Mechanics is the part of physics that explains how and why things move. It’s the foundation for understanding everything from a thrown baseball to the orbit of a planet.

To keep things simple, we can split mechanics into two main areas. The first is kinematics, which is the language we use to describe motion. The second is dynamics, which explains the causes of that motion, namely forces.

Before we can understand why things move, we need a clear way to talk about their movement. That's where kinematics comes in. It gives us the tools to describe motion precisely, using three key ideas: displacement, velocity, and acceleration.

Displacement isn't the same as the total distance traveled. In the example above, you walked a total distance of 13 meters, but your final position is only 7 meters away from where you started.

Because velocity includes direction, you can change your velocity without changing your speed. A car turning a corner at a constant 30 miles per hour is changing its velocity because its direction is changing.

Now that we can describe motion, we can ask why it happens. The answer is dynamics, and the core principles were laid out by Isaac Newton over 300 years ago. These are known as Newton's Laws of Motion.

This law introduces the idea of inertia, an object's resistance to changes in its state of motion. The more mass an object has, the more inertia it has. It’s why it’s harder to push a car than a bicycle.

This is the most famous of the three laws and is often summarized by a simple equation.

In simple terms, if you push something, it will accelerate. If you push it harder, it will accelerate more. If it’s heavier (has more mass), it will accelerate less.

This means that forces always come in pairs. When you push on a wall, the wall pushes back on you with an equal amount of force. When a rocket expels gas downwards, the gas pushes the rocket upwards. This simple principle explains how so many things in our world work.

Forces and motion are closely linked to two other crucial concepts in mechanics: energy and momentum. These are what we call conserved quantities, which means the total amount of them in a closed system never changes. They just move around or change form.

Work and energy are two sides of the same coin. The work-energy theorem states that the total work done on an object equals the change in its kinetic energy, which is the energy of motion. In other words, doing work on something changes how fast it's moving.

Another fundamental idea is the conservation of energy: energy cannot be created or destroyed, only converted from one form to another, like from potential energy (stored energy) to kinetic energy.

Like energy, momentum is also conserved. The law of conservation of momentum states that the total momentum of a closed system remains constant. This is the key principle behind understanding collisions. When two pool balls collide, the total momentum of both balls before the collision is the same as the total momentum after. Momentum is simply transferred from one ball to the other.

Time to check your understanding of these core concepts.

These building blocks of kinematics, dynamics, energy, and momentum form the basis of all mechanics. Mastering them opens the door to understanding a vast range of physical phenomena.