Energy is available on the Earth in different forms. These forms are kinetic energy, potential energy, heat energy, etc. Kinetic energy represents energy in motion. Anything that moves has kinetic energy. It depends on the mass and speed of an object.
In this article, we will focus on kinetic energy, its formula, derivation, types, and how it differs from potential energy. We will also look into some daily-life examples of kinetic energy.
What Is The Kinetic Energy?
Kinetic energy is the energy an object has because of its motion.
If we want to accelerate an object, then we must apply a force. Applying a force requires us to do work. After work has been done, energy has been transferred to the object, and the object will be moving with a new constant speed. The energy transferred is known as kinetic energy, and it depends on the mass and speed achieved.
Kinetic energy can be transferred between objects and transformed into other kinds of energy. For example, a flying squirrel might collide with a stationary chipmunk. Following the collision, some of the initial kinetic energy of the squirrel might have been transferred into the chipmunk or transformed to some other form of energy.
Every moving object and particle have kinetic energy. A person walking, a soaring baseball, a crumb falling from a table and a charged particle in an electric field are all examples of kinetic energy at work.
What is interesting about kinetic energy?
- There are a couple of interesting things about kinetic energy that we can see from the equation.
Kinetic energy depends on the velocity of the object squared. This means that when the velocity of an object doubles, its kinetic energy quadruples. A car traveling at 60 mph has four times the kinetic energy of an identical car traveling at 30 mph, and hence the potential for four times more death and destruction in the event of a crash. - Kinetic energy must always be either zero or a positive value. While velocity can have a positive or negative value, velocity squared is always positive.
- Kinetic energy is not a vector. So a tennis ball thrown to the right with a velocity of 5 m/s, has the exact same kinetic energy as a tennis ball thrown down with a velocity of 5 m/s.
What Are The Three Types Of Kinetic Energy?
Translational Kinetic Energy
Ek=1/2 mv2
is the energy associated with the movement of a chemical entity’s centre of mass, where m is the mass of the chemical entity (molecule, atom, or ion) and v is the velocity of its centre of mass? In the fluid phases (gas and liquids) there will be a distribution of translational energies as different molecules randomly move around each other.
Rotational Kinetic Energy
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).
Vibrational Kinetic Energy
Ek=1/2 kx2
is the energy associated with the atom’s vibrational motion, which can be modelled as an oscillating spring with k being Hooke’s law constant and x is the displacement from the equilibrium location.
That is, even the atoms in a solid, be it a covalent bond or ionic bond (crystal lattice) are not static, and they vibrate back and forth around equilibrium positions like in spring, with the average distance being the “bond distance”.
Note, that atoms oscillate because there are attractive and repulsive forces acting on them which change as their location changes.
For example, in the diatomic hydrogen bond, the nuclei are accelerated towards each other if the attractive forces are greater than the repulsive, but as they get closer and closer, the nuclear/nuclear repulsion becomes stronger, and they start to be repulsed.
As they move farther and farther apart, these forces become weaker, and the attractive forces once again begin to dominate, causing them to approach each other, with the resulting motion like the oscillation of a spring.
Hooke’s law equation describes the potential energy of the oscillator when the distance is maximum from the equilibrium, but as energy is conserved, this is equal to the kinetic energy that atoms feel in the midpoint of the oscillation. The hotter a substance the faster the vibrational frequency.
Examples Of Kinetic Energy
Anything you can think of that has mass (or apparent mass) and motion is an example of kinetic energy. Kinetic energy examples include:
- An airplane has a large amount of kinetic energy in flight due to its large mass and fast velocity.
- A baseball thrown by a pitcher, although having a small mass, can have a large amount of kinetic energy due to its fast velocity.
- A downhill skier traveling down a hill has a large amount of kinetic energy because of their mass and high velocity.
- A golf ball sitting on a tee before it is struck has zero kinetic energy because its velocity is zero.
- A car traveling down the road has less kinetic energy than a semi-truck traveling at the same speed because the car’s mass is much less than the truck’s.
- A river flowing at a certain speed possesses kinetic energy because the water has a certain mass, and it also has velocity.
- An insect flying has a small amount of kinetic energy because its mass and velocity are relatively small.
- An asteroid falling towards Earth exhibits a tremendous amount of kinetic energy due to its large mass and high velocity.
- The act of walking involves the movement of a person’s legs and body, resulting in the possession of kinetic energy.
- When a ball is thrown, it acquires kinetic energy while in motion through the air. The amount of kinetic energy it possesses is determined by the speed of the throw.
- Objects falling towards the ground accumulate kinetic energy due to the force of gravity. The impact’s kinetic energy is directly proportional to the object’s mass and velocity.
- A truck traveling down the road possesses greater kinetic energy compared to a car traveling at the same speed. This is because the truck has a significantly higher mass than the car.