Mechanical Energy: A Beginner’s Guide to the Energy of Objects and Motion

Mechanical energy is all around us. Whether it’s a kid kicking a soccer ball or a massive wind turbine giving us electricity, there’s no escaping this force. But what exactly is mechanical energy? In this guide, we’ll help you understand more about mechanical energy, how it works and produces power, and why it matters to you (and all of us). 

What Is Mechanical Energy and How Does It Work? 

Mechanical energy is a matter of physical science. It’s the energy of motion, or the energy of an object that moves. All life forms and many systems use mechanical energy to function, and the energy of motion can be seen in everyday life. A few examples are: 

• A child holds a ball up in the air as they scan the field to throw it. They are applying force (holding the ball up) but have not yet exercised any amount of work (force causes displacement of an object).  
• A child kicks a ball (external force) — the force acts upon it, propelling it forward. 
• A ball flies through the air (energy of motion), descends (gravitational force), bounces off the ground to go up again to a point (gravitational potential energy), then comes back down and rolls to a stop. 
• A plane speeding down the runway represents the energy of motion.  
• A speeding airplane slamming into a helicopter transfers kinetic energy to the other aircraft.  
• A private jet slows to stop when the pilot applies brakes (frictional force). 

Mechanical energy (kinetic energy or potential energy) is the energy of either an object in motion or the energy that is stored in objects by their position. 

Mechanical energy is also a driver of renewable energy. Many forms of renewable energy rely on mechanical energy to adequately produce power or convert energy.  

Two examples of renewable energy that depend on mechanical energy are hydropower and wind energy.  

Mechanical energy is just one of several forms of energy, which also include:  

• Light  
• Heat 
• Sound energy 
• Chemical energy 
• Electrical energy 
• Nuclear energy 

Interestingly, all these forms of energy are interchangeable — transferring from one state to another, depending on circumstances. That’s because the scientific law of conservation states that energy never ceases to exist entirely; it can only change from one form to another. 

What Are Some Examples of Mechanical Energy? 

Mechanical energy can be produced by living things, solid objects, gasses, water, or air. There are examples of mechanical energy everywhere.  

Potential and kinetic energy are just two examples that we can see or experience. 

An Example of Potential Energy 

Imagine you arrive home from your local farmer’s market and among your basket of organic goodies is a fat, juicy, round watermelon.  

You place the watermelon on your kitchen counter. It now has potential energy because of its height above the kitchen floor and because of its weight.  

Then, you accidentally bump it with your elbow as you pull out a jar to store your fresh organic coffee beans. You scramble to catch it as the melon begins to roll toward the edge of the counter. This is the energy of motion.  

Because you’ve got your hands full with a jar and a bag of coffee, your melon falls to the floor (gravitational force – an example of nonconservative force), smashing into the ceramic tile and exploding into a gazillion pieces. Now “work” has been done because the impact broke the melon into chunks of juicy mush. The dashed watermelon also creates sound energy, one of the forms of energy discussed earlier. 

An Example of Kinetic Energy 

source

Many of us are excited about clean energy because of its beneficial impact on climate change. We may choose a green energy plan when we select an electricity provider or we might install solar panels in our home. 

When we choose a green energy plan, that energy is often produced by turbines. There are different types of kinetic energy that make the turbines work to produce electricity. 

• Wind: The wind turbine, for example, is a type of renewable energy technology that generates power from air movement. When the wind blows, it spins the turbine’s blades in a circular motion, which turns an electricity-generating drive shaft as it rotates. 
   
• Steam: Similarly, steam turbines utilize pressure to move the arms of a turbine. The blades turn in a circular motion as the steam blows, using mechanical energy to spin a rotator shaft. The rotator shaft is connected to a generator which takes the kinetic energy and converts it into electrical energy. This same process is used to operate steam engines.  
   

• Water: Hydropower acquires the mechanical energy of moving water through hydro turbines or pumped storage systems. Much like wind or steam turbines, hydro turbines use the kinetic energy of flowing water to spin blades. On the other hand, pumped storage systems use water reservoirs at different elevations to move water back and forth and create hydroelectric power. Both methods reflect the naturally occurring mechanical energy forces of rivers, streams, waterfalls, oceans, and even rain. 

Is Mechanical Energy Potential or Kinetic? 

There are two types of mechanical energy – motion (kinetic energy) and stored (potential energy). You can learn more in our guide that explains potential and kinetic energy.  

Mechanical conversion depends on the amount of potential energy an object has and how much kinetic energy it can produce. 

Regardless of potential, however, the energy of motion is an integral part of producing power, and many energy-generating sources could not perform without it.  

