earth circling the sun are examples of rotational kinetic energy. Our bikes and cars convert the rotational kinetic energy of their wheels into translational kinetic energy, creating linear motion that makes the vehicle move. 

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What Is Kinetic Energy Measured In? 

The kinetic energy (E, Ek, or KE) of a moving object is measured in Joules (J). It varies according to its speed (v) and mass; m is for mass in the formula below. Mass and speed are scalar quantities because they can be described with numerical values only. 

Kinetic energy is proportional to mass (m) and proportional to the square of its velocity. The formula is: 

Kinetic energy: KE = ½ mv2 

What Are 5 Kinetic Energy Examples? 

There are five main types of kinetic energy: radiant, thermal, sound, electrical, and mechanical. 

Radiant energy concerns ultraviolet light and gamma rays that are continually moving around in the universe. Sound energy is kinetic energy in the form of vibrations and noise, such as someone banging drums. 

A roller coaster has more kinetic energy when it’s moving down its tracks. Once it starts to climb back up, going more slowly, it has less kinetic energy. As the roller coaster climbs up, it works against gravitational potential energy, which is the energy of position. The higher the roller coaster climbs, the more gravitational potential energy it acquires, and the faster it will go. It will have more kinetic energy when it descends, too. 

An airplane has little kinetic energy when waiting on the runway. Once flying, it has a lot of kinetic energy in the form of mechanical energy because of its massive body flying at great speed. 

Electrical energy comes from electrons moving to make electricity; it is this movement that makes electrical energy kinetic energy. When you switch on the lights, an electric current moves from the wall to the light bulb, creating light energy. Turning on a light does not mean electricity travels at the speed of light; it’s slower because the cable’s resistance slows the electricity down. 

Electric stoves work similarly. Once plugged into a power socket and turned on, the electricity moves into the heating coils and changes into thermal energy, causing the coils on the stove to heat up. This heat is then transferred to pots and pans so we can cook. 

A car battery is an excellent example of kinetic energy as chemical energy. A circuit is established with the battery, which starts a chemical reaction in the battery. The reaction makes electrons move in an electric current, bringing electrical energy to the car’s circuits. 

Is Heat Kinetic Energy? 

Heating Kinetic Energy | Thermal Example on Stovesource

Yes, heat is kinetic. Heat energy is another name for thermal energy. It’s kinetic because of the constant movement of the object’s atoms and molecules. Objects have a temperature, and they can transfer heat to another object via these moving atoms and molecules. 

Objects often undergo a reaction, such as passing electrical energy into our stoves, to change temperature. This higher temperature (on the stovetop) can then be given to a saucepan, thanks to the increased movement of atoms and molecules. 

Thermodynamics is different. Thermodynamics looks at the connection between thermal energy and work — for example, how a car engine turns heat into movement and mechanical energy. 

Is a Fan Kinetic Energy? 

Yes. A fan’s blades move, and the energy of motion is kinetic energy. The fan is plugged in, and electrical energy (kinetic) passes into its motor, converting the electrical energy into kinetic energy by turning the blades. 

What Are Examples of Kinetic Energy at Home? 

There are many examples of kinetic energy at home, from someone knocking on your door (sound energy) to someone turning on the light (electrical energy). When someone walks around the house, that’s the kinetic energy of a body. If you turn the tap on, the running water has kinetic energy, as does a basketball if you are shooting hoops in the yard. 

What Are Forms of Kinetic Energy? 

Let’s consider the five main types of kinetic energy: 

  • Radiant 
  • Thermal 
  • Sound 
  • Electrical 
  • Mechanical 

Radiant energy is all around us in the form of ultraviolet rays, even in your house. If you don’t want them there, well, there are external forces we cannot control. 

Thermal energy can be warm and cold. Suppose you put ice into a glass of water. In that case, the thermal water temperature is warmer than the ice, which then melts and reduces the water temperature. 

The fan we mentioned earlier will make a small, whirring sound; this is sound energy caused by vibration. It also uses electrical energy when switched on, and flicking that switch is mechanical energy. 

