Work, Energy & Power

As a rule of thumb, you’re using energy all the time. But what exactly is energy? And what do physics terms like “work” and “power” actually mean?

Let’s take a step back from the calculator and just understand the story: how motion and force become action, how energy changes forms, and how your phone battery is just stored physics.

What Is Work?

In physics, work has a very specific meaning:

Work is done when a force causes an object to move in the direction of that force. So, if you push a wall for an hour and it doesn’t move?

Physics says: no work was done. (Sorry.)

The formula is simple:

W = Fd(cos(θ))

Where:

• W = work (in joules)
• F = force
• d = distance moved
• θ = angle between the force and motion direction

If the force and motion are in the same direction, cos(θ) = 1.

If they’re at 90°, like carrying a bag straight up while walking horizontally, physics says: no work again.

What Is Energy?

Energy is the ability to do work. That’s it. It’s like potential, or the capacity to cause change, movement, heat, or action.

There are many types of energy, but two of the most important in physics are:

1. Kinetic Energy (KE)

 – energy of motion

KE = (1/2)mv²

If something is moving, it has kinetic energy. The faster and heavier it is, the more energy it has.

2. Potential Energy (PE)

 – stored energy due to position

PE = mgh

Height = potential. The higher an object is, the more energy it has stored, which will turn into motion when it falls.

The Work-Energy Theorem

This is a big one:

The net work done on an object equals its change in kinetic energy.

That means:

• If work is done on an object, it speeds up.
• If work is done by an object (like stopping), energy is transferred out.

Work causes energy to change.

What About Power?

Power is how fast work is done. It’s energy spent per second.

P = W/t

The unit is the watt (W).

1 watt = 1 joule per second.

A 1000-watt microwave is transferring 1000 joules of energy every second to your frozen burrito. Powerful stuff.

Real-World Energy Examples

• Lifting weights → You’re doing work against gravity.
• Rollercoasters → Convert potential energy (going up) into kinetic energy (coming down).
• Fuel in cars → Chemical energy becomes motion and heat.
• Food → Your body burns it for kinetic and thermal energy (and brain power).

Everything you do, touch, or power is part of an energy exchange.

Conservation of Energy

One of the most important rules in all of science:

Energy cannot be created or destroyed. It only changes form. We call this the Law of Conservation of Energy.

So, when a ball falls, its gravitational potential energy becomes kinetic. When you brake a car, kinetic energy turns into heat. The total amount stays the same—it just swaps costumes.

Why This Matters

Energy ties together every action, every machine, and every biological function. You can’t see energy directly, but you feel its effects all day long.

If you understand how work, energy, and power relate, you can:

• Design efficient machines
• Understand how your body burns calories
• Figure out why your laptop overheats
• Optimize anything that uses fuel, motion, or electricity

Once you understand this, we can get into the fun stuff.