Mechanical energy depends on an object’s position and motion, and its power comes from the sum of moving (kinetic energy) and stored (potential) energy. In other words, when an object’s potential energy is combined with its kinetic energy, it creates mechanical energy. 

For example, a roller coaster gains the most gravitational potential energy when it reaches the first peak near the beginning of the ride — that is what establishes the total amount of power available to propel the cars forward for the duration of the ride.  

When ascending to the top of one of its hills or loops, it gains potential energy — the higher it goes, the more potential energy it gets. When it proceeds into a downward motion, it starts converting its potential energy into kinetic energy. As the cart moves down the hill, its kinetic energy increases; simultaneously, its potential energy decreases.  

Some examples of objects with potential energy are a boulder at the edge of a cliff, water in a plugged bathtub, or a wrecking ball waiting to demolish. All of these are in the energy of position before they roll, flow, or swing. 

Kinetic energy sources come from movement or gravitational forces like ocean waves, steam, flowing water, or wind. It can also be the energy exerted when a person runs, jumps, dances, drives a car, or throws a dart, or hurls a bowling ball down an alley.  

When the boulder rolls off of a cliff or the bathtub plug is removed and water begins to rush down the drain, these objects or sources gain kinetic energy.  

As they gather kinetic energy, they lose potential energy, and together the two create an object’s level of force, speed, or power.  

All other energy types can only be kinetic energy or potential energy — one at one time, but never simultaneously. Therefore, mechanical energy is the only form of energy that can harness potential and kinetic energy and change back and forth between both. 

How Does Mechanical Energy Produce Power? 

Mechanical energy is produced by sourcing potential and kinetic energy and turning it into power. Examples of this would be steam, water, wind, gas, or liquid fuels that power turbines.  

Machines are often used to generate other forms of energy through conversion before being used as power. Once mechanical energy is changed a certain way, we can use it the way we want or need it to work.  

Can You Conserve Mechanical Energy? 

You can conserve mechanical energy, which is crucial because energy can escape when used, and power can be wasted during the conversion process. 

Some energy loss is unavoidable when nonconservative or stopping forces or situations occur, but diverting or conserving energy can help attain maximum efficiency. 

Inefficient energy conversion systems cost more to run and can affect the efficiency of power systems. For example, if wind energy is converted into mechanical energy to turn a wind turbine, but the conversion process loses more than half of the energy conducted, the system is slow, more time-consuming, and energy wasting.  

What Is Energy Conversion?  

source

Energy conversion occurs in many different ways. The U.S. Department of Energy gives the operation of a car, for example.  

Gasoline sitting in a car tank before the car is turned on holds chemical potential energy. When the gas is burned after the vehicle is started, it is changed from chemical energy into thermal energy, a form of heat energy.  

The thermal energy is then converted into mechanical energy, using force and motion (kinetic energy) to move the vehicle.  

Once a car no longer needs to move or stops momentarily, brakes are applied which creates friction, a nonconservative force. 

The mechanical, kinetic energy is transformed back into a thermal state and is once again heat energy.  

According to the law of conservation of mechanical energy, when a system is isolated or only interacts with conservative forces, the mechanical energy is constant.  

In other words, the car will retain its mechanical energy constantly until either the gasoline runs out and mechanical energy is no longer produced, or it interacts with a nonconservative force such as friction from braking or a pole, another vehicle, or building. 

Further, if the speed of a moving object or material changes, the kinetic energy changes along with it.  

In the case of the car, if it were to slow down but continue to drive and then crash into another vehicle at only a few miles per hour, the impact would be less than if the car sped up and hit another vehicle when driving as fast as the car could go.  

The faster the movement of a car, the more kinetic energy it is producing and the more power it will exert upon impact.  

Sometimes when objects collide with nonconservative forces like friction, they can also lose energy.  

The amount of energy lost in a collision will depend on what type of collision was encountered when this happens. 

If the collision or interaction is elastic, such as a Slinky toy moving down a staircase, the amount of energy will remain the same, and the object’s power will be conserved.  

If the collision is inelastic, such as the flattened dough of a tortilla landing on a frying pan, the energy will be changed into thermal energy and is not conserved.  

Mechanical Energy Is Everywhere 

The energy of motion is mechanical energy and it can be seen in just about everything we do and experience in life. It’s a baseball player swinging a bat to hit the ball across the field. It’s in a blender as it whirs around, crushing and liquifying our fruit, kale, and ice into a green smoothie. It’s in the brake pedals of a bike as they use friction to stop its wheels turning.   

As energy stored in an object, it can quickly go from potential energy to kinetic energy, and then possibly transform into a different kind of energy altogether as the law of conservation comes into play. Mechanical energy is not as technical as it sounds. It’s a part of everyday life.  

Brought to you by justenergy.com

All images licensed from Adobe Stock.
Featured image: