Physics is the study of how everything in the universe works, from the smallest particles to the largest galaxies. It's about understanding the basic rules that govern matter, energy, space, and time. But how do we figure out these rules? We don't just guess. Physicists use a powerful, systematic process to ask questions and find reliable answers. This process is called the scientific method.

The scientific method is a way of learning that emphasizes observation and experimentation. It’s a cycle of thinking and testing that helps us build a clear picture of reality, piece by piece.

It starts with an observation. You notice something and wonder why it happens. Isaac Newton supposedly saw an apple fall from a tree and wondered why it fell straight down, not sideways or up.

Next, you form a hypothesis, which is an educated guess that tries to explain your observation. Newton’s hypothesis was that an invisible force pulls objects toward the center of the Earth.

Then comes the experiment. You design a test to see if your hypothesis is correct. This is the most important part. An idea is only useful in physics if it can be tested. To test the idea of a downward force, you could drop objects of different sizes and weights to see if they all behave the same way.

After the experiment, you analyze the results. What did your measurements tell you? Do they support your hypothesis? If they do, great! If not, you revise your hypothesis and test again. This cycle continues until the hypothesis consistently matches the experimental results. When an explanation has survived countless tests and is widely accepted, it graduates to a theory, like the theory of gravity.

Experiments require measurement. To measure something, you need units. Imagine trying to bake a cake with a recipe that just said to add "some" flour and "a little" sugar. It wouldn't work very well. Science needs specific, standardized units so that researchers around the world can understand and replicate each other's work.

In physics, we use the International System of Units, or SI units. This system provides a global standard for measurement. Here are the three fundamental units you'll use constantly in mechanics:

Nearly every other unit in physics is derived from these basic building blocks. For example, speed is measured in meters per second (m/s). Using a shared system of units is crucial. It ensures that when one physicist in Japan talks about a kilogram, a physicist in Canada knows exactly what they mean.

When you perform an experiment, you aim to get good measurements. But what makes a measurement "good"? This brings up two critical concepts: accuracy and precision.

If a baker's scale says a bag of sugar weighs 1.01 kg, and the bag's true weight is 1.00 kg, the measurement is very accurate.

If the baker weighs the same bag of sugar three times and gets 1.50 kg, 1.51 kg, and 1.50 kg, the measurements are very precise. They are all close to each other. However, they are not accurate, since the true value is 1.00 kg. This suggests a problem with the scale itself, not the baker's technique.

In physics, the goal is always to be both accurate and precise. Good experimental technique helps improve precision, while carefully calibrated instruments help improve accuracy. Understanding this difference is the first step toward thinking like an experimental physicist.

These core ideas—the scientific method, standard units, and the pursuit of accuracy and precision—form the foundation of all physics. They are the tools we use to explore and explain the world in a clear and testable way.