Energy…
What the heck is it? If you look up energy in the dictionary, you’ll likely find a definition such as ‘the capacity to do work’ What’s that? Well, in its most basic state, work means the ability to accomplish a task. So, you’re saying energy is the ability to accomplish a task? Yes, however, let’s get a little more scientific here. Open a chemistry textbook and you might see energy defined as ‘the potential to move matter’. That same textbook would also define work as ‘the energy exchange that results when a force, F, moves an object through distance d; work (w) equals force (F) x distance (d)’. Huh?
Stated another way, energy is the capacity to accomplish work and work is the movement of an object. Got it?
Because energy is the ability to accomplish work, and by our very basic definition, work is movement, energy is measured by the amount of movement it creates. This is called kinetic energy (Ek). We measure the kinetic energy of a system using the following equation:
Ek = ½mv^2
Where:
Ek = the total kinetic energy (movement) of the system
M = the mass, or size of an object. Often measured in kilograms (kg)
V = velocity (speed) at which the object moves. Measured in meters per second (m/sec).
Let’s say a runner has a mass of 59kg and is running at velocity of 4.9m/sec. The runner’s energy can be calculated as follows:
Kinetic energy = ½ x (59.0kg) x (4.9m/s)^2 = 7.08 x 10^2* m^2/s^2
Rather than sticking with the unit of m^2/s^2, the most common unit of energy is the Joule, named after the English Physicist James Prescott Joule. The joule is a technical unit and can be hard to understand so luckily there is another unit of energy we are much more familiar with; the mighty calorie (cal). One calorie = 4.184 Joules.
Finally, one of the most interesting things about energy is that it cannot be created or destroyed. Instead, energy can exist in different forms such as heat and electricity. It can also exist as chemical energy, potential energy, and kinetic energy as already discussed. Here’s the best part; it can even transfer between forms. Below is an example of how the molecule Adenosine Triphosphate (ATP) splits apart to provide energy for muscle contraction. Energy is present in multiple forms during this process:
You are performing a series of squat jumps in the gym. As you lower down, a signal from your brain tells your body to tense your leg muscles. ATP (chemical energy) enters the active site in your muscles and is split by a reaction, releasing its energy. As a result, the muscles in your legs shorten and contract (mechanical energy) as you forcefully propel yourself off the ground (kinetic energy).
This example illustrates how energy changes forms while the total remains constant. In part 2 of this series, we will go deeper on ATP and see how it provides energy that fuels contracting muscle during athletics.
Let me know what you think,
References:
(The American Heritage Dictionary of the English Language. Fourth Edition. Berube, Margery S., 2000.).
Ebbing and Gammon. General Chemistry. Eighth Edition. Charles Hartford, 2005)