Kinetic energy is often referred to as the energy in motion. In other words, any moving object has kinetic energy.
This article is devoted to kinetic energy, more specifically some common energy examples we come across in our daily lives. You will find here listed 10 examples of kinetic energy at home.
Basic facts about kinetic energy
Ek = ½mv2
Kinetic energy (Ek) is half of the product of the mass of the object ‘m’ and the square of its velocity ‘v’. As energy is a physical quantity that can be completely described by its magnitude, it is a scalar quantity just like distance, volume, and time. It is not dependent on the direction of motion of the object. Because of this, energy always remains positive.
When you double the mass of the object, the kinetic energy is doubled. However, when you double the velocity of its motion, the energy is quadrupled.
Kinetic energy may appear in objects in basically three forms based on how the object is moving. These are:
- Rotational kinetic energy: This is the kinetic energy associated with the rotational movement of the object. The Earth rotating on its axis is an example of rotational kinetic energy.
- Vibrational kinetic energy: This is the kinetic energy formed due to the vibrations of the object. A vibrating phone and a batter head when hit with a stick are good examples of vibrational kinetic energy.
- Translational kinetic energy: This is the kinetic energy formed due to the displacement of the object from one position to another. A bus in motion and a ball falling from a height are examples of translational kinetic energy.
The SI unit of kinetic energy is Joule (J). Like other forms of energy, kinetic energy can be transmitted between objects and converted to and from other energy forms such as mechanical energy, potential energy, and chemical energy. When we use food to fuel our activities, the chemical energy from the food is converted to kinetic energy to help us move.
Let’s understand kinetic energy through some examples. Here are a few examples of kinetic energy in your home.
Examples of kinetic energy at home
The formula Ek = ½mv2 decides the quantity of kinetic energy any moving object will have. Here are a few examples of kinetic energy in your house. These are found in everyday objects we come across at home. Though we may see these objects often, we may have never thought of them as examples of kinetic energy.
So, here we go.
1. When you walk
Here, the object is ourselves. When we walk, we are moving from one position to another. So, we should possess translational kinetic energy. Do you know that it is because of the kinetic energy generated while walking that we feel hot?
This kinetic energy comes from the chemical energy present in the foods we eat. When the food we eat is digested and processed, glucose is released. Excess glucose produced is stored in muscles and the liver for later use.
2. When you throw a ball up
A stationary ball has no kinetic energy. When you throw the ball, you impart kinetic energy to it by converting your own chemical energy present in the muscles. Once you release the ball, the gravitational force will act on it and slow it down.
As the ball goes up in the air, kinetic energy in it will get converted to potential energy. When it reaches the maximum height, it will have no kinetic energy and only potential energy. However, when it descends, the potential energy will again be converted to kinetic energy.
The moment before it hits the ground, the ball will have maximum kinetic energy and minimum potential energy. Once it becomes stationary, all its kinetic energy will get transformed into potential energy.
3. When you drop an object
The energy transformation while throwing and dropping are entirely different. When throwing, you are imparting your energy to the object, while dropping, its kinetic energy starts from zero. The energy of a completely motionless object is stored as potential energy. So, the moment you drop the object, it will have only potential energy and no kinetic energy.
As the object slips from your hand, it will fall to the ground due to gravitational force. As it falls, its velocity increases gradually, increasing its kinetic energy and bringing down its potential energy. The moment before it hits the ground, its kinetic energy is at its maximum and potential energy is almost nil.
When the object hits the ground, kinetic energy gets released. When it comes to a standstill, the object will have no kinetic energy and only potential energy.
4. When you boil water
As you already know, all objects are made of molecules and atoms. Water has water molecules with both hydrogen and oxygen atoms in it. When you heat water, water molecules begin to move faster and start spreading out. As they start moving faster and faster, they will collide with each other, creating thermal energy.
As thermal energy is generated as a result of the motion of molecules and atoms, it is considered a form of kinetic energy. It is an indicator of the activity of molecules and atoms in an object. As the water gets hotter, the kinetic energy of molecules keeps increasing until it boils.
5. When you cycle or skateboard
Before you start moving, your cycle or skateboard is at rest. So, its kinetic energy will be nil. And potential energy at its maximum. As you apply force and pedal your cycle or move the skateboard, its kinetic energy starts increasing.
For calculating the kinetic energy of a moving cycle or skateboard, you need to add your weight to the weight of the cycle or skateboard as you are moving along with it. This means as it moves forward a considerable amount of kinetic energy is produced.
6. When you play music
Sound is energy moving through a medium, like air or water. It is generated by vibrations. These vibrations create disturbances in the medium and are transmitted as waves. When the sound waves reach our eardrum, it again causes vibrations, which are interpreted by our brains as sound.
Any sound-generating source acts in the same way including the speakers you have at home. In fact, the same is true when you speak as well. When you switch on the speaker, it will generate sound as vibrations in the air. You can feel the vibrations by placing your hand on the speaker. These air molecules possess kinetic energy.
7. When you switch on an incandescent bulb
In the old-fashioned light bulb, electricity is transmitted from one metal to another by contact. As you may already know, electricity is the flow of electrons. As the electricity travels through copper wires, electrons gain kinetic energy. When the electricity reaches the tungsten filament of the bulb, electrons will have high amounts of kinetic energy.
These electrons packed with kinetic energy will hit the atoms of the tungsten filament, transferring their energy to the filament. As a result, the filament gets heated to a point where it begins to emit light energy or photons. Photons are described as tiny light packets.
The sunlight is also made up of similar small “packets of light” or photons. An incandescent bulb also converts some of the electrical energy into heat energy. Both light and heat energy produced by the bulb are forms of radiant energy, which is transmitted as waves.
8. When you stand in the sun
The Sun is the energy source for our planet earth. In the sun, energy is created by nuclear fusion. During this process, vast amounts of light and heat energy are produced, which is then radiated into space. Some of it reaches us on earth. This is called solar radiation. It is a form of radiant energy, a form of kinetic energy created when electromagnetic waves travel through space.
When sunlight falls on you, the electromagnetic waves make the molecules of your skin move faster, thus creating kinetic energy. This is the reason why you feel hot when standing in the sun.
9. When you use a battery
A battery converts chemical energy into electrical energy. During this process, electrons move from the anode (negative electrode) to the cathode (positive electrode). This flow of electrons constitutes an electric current. As the electrons move, they gain kinetic energy.
When a rechargeable battery is being charged, the direction of the flow of electrons is reversed. It moves from cathode to anode. Again, as the electrons move, they gain kinetic energy.
10. When you fire a gun
As you pull the trigger in a gun, the spring mechanism helps the metal firing pin strike the primer located at the back end of the cartridge. This results in causing a spark in the primer, which in turn ignites the propellant or the gunpowder. As the gunpowder burns, large quantities of gas are released resulting in an explosion. This will propel the bullet out of the cartridge at great speed. The rifling of the barrel will add a spin to the bullet, increasing its speed as it gets ejected from the barrel.
From the firing pin to the bullet traveling through the air, the firing of a gun involves many movements. During each one of these movements, kinetic energy is produced. The bullet ejected by the gun at great speed will have very high kinetic energy, also known as muzzle energy. In fact, the muzzle energy of the bullet determines how deadly the gun is.
From the formula, Ek = ½mv2, we know that the higher the mass/weight of the bullet and the faster it travels, the higher its muzzle energy or more destructive it will be.
Final thoughts on kinetic energy at home
Anything that moves has kinetic energy in some form or the other. This movement need not always be visible to us, as in the case of electricity, light, or heat. Often, the kinetic energy generated gets converted into heat energy as in the case of rubbing hands.