What Factors Affect Kinetic Energy? 

There are two factors that affect kinetic energy: mass and speed. An object maintains its kinetic energy if there’s no change to these two elements. Increase or decrease either mass or speed and an object’s kinetic energy changes. 

Kinetic energy grows at the square of the speed; this means that when the mass of an object doubles, so does its kinetic energy.  

When you double an object’s speed, this results in a quadrupling of its kinetic energy. Suppose you think about two identical cars, one traveling double the other’s velocity. In that case, it takes the faster car four times the distance to stop than the slower car, assuming equal braking forces. Flipping that around to acceleration, it takes four times the amount of work to double the faster car’s speed. 

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What Is Kinetic Energy in Chemistry? 

Kinetic energy is the same in chemistry as in physics — the energy an object possesses while it is in motion. 

Chemical energy is energy stored in atoms and bonds. Once a circuit is established, a car battery produces a chemical reaction that produces kinetic energy in the form of electricity. Burning wood provokes a chemical reaction that converts its chemical energy into thermal energy. 

Humans perform chemical reactions on the food we eat. Our stomachs break down its atoms and bonds to create mechanical energy to power our bodies. 

What Are Methods to Harness Kinetic Energy? 

Kinetic Energy | Harnessed in a Windmill - Energy being producedsource

Some of the most well-known methods of harnessing kinetic energy come in the renewable energy fields. 

Humans have used wind for centuries to power everything from windmills to sailboats. In the 21st century, our relationship with wind extends to the building of wind farms to provide electricity for our homes and businesses. The kinetic energy of the wind moves the blades of wind turbines, which rotate a generator that creates electricity. 

The kinetic movement of water turns similar generators at hydropower stations with steam doing the same at geothermal power stations. Another example includes using solar panels to capture the sun’s rays. The sun’s photons push electrons from atoms to create electricity. 

What’s the Problem With Trying to Harness Kinetic Energy? 

Moving objects are quite hard to stop, which makes it hard to harness their kinetic energy. Try to stop a moving car or a speeding plane, and the issues are apparent. 

Those we can harness, such as wind and solar, are not always reliable. Windy days are great for producing power but can be followed by calm ones when wind turbines won’t turn. Sunny summer days are perfect for solar power, but long, dark, and cloudy winter days not so much. What Is the Conservation of Kinetic Energy? 

Kinetic energy can be conserved in what are called collisions. There are two types to consider: inelastic collisions and elastic collisions. 

Let’s start with the most commonly seen type, which is an inelastic collision. An inelastic collision occurs when two objects collide, and some energy is lost. Momentum continues, but some kinetic energy disappears.  

Examples include bouncing a ball that doesn’t bounce up as high as its starting point. Or, take two cars hitting each other: some kinetic energy is lost as both vehicles slow down and stop. A perfectly inelastic collision occurs when all momentum is lost, such as slinging mud against a wall. 

An elastic collision sees all kinetic energy remain the same. Think about a parked car on a level road with no brakes applied. Now let’s say a heavier van hits the parked car. For argument’s sake, we’ll say the van had 60,000 Joules of kinetic energy at the point of impact.  

The car is moving after the crash, with, say, 45,000 Joules of kinetic energy. The van is moving more slowly now, with 15,000 Joules of kinetic energy; the original 60,000 Joules of kinetic energy stays the same. An elastic collision is when the total kinetic energy of two bodies remains the same after colliding. 

What Is the Rule for Kinetic Energy? 

Kinetic energy is the energy an object bears due to its motion — it’s the amount of work required to accelerate an object from a resting position to a stated velocity. 

What’s Next for Kinetic Energy? 

We can define the energy of moving objects thanks to kinetic energy. It’s a beneficial energy to humans. We can harness kinetic energy with renewable energy, sailing boats, and more. Now that we have a clearer understanding of kinetic energy, we can see how greatly it impacts our day-to-day lives from turning on the lights to cooling us down in summer. With kinetic energy explained, we can appreciate how this force of nature improves our lives. 

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