Mechanical energy also known as the energy of motion is based on how an object moves from its position and motion. Infect 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.
Example Of Mechanical Energy
There are two types of mechanical energy – kinetic energy and potential energy. Any physical object or thing can have mechanical energy, as we shall see in the examples below.
Examples of Kinetic Mechanical Energy
1. A Car Driving Along A Street
Because the car is moving, and it also has a weight, it must therefore have kinetic energy. If the driver takes their foot off the accelerator and puts the car into neutral gear, the car will continue to move, powered by the kinetic energy in the car.
Wind resistance and friction from the road will cause the kinetic energy in the car to gradually get less and less, and the car will keep slowing down until all the kinetic energy has been used up when it will stop completely.
2. A Bowling Ball Rolling Down A Bowling Alley
Again, the ball has a speed and a weight, so it has kinetic energy. That energy keeps the ball rolling along the alley. When it hits the pins, some of the kinetic energy in the ball gets transferred into them, causing them to accelerate quickly and shoot off in different directions.
3. Water Flowing In A River
This one is not so obvious, but the water flowing in a river does have a weight (quite a lot in a large river!) and it is moving, so the water itself has kinetic energy.
Tidal water movements through coastal channels also have a lot of kinetic energy for the same reason. This potential energy can be captured using water wheels and tidal turbines, where it is converted into rotational kinetic energy to be put to use (e.g., for milling or generating electricity).
4. Bullet Fired From A Gun
Bullets weigh very little (low mass) so you would think that they don’t have much kinetic energy, but because their velocity is so high and due to the squaring, bullets contain a huge amount of kinetic energy. The kinetic energy contained in a bullet means it is very hard to stop, and it will penetrate many other kinds of objects. For a bulletproof material to bring a bullet to a complete stop, it has to absorb all its kinetic energy in one go.
5. Wind
Another one that’s not so obvious: air itself has mass, and so large volumes of air moving around (commonly known as wind!) have kinetic energy. This kinetic energy can be transferred into a wind turbine through its blades, where it is stored as rotational kinetic energy.
6. A Person Walking Or Running
When you walk or run, chemical energy that is stored in your body is converted into kinetic energy as you move. The faster you run, the more chemical energy is converted into kinetic energy, and the more tired you feel!
7. A Flywheel Spinning Round
A flywheel is a large heavy wheel designed to store kinetic energy. They were commonly used in old steam engines to stabilize the jerky motion from the output of the steam-driven pistons. Because they are heavy, flywheels take a lot of energy to get going, but once they’re spinning, they contain a lot of kinetic energy.
Examples of Potential Mechanical Energy
1. A Stretched Spring
As a spring is stretched out, it gains potential mechanical energy in the form of strain in the spring. The strain wants to make the spring return to its original shape. The more it is stretched out, the more potential energy it stores, and the harder it becomes to stretch it further.
When it is released, the potential energy is given out as it returns to its original shape. If a spring is stretched too far, it goes past what is called the spring’s elastic limit and the spring’s material (metal or plastic or whatever the spring is made of) fails, meaning it will never return to its original shape.
2. A Roller Coaster Carriage At The Top Of A Hill About To Go Down It
Roller coaster carriages are lifted up to the top of the lift hill using a chain. Kinetic energy is transferred into the carriage from the chain, and as it gets higher, the carriage has more and more potential energy.
This kind of potential energy is also called gravitational potential energy because it relies on gravity to pull the carriage down once it has reached the top of the hill.
3. A Bent Bow About To Fire An Arrow
In a similar way to a stretched spring, a bent bow stores potential energy in the strain of the bow as it wants to return to its usual shape. When the archer releases the bowstring, the potential energy in the bow is converted into kinetic energy in the arrow, causing it to fly towards its target.
4. Water In The Upper Lake Behind A Hydroelectric Dam
In another example of gravitational potential energy, the lake of water behind a hydroelectric dam has potential energy, because it is higher up than the outlet on the other side of the hydroelectric dam.
When the sluice gates are opened, gravity causes the water to flow out of the upper lake down through the internal pipes, whereupon the potential energy is converted into linear kinetic energy in the water.
The water flows through the generation station, where its kinetic energy is converted into rotational kinetic energy in hydroelectric turbines, and from there into electrical energy.
Everyday Examples of Mechanical Energy
Mechanical energy is one of the only types of energy that is easy to see. If something is moving, it is using mechanical energy! Take a look at these sources of mechanical energy that you’re likely to find in the home.
- Turning a doorknob
- Breathing in and out
- Hammering a nail
- Riding a bicycle
- Sharpening a pencil
- Using kitchen appliances
- Listening to music
- Typing on a keyboard
- Driving a car
- Exercising
Take a look around you. Any object that is moving is using kinetic mechanical energy. Even objects that are not moving are storing potential mechanical energy. When you move something with your hand, you’ve transferred kinetic mechanical energy from your body to the object you are moving.