What is Mechanical Energy?

Definition: Mechanical energy refers to the energy that a body possesses by virtue of its motion or position. It is a type of energy that is related to the physical movement and position of an object.

Additionally, it is a fundamental concept in physics and is essential for understanding various phenomena, such as the behaviour of moving objects, the efficiency of machines, and the conservation of energy.

Mechanical energy is best understood as the energy of motion. It encompasses both kinetic energy, which arises from the motion of objects, and potential energy, which is associated with an object’s position. To illustrate this concept, consider a ball thrown into the air. As it rises, it possesses kinetic energy due to its motion. At the same time, it accumulates potential energy as it climbs higher in the gravitational field.

The relationship between kinetic and potential energy is fundamental to comprehending the concept of mechanical energy. As the ball rises and its potential energy increases, its kinetic energy decreases. However, this doesn’t mean that the total mechanical energy of the system changes; instead, it remains constant, illustrating the conservation of energy.

Understanding Mechanical Energy

Let me give you an example. Imagine you are on a playground and you are on a swing. When you first start swinging, you don’t move very fast, but as you keep swinging, you start moving faster and faster. That’s because you have energy that’s making you move, and we call that mechanical energy.

Mechanical Energy: Definition and Types
Mechanical Energy: Definition and Types

Moreover, did you know that mechanical energy is all around us? It’s what makes things move and it’s what helps us to do work. It’s also a really important concept in science and engineering.

For example, understanding mechanical energy can help engineers design better cars that use less fuel. This is really important because cars use a lot of energy and can produce a lot of pollution. Hence, by designing cars that are more efficient, we can reduce the amount of energy we use and help protect the environment.

Mechanical Energy: Definition and Types

Total Mechanical Energy

Total mechanical energy refers to the sum of an object’s potential energy and kinetic energy. In other words, it represents the total amount of energy that an object possesses due to its position or motion.

The formula for total mechanical energy can be written as:

Total mechanical energy (E) = Potential energy (U) + Kinetic energy (K)

And

Potential energy (U) = mgh,

where

m = the mass of the object,

g = the acceleration due to gravity, and

h = the height of the object above a reference point.

Additionally,

Kinetic energy (K) = (1/2)mv2,

where

m = the mass of the object and

v = the velocity of the object.

Now, since we know that E = U + K

Therefore, we can write the formula for total mechanical energy as:

E = U + K = mgh + (1/2)mv2

Hence,

E = mgh + (1/2)mv2

Where E is the total mechanical energy of the object. The S.I unit of total mechanical energy is in Joules (J)

Types of Mechanical Energy

We have 2 types of mechanical energy:

Potential Energy

Potential energy is the energy an object possesses due to its position. We can also define potential energy as energy by virtue of the position of an object. Hence, it is energy that an object can store when it is at rest or not moving. For instance, think about a ball that’s sitting at the top of a hill. It’s not moving, but it has the potential to move and when it starts rolling, it has kinetic energy.

Here is another example. Did you know that the higher an object is, the more potential energy it has? For example, a book on a shelf has potential energy because it has the potential to fall to the ground. Therefore, the higher the book is on the shelf, the more potential energy it has.

Books sitting on a shelf due to potential energy
Books sitting on a shelf due to potential energy

Similarly, a stretched rubber band has potential energy because it has the potential to snap back to its original shape. By using the potential energy of water from hydropower stations, we can generate electricity without relying on fossil fuels.

Potential energy can play a big role in renewable energy sources. For example, hydropower is a type of renewable energy that uses the potential energy of water to generate electricity. According to the International Energy Agency, in 2019, hydropower accounted for 16% of the world’s electricity generation.

Another example of using potential energy in renewable energy sources is wind power. Wind turbines use the potential energy of wind to generate electricity. According to the U.S. Energy Information Administration, in 2020, wind power accounted for 8% of the electricity generated in the United States. By using the potential energy of wind, we can generate electricity without relying on non-renewable sources.

Formula and Unit of Potential Energy

The formula for calculating potential energy of a body is

Potential energy (P.E) = Mass (m) x force of gravity (g) x height (h)

Which implies that

P.E = mgh

The S.I unit of potential energy is in Joules (J)

Types of Potential Energy

We have two types of potential energy, and they are Gravitational and Elastic potential energy.

Gravitational Potential Energy (U)

Gravitational potential energy is the energy that is stored in an object when it’s high up above the ground. The higher an object is, the more gravitational potential energy it has. The formula for calculating gravitational potential energy is

U = mass (m) x gravity (g) x height (h)

Therefore, the more mass an object has, the higher it is, and the stronger gravity is, the more gravitational potential energy it has.

For example, the Hoover Dam on the Colorado River generates enough electricity to power about 1.3 million homes. By using the gravitational potential energy of water, we can generate electricity without relying on non-renewable sources.

Elastic Potential Energy (UE)

Elastic potential energy is the energy that is stored in an object when it’s stretched or compressed. For example, a stretched rubber band has elastic potential energy. The formula for calculating elastic potential energy is

UE = (1/2) x spring constant (k) x distance squared (x2)

UE = (1/2) kx2

Thus, the more we stretch or compress the spring, the stronger the spring constant is, and the more elastic potential energy it has.

Elastic potential energy is important in many different fields, including engineering and physics. For example, we use it in bungee jumping, where we use the elastic potential energy of the bungee cord to safely slow down a jumper.

Solved Problems for Potential Energy

Problem 1

A 2kg object is lifted to a height of 10 meters above the ground. What is its gravitational potential energy?

Answer:

The formula for gravitational potential energy is mass x gravity x height.

U = mgh

Plugging in the given values, we get:
U = mgh = 2 x 9.8 x 10 = 196 joules
Therefore, the object has 196 joules of gravitational potential energy.

Problem 2

A spring has a spring constant of 20 N/m and is compressed by 0.1 meters. What is it’s elastic potential energy?

Answer:

The formula for elastic potential energy is (1/2) x spring constant x distance squared.

UE = (1/2) kx2

Plugging in the given values, we get:
Potential energy = 0.5 x 20 N/m x (0.1 m)2 = 0.1 joules
Therefore, the spring has 0.1 joules of elastic potential energy.

Problem 3

A roller coaster car has a mass of 500 kg and is at the top of a hill that is 50 meters high. What is its total potential energy?

Answer: The total potential energy of the roller coaster car is the sum of its gravitational potential energy and its elastic potential energy (if applicable).

Since the roller coaster car is not compressed, it only has gravitational potential energy. Using the formula for gravitational potential energy, we get:

Potential energy = mass x gravity x height

U = mgh = 500 x 9.8 x 50 = 245,000 joules = 245 kj
Therefore, the roller coaster car has 245 kilojoules of total potential energy.

Examples of Potential Energy in Everyday Life

Here is an explanation of some common examples of potential energy in everyday life in a tabular form:

Type of Potential EnergyExamplesExplanation
Gravitational Potential EnergyA ball on a shelf, water in a dam, a book on a tableGravitational potential energy is the energy that an object has due to its position above the ground. The higher the object is, the more potential energy it has. Water in a dam has gravitational potential energy because it has the potential to flow down and turn turbines to generate electricity.
Elastic Potential EnergyA stretched rubber band, a compressed spring, a bow, and an arrowElastic potential energy is the energy that is stored in an object when it is stretched or compressed. When the object is released, it will bounce back to its original shape and release the stored energy. A compressed spring has elastic potential energy because it has the potential to bounce back to its original shape. A bow and arrow have elastic potential energy because the string is stretched back, and when released, it propels the arrow forward.
Chemical Potential EnergyFood, batteries, gasolineChemical potential energy is the energy that is stored in the bonds between atoms and molecules. When the bonds are broken, energy is released. For example, food has chemical potential energy because the bonds between the atoms in the food can be broken down during digestion, releasing energy for the body to use. Batteries have chemical potential energy because the chemical reactions inside the battery produce energy. Gasoline has chemical potential energy because the energy is released when it is burned in an engine.
Potential Energy in Everyday Life

Kinetic Energy

Kinetic energy. Which is the energy an object possesses due to its motion. So, when you are swinging on the playground, you have kinetic energy because you’re moving. Did you know that the faster an object is moving, the more kinetic energy it has?

Therefore, it is the energy that is produced when an object moves, and it is determined by the object’s mass and velocity. The faster an object is moving, the more kinetic energy it has. Likewise, the heavier an object is, the more kinetic energy it has.

For example, a car driving down the road has kinetic energy because it’s moving. The faster the car is going, the more kinetic energy it has.

Kinetic Energy Formula and Unit

The formula for calculating kinetic energy is

K.E = (1/2)mv2

Where:

K.E = kinetic energy

m = mass of the object

v = speed or velocity of the object

The S.I unit of kinetic energy is in Joules (J)

Fun Facts About Kinetic Energy

Here are some fun facts about kinetic energy that might interest you:

  1. Kinetic energy can be in many different forms, from the movement of vehicles and machines to the flight of a bird or the movement of your body when you run or jump.
  2. The amount of kinetic energy an object has is directly proportional to its mass and the square of its velocity. Hence, doubling an object’s velocity will quadruple its kinetic energy.
  3. Kinetic energy can be transferred from one object to another. For example, when a ball is thrown, the kinetic energy from the thrower’s hand is transferred to the ball, causing it to move.
  4. We can use the kinetic energy of an object to do work, such as lifting or moving other objects. This is why we often use heavy types of machinery, like cranes and bulldozers for construction and transportation.
  5. Another application of kinetic energy involves generating electricity in hydroelectric power plants and wind turbines. The spin of turbines is due to the movement of water or wind, which generates kinetic energy that is then converted into electrical energy.

Examples of Kinetic Energy in Everyday Life

Five examples of kinetic energy in everyday life:

  1. Playing with a ball: When you throw a ball, it has kinetic energy because it is in motion. The harder you throw it, the more kinetic energy it has. When the ball hits the ground or another object, some of its kinetic energy is transferred to that object, causing it to move.
  2. Riding a bike: When you pedal a bike, you are using your energy to make it move. As the bike moves, it gains kinetic energy. The faster you ride, the more kinetic energy the bike has. When you apply the brakes to slow down or stop the bike, some of the kinetic energy is converted into other forms of energy, such as heat and sound.
  3. Watching a rollercoaster: The design of rollercoasters makes it necessary to use potential energy (stored energy due to gravity) to gain kinetic energy as they move down hills and through loops. As the rollercoaster moves, it gains more and more kinetic energy, which is what makes it feel fast and exciting.
  4. Jumping on a trampoline: When you jump on a trampoline, you are using your energy to make yourself move. As you jump higher and higher, you gain more kinetic energy. When you land on the trampoline, some of the kinetic energy is transferred back to the trampoline, causing it to bounce you back up again.
  5. Listening to music: When you listen to music, the sound waves produced by the speakers have kinetic energy because they are moving through the air. This kinetic energy is what allows you to hear the music and feel the bass in your chest.

How to Solve Kinetic Energy Problems

Problem 1

A baseball with a mass of 0.145 kg is thrown at a velocity of 40 m/s. What is its kinetic energy?

Solution:

Using the formula

K.E = (1/2)mv2,

we can calculate the kinetic energy of the baseball as follows:
KE = (1/2)mv2 = 0.5 x 0.145 x 402 = 116 J

Therefore, the kinetic energy of the baseball is 116 Joules

Problem 2

A rollercoaster with a mass of 500 kg is moving at a velocity of 25 m/s. What is its kinetic energy?

Solution:

Using the formula

K.E (1/2)mv2,

we can calculate the kinetic energy of the rollercoaster as follows:
KE = (1/2)mv2 = 0.5 x 500 x 252 = 156,250 J

Thus, the kinetic energy of the rollercoaster is 156,250 Joules.

Problem 3

A car with a kinetic energy of 100,000 J is moving at a velocity of 30 m/s. What is its mass?

Solution:

Rearranging the formula KE = (1/2)mv2 to solve for mass, we get:
m = (2 x KE) / v2
Substituting the given values, we get:
m = (2 x 100,000) / 302 = 222.22 kg

Therefore, the mass of the car is 222.22 kilograms

Table – Similarities and Differences Between Potential and Kinetic Energy

Below is a tabular comparison of potential and kinetic energy:

Energy TypePotential EnergyKinetic Energy
DefinitionThe energy that an object has due to its position or stateEnergy of motion
ExamplesA ball held up in the air, a stretched rubber band, water at the top of a waterfallA moving car, a spinning top, a person running
SimilaritiesAll potential energy involves stored energy that can be converted into other forms of energyAll kinetic energy involves objects in motion
DifferencesThe type of potential energy depends on the object’s position or stateThe amount of kinetic energy depends on the object’s mass and velocity
comparison of potential and kinetic energy:

As you can see, the two types of energy involve movement or stored energy that can be converted into other forms of energy. The main differences between them are the source of the energy and how it is expressed. Potential energy depends on an object’s position or state, while kinetic energy depends on an object’s motion.

Understanding the similarities and differences between these types of energy is important because it helps us to better understand how energy works and how it can be used. For example, we can use potential energy to power a car by storing energy in a battery, and then use kinetic energy to actually move the car. And we can use sound energy to communicate with each other or to enjoy music and other forms of entertainment.

By learning more about potential and kinetic energy, we can appreciate the different ways that energy exists and how it affects our daily lives.

Mechanical Energy: Potential or Kinetic?

Distinguishing between potential and kinetic energy is essential. Potential energy relates to an object’s position, while kinetic energy pertains to its motion. The conditions in which each type of energy predominates can be best understood through various real-world examples.

For instance, consider a pendulum. When the pendulum reaches its highest point, it possesses maximum potential energy and minimal kinetic energy since it is momentarily at rest. As it swings downward, the potential energy is converted into kinetic energy, reaching its peak as the pendulum passes through its lowest point.

This transformation is evident in celestial bodies, such as the Earth-Moon system. In an elliptical orbit, the Earth’s gravitational potential energy is highest when it is farthest from the Moon and lowest when it is closest. As the Earth moves along its orbital path, it exchanges potential energy for kinetic energy and vice versa, maintaining the mechanical energy of the system.

Examples of Mechanical Energy

To understand mechanical energy better, let’s delve into some practical examples. Imagine a demolition crew preparing to bring down a building. They employ a massive wrecking ball, suspended high in the air. As the ball is released, it transforms its stored potential energy into kinetic energy, swinging with incredible force and destroying the structure upon impact.

Another example can be found in the world of sports, such as bowling. When you roll a bowling ball down the lane, it initially has potential energy due to its elevated position. As it moves forward, this potential energy is converted into kinetic energy, giving the ball the ability to knock down pins.

In the context of a dart gun, the elastic potential energy stored in the stretched rubber band is converted into kinetic energy when the dart is released, propelling it forward with great speed. These examples showcase how mechanical energy is involved in various physical systems and transitions between kinetic and potential forms.

Importance of Understanding the Different Types of Mechanical Energy

We earlier gave an example of fuel consumption in our cars. But it’s not just cars that use mechanical energy. Did you know that wind turbines use mechanical energy too? Wind turbines are machines that convert wind energy into electrical energy. Understanding mechanical energy helps engineers design more efficient wind turbines that can produce more electricity with less wind.

According to the International Energy Agency, the world’s energy demand is expected to grow by 4.6% in 2022 . That means we’re going to need more energy to power our homes, schools, and businesses. By understanding mechanical energy, we can find ways to use energy more efficiently and reduce our dependence on fossil fuels.

In fact, a study by the National Renewable Energy Laboratory found that wind energy has the potential to meet the world’s electricity demand 40 times over. That’s a lot of energy! By investing in wind energy, solar energy, and other renewable energy sources, we can reduce our dependence on fossil fuels and protect the environment.

Renewable Energy Sources as Mechanical Energy

According to the U.S. Energy Information Administration, in 2020, 80% of the energy consumed in the United States came from fossil fuels. Fossil fuels are a non-renewable energy source, which means that they will eventually run out. This is why it’s so important to understand the different types of mechanical energy.

Additionally, another study by the National Renewable Energy Laboratory found that wind energy has the potential to provide 35% of the electricity used in the United States by 2050. Therefore, if we focus on renewable energy sources and understand the different types of mechanical energy, we can create a more sustainable future for ourselves and for the planet.

How Does Mechanical Energy Produce Power?

The conversion of mechanical energy into power plays a pivotal role in our daily lives. Power is the rate at which energy is transferred or converted, and it is an essential aspect of numerous technologies and machines. Understanding how mechanical energy is converted into power provides insight into the devices and systems we rely on.

Consider the case of a wind farm. Wind turbines harness the kinetic energy of moving air, converting it into electrical power. As the wind blows, it sets the turbine blades in motion, which, in turn, drives a generator. The rotation of the generator produces electricity. In this way, the kinetic energy of the wind is transformed into electrical power, which can then be used to light our homes, power our appliances, and more.

Mechanical energy can also be converted into power through various other mechanisms, such as the engine of an automobile. When you start your car’s engine, it burns fuel to produce mechanical energy that powers the vehicle. The engine’s pistons move, and this motion is harnessed to turn the wheels, propelling the car forward.

Can You Conserve Mechanical Energy?

Conserving mechanical energy is of paramount importance for several reasons. Firstly, it contributes to the efficiency of mechanical systems. The less energy that is lost due to friction, air resistance, or other dissipative forces, the more efficient a machine becomes.

Practical tips for conserving mechanical energy include maintaining and lubricating moving parts to reduce friction, streamlining the design of vehicles to minimize air resistance, and choosing energy-efficient appliances for your home. These measures not only help reduce energy waste but also save you money in the long run.

Energy Conversion

Energy conversion is a key concept when discussing mechanical energy. It refers to the transformation of one form of energy into another. To illustrate this, let’s consider the operation of a car. When you press the accelerator pedal, the car’s engine converts chemical potential energy stored in fuel into kinetic energy.

This conversion process allows the car to accelerate and move. As the car travels, some of its kinetic energy is lost to dissipative forces like friction and air resistance. However, the car’s braking system can recover some of this kinetic energy by converting it back into potential energy stored in the brakes. This regenerative braking system is an excellent example of how energy conversion can be applied in everyday technology.

Mechanical Energy Is Everywhere

It’s worth noting that mechanical energy is not limited to specific scenarios or industries. In fact, it’s all around us, often in ways that we might not immediately recognize. As you read this article, you are likely sitting or standing in a building that relies on mechanical systems to function efficiently. The electricity powering your devices is generated through the conversion of various forms of energy, including mechanical energy in the case of wind turbines and hydroelectric dams.

Even the act of walking, a seemingly simple and everyday task, involves the conversion of mechanical energy. With each step you take, you are utilizing the energy stored in your muscles to propel your body forward, overcoming the gravitational force that seeks to pull you downward.

Importance of Studying Energy in Science and Engineering

Energy is incredibly important in science and engineering because it is what makes things work! Energy is the ability to do work or create change, and without it, nothing would work. For example, without energy, a car wouldn’t be able to move, a light bulb wouldn’t be able to glow, and your body wouldn’t be able to move or think.

By studying energy, scientists and engineers can learn how to harness it to create new technologies and improve existing ones. They can also learn how to make energy use more efficient, which means using less energy to achieve the same result. This is important because it can help us to conserve resources and protect the environment.

In science, energy is studied in many different fields, including physics, chemistry, and biology. Scientists use energy to explain how things work and to understand the natural world around us. For example, they use energy to explain how the sun produces light and heat, and how plants convert sunlight into food through a process called photosynthesis.

In engineering, energy is used to design and create new technologies. Engineers use energy to power machines and devices, and to make them more efficient. They also work to find new ways to produce energy, such as through wind or solar power.

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Reference

Elastic Potential Energy