What is energy? | HowStuffWorks
Imagine a basketball. An ordinary, everyday basketball, perfectly still on an empty court. Now visualize a player – let’s go with Diana Taurasi of the WNBA’s Phoenix Mercury. She heads for the middle of the field, her shoes squeaking against the hardwood boards. Then Taurasi bends down, grabs the ball, gets up and lifts it above his head.
You just witnessed a rise in the ball potential energy.
For the record, this is just one of many types of energy that we encounter on a daily basis. There is also kinetic energy, electrical energy, thermal energy, etc.
This raises a fundamental question. Scientifically, what is energy? What does this word mean in the context of physics, chemistry, engineering and related STEM fields?
Here’s the definition you’re most likely to hear in your advanced level courses or find in a textbook:
“Energy is the ability to do work.”
Taken by itself, this phrase may seem vague and not particularly helpful. But don’t worry, we’re here to help you unbox it.
Now, when textbooks say energy is “the ability to do work”, they’re not just talking about a 9 to 5 job. In a nutshell, the scientific meaning of the word “work” is the process of moving an object by applying a force to it.
“Whenever a force is applied to an object, causing the object to move, work is being done by the force,” according to Boston University.
As for energy, it comes in two main categories: kinetic energy and potential energy.
KE goes to Hollywood
Sometimes kinetic energy is described as “the energy of motion”. To possess this kind of energy, an object must be moving.
Remember the Texas-sized asteroid that headed for Earth in Michael Bay’s 1998 blockbuster “Armageddon”? In real life, this thing would have had some serious kinetic energy. The same goes for speeding cars, falling apples, and other moving objects.
Grab a pencil, folks, because we’re about to throw an equation at you:
KE = (1/2)mxv2
Translation: An object’s kinetic energy (“KE”) is equal to half its mass (“m”) multiplied by its velocity squared (“v2“).
Time to break this down with an example. What is the kinetic energy of a 400 kilogram (or 882 pound) horse galloping at a speed of 7 meters per second (23 feet per second)?
Expressed numerically, this is what the problem looks like:
KE = (1/2) 400 x 72
Plug in the numbers and you will find that the kinetic energy possessed by our noble steed is equal to 9800 joules. For the record, joules (abbreviated as “J”) is a unit of measurement used by scientists to quantify energy or work.
So much potential
If kinetic energy is “energy of motion”, then potential energy is “energy of position”.
Let’s go back to Diana Taurasi. What do you think will happen the moment she drops that ball, the one that was said to have lifted off the ground?
Of course, it will fall and hit the hardwood floor. All because of a little thing called gravity. (To keep things simple here, we’re assuming the WNBA star hasn’t been actively pushing or throwing the ball.) And as we now know, the moving object will feature kinetic energy coming down.
But before the drop, before the ball leaves the hands of Taurasi, it will contain a lot of potential energy.
Potential energy is stored energy. It is the energy that an object (Taurasi’s ball in this case) has due to its position relative to other objects, such as solid ground. Why is this phenomenon called “potential energy”? Because it introduces potential for a force – such as gravity – to do work.
Neither created nor destroyed
Note that there are different kinds of potential energy. The one we talked about in our basketball example is called gravitational potential energy or simply “gravitational energy”.
To quote the US Energy Information Administration website, it is a type of potential energy “stored in the height of an object. The taller and heavier the object, the more gravitational energy is stored”.
By lifting her ball off the ground, Taurasi gave gravity the potential to work with her. If she had done like a Harlem Globetrotter and carried the ball to the top of a large circus ladder – or if she had lifted a heavy bowling ball instead of a light basketball – there would be even more energy. gravitational potential at play.
Notice that this energy won’t simply disappear when Taurasi drops the ball. Within the confines of a closed system (like our universe), energy can neither be created nor destroyed. It’s simply transforms.
As it dives towards the hardwood, this ball gravitational potential energy will decrease because it gets closer to the ground. And upon hitting the ground, the ball (functionally) will have no gravitational potential energy.
Yet, as the ball zooms downward and loses gravitational potential energy along the way, there will be a simultaneous increase in its kinetic energy.
Our story doesn’t end once the ball hits these floorboards. Part of its energy will be converted into thermal energy and thus generate heat.
Oh, and that cute basketball sound they make when they bounce? It is also a kind of energy, the one that most people call sound.
Other types of energy include electric energy, mechanical energy and radiant energy.
Before we part, we’ll leave you with some last-minute definitions.
- thermal energy: It refers to the internal movement and vibration of atoms and molecules inside an object or substance. When thermal energy flows Between objects or substances, we call this transfer “heat”.
- Sound: This is the energy caused by vibrations and which moves through substances in longitudinal waves.
- Electric energy: A type of kinetic energy, it is the movement of electric charges that can occur when a force is applied to atoms.
- radiant energy: This is the kind of energy you get from electromagnetic radiation. Light falls into this category.
- chemical energy: File this one under “potential energy”. It is the energy stored in the bonds that hold the atoms together.
- gravitational energy: Also called “gravitational potential energy”, it would be the potential energy that an object derives from its placement in space subject to gravity.