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Physics · Chapter 1: Introduction to Physics
What is Physics?
Physics is the branch of science that studies matter, energy and the interaction between them. Learn the definition, everyday questions physics answers and how physicists work.
Key termRememberExampleWatch out
01Concept
Physics is the branch of science that studies matter, energy and the interaction between them. The word comes from the Greek word physis, which means nature.
- Matter is anything that has mass and takes up space. A book, water and the air in a football are all matter.
- Energy is the ability to do work. The heat from a gas stove, the light from a bulb and the movement of a rickshaw are all forms of energy.
Questions physics can answer
Physics starts with simple questions about things we see every day:
| Question | The physics behind it |
|---|---|
| Why does a ball you throw up always come back down? | Gravity pulls it towards the Earth. |
| Why does a pencil in a glass of water look bent? | Light changes direction when it enters water. This is refraction. |
| Why do you lean forward when a bus stops suddenly? | Your body tends to keep moving. This is inertia. |
| How does your voice reach someone on a mobile phone? | The phone sends it as electromagnetic waves. |
| Why do we hear thunder after we see lightning? | Light travels much faster than sound. |
From the smallest to the largest
Physics works at every size. The same laws apply to a tiny atom and to a huge galaxy. The diagram shows the sizes physicists study, written in powers of ten. Each step of 10¹ means ten times bigger.
How physicists work
Physics is a quantitative science. This means it depends on measuring things and using numbers. A physicist usually works in these steps:
- Observe something carefully. A pendulum swings back and forth.
- Measure it, with proper units. Time 10 swings with a stopwatch.
- Suggest an explanation (a hypothesis). "A longer string makes each swing take longer."
- Test it with experiments, changing one thing at a time.
- If the results agree again and again, the idea becomes a law or theory.
Physics is also called a basic (fundamental) science, because other sciences use its ideas. Chemistry uses the physics of atoms, biology uses it to explain how the eye and ear work, and geography uses it to explain earthquakes and weather.
02Real World Examples
Your electricity bill
The bill measures the energy your home used, in kilowatt-hours (kWh): one "unit" on the bill is 1 kWh. Measuring energy is physics.
Karachi's sea breeze
On summer afternoons, land heats up faster than the sea. Warm air over the land rises, and cooler air from the sea moves in to take its place. This is convection.
Swing bowling
When one side of a cricket ball is kept shiny and the other side is rough, air flows differently over the two sides. The difference pushes the ball sideways, so it swings.
A pressure cooker
Steam trapped inside raises the pressure, so water boils above 100 °C and food cooks faster.
03Practice Questions
Try to answer in your own words first, then open the model answer.
Short questions
Q1.Define physics. Where does the word come from?Show answer
Answer
Physics is the branch of science that deals with the study of matter, energy and the interaction between them.
The word comes from the Greek word physis, meaning nature.
Q2.What are matter and energy? Give one example of each.Show answer
Answer
- Matter: anything that has mass and occupies space. Example: water.
- Energy: the ability to do work. Example: heat from a stove.
Q3.Why is physics called a quantitative science?Show answer
Answer
Because physics depends on measurement and numbers. Physicists measure quantities such as length, mass and time, and use the results to find laws.
Q4.Why is physics called a basic (fundamental) science?Show answer
Answer
Because other sciences are built on its ideas. For example, chemistry uses the physics of atoms, biology uses it to explain how the eye works, and geography uses it to explain earthquakes.
Long questions
Q5.Describe the steps physicists