To truly grasp kinetic energy, we must first break down potential energy. There are two primary potential energy types.
Elastic potential energy happens when we compress or stretch something, like a spring or an archer’s bow. A bow has potential energy, which increases if you draw its string back. You release kinetic energy when you fire the bow’s arrow.
Gravitational potential energy relates to position and how the Earth’s gravitational force affects an object. An apple on a tree has a certain gravitational potential energy that converts into kinetic energy when it falls from the bough. Put that apple on top of a 300-foot-high pylon, and its potential energy increases because of its position further away from the Earth’s gravitational pull.
These potential energy forms can be broken down further:
Chemical energy is potential energy stored in objects like batteries, coal, natural gas, or biofuels. Chemical reactions release this stored energy.
Nuclear energy is stored in an atom’s nucleus and is released when nuclei are fused or split.
Mechanical energy brings us back to the archer’s bow; the potential energy stored in the string converts into kinetic energy, the flying arrow and wobbling string, once released.
An object’s potential energy helps us understand kinetic energy better.
What Are the Types of Kinetic Energy?
Like potential energy, kinetic energy has two primary types: in this case, translational kinetic energy and rotational kinetic energy.
The translational kinetic energy of an object is the amount of work it requires to take that object from its resting position to a required velocity, e.g., accelerating a parked car to 50 miles per hour. Translational kinetic energy moves an object along a line from one point to another.
Conversely, rotational kinetic energy concerns motion that is centered on an axis. A bike’s wheel has rotational kinetic energy around its axis. Ride that bike in a straight line from A to B, and you’ve converted that rotational kinetic energy into translational kinetic energy.
Other examples of rotational kinetic energy include the Earth orbiting the sun and the moon circling the Earth.
What Are the Main Forms of Kinetic Energy?
Once we have defined the kinetic energy into translational or rotational, there are several types of kinetic energy, the energy of motion.
Electrical energy is moving electrons, often along a wire. The stored energy in a battery becomes kinetic energy when we activate them.
Sound energy is vibrational, meaning it vibrates objects through sound waves, with kinetic energy passing through the wave.
Thermal energy occurs when we move molecules and atoms in substances. They move faster and release heat. We can see thermal energy happening below the Earth’s crust with geothermal energy. It’s worth noting that the Second Law of Thermodynamics states that not all heat energy can be converted into mechanical energy.
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Motion energy is energy that’s stored in moving objects. Think of a car traveling down a road. If it’s involved in a collision, its energy dissipates and spreads dramatically through any objects with which it comes into contact.
Radiant energy, or electromagnetic energy, travels in waves. Examples include visible light, X-rays, and radio waves. Our sun gives off radiant energy, which travels (movement) through space and warms the Earth.
How Do I Calculate an Object’s Kinetic Energy?
We know kinetic energy is the energy of motion. Now let’s see how to calculate the amount of energy an object may have. To find the kinetic energy of an object, we need to know two things: its weight and speed.
- The mass of the object (m) measured in kilograms (kg)
- An object’s velocity (v), measured in meters per second (m/s)
We measure energy in Joules (J). Please note that all the bracketed symbols are SI units, standard metric measurements under the International System of Units (SI). Kinetic energy is a scalar quantity, something with volume or magnitude. Mass is a scalar quantity, while velocity is a vector.
The formula to calculate the kinetic energy of an object is:
KE (Kinetic energy) = ½ mv2
This online kinetic energy calculator can help.
Let’s work on some examples to further our understanding of kinetic energy values.
How Do Speed and Mass Affect Kinetic Energy?
Newton’s Second Law of Motion says the more mass in an object, the more force is required to move it. Think about pushing a model car and a toy car on a flat road or applying force; most of us can push a toy car but not a full-size automobile.
Furthermore, the work-energy theorem has shown that the net work done by forces on an object equals the change in its kinetic energy. Let’s determine how much kinetic energy objects have to demonstrate this proportional relationship.
- A two-ton car (2,000 kg/4,409 lb) traveling 50 miles per hour (mph) has a total kinetic energy value of 499,612 Joules. That same car at 10 mph has 19,984 Joules of kinetic energy.
- A one-pound (454g) toy car traveling at 10 mph has 4.5 Joules of kinetic energy. Let’s speed it up to the speed of sound, 761 mph. Now it has 26,248 Joules of kinetic energy.
We can see how the kinetic energy of a body decreases if it moves more slowly and increases if it moves faster. We can also understand Newton’s Second Law of Motion that net force, or net work, must increase when an object has more mass. It takes more effort to push our real car than the toy car, requiring a more significant amount of work.
What’s also clear is that our heavy automobile going at 50 mph has a lot more energy (499,612 Joules) than at 10 mph (19,984 Joules). As such, the more kinetic energy an object has, the more likely you’ll want to avoid a collision with it. You’d definitely want to duck a toy car going at the speed of sound.
What Is Relativistic Kinetic Energy?
Let’s keep thinking about an object’s speed and how that changes its kinetic energy. According to special relativity, the faster an object moves, particularly at very high speeds, time slows down for that object, and its mass increases.
This slowing of time and increased mass of an object is called its relativistic kinetic energy. Should an object reach the speed of light, then its energy approaches infinite values.
Relativistic kinetic energy is important in our daily lives. GPS satellites move at very high speeds around the Earth, especially compared to the user on the ground. The satellite clocks move more slowly than those on Earth. We use the principles of relativistic kinetic energy to calculate and correct those differences to allow for accurate readings.
What Are the Five Forms of Kinetic Energy?
There are five primary forms of kinetic energy:
- Electrical energy
- Sound energy
- Thermal energy
- Motion energy
- Radiant energy
What Are Examples of Kinetic Energy at Home?
There are many examples of kinetic energy at home. Boiling a kettle of water or heating food in a pan are examples of kinetic energy. The thermal energy that provides heat is actually the byproduct of moving particles. That movement means kinetic energy boils the water.
Eat the food you’ve just warmed, and its potential chemical energy becomes kinetic energy, powering us to move around, talk, and stay warm. Using an electric fan is kinetic energy, with the electricity moving through its wires and the motion caused by its whirling blades.
You walking around your house to alter the thermostat is another example of kinetic energy. Should you drop a glass on the floor, its journey and subsequent smashing is kinetic energy. It regains potential energy once all its pieces come to rest.
A roller coaster is an example of potential and kinetic energy away from home. The wagons gain potential energy as they climb to the track’s highest peak. That potential energy is released as kinetic energy as the roller coaster whooshes down the other side. Following the law of thermodynamics, some energy is lost as friction via the tracks.
What Are Methods to Harness Kinetic Energy?
The fight against climate change may be won or lost thanks to kinetic energy. This energy of movement is present on Earth as wind, the sun’s radiant energy, and the moving water in rivers, oceans, and reservoirs.
We harness the wind to produce electricity at wind turbines. Solar panels and hydropower stations also generate electricity. Geothermal power plants do the same, plus warm our buildings.
Kinetic Energy: Understanding Movement as a Force
Kinetic energy, the energy of movement, is one of the founding blocks of our understanding of the laws of the universe. Objects at rest have potential energy; once they move, they have kinetic energy.
There are many types of kinetic energy impacting our world. Kinetic energy moves us around, keeps us warm, brightens our days with sunshine, and comes at us in the form of great storms. It can even change how much we pay for electricity.
Scientists can calculate the amount of kinetic energy objects have. This information is invaluable. We can estimate the impact of car crashes and design safety features to limit damage, split the atom to access nuclear power, and keep track of our location with GPS thanks to kinetic energy.
We’ve focused on the scientific interpretation of kinetic energy to give an overview of its role. It’s well worth stepping back and observing the beauty and seeming impossibility of kinetic energy in your daily life. From a bird flapping its wings to a crashing wave in the ocean to a three-pointer scored from way downtown, kinetic energy is an impressive force to watch every single day.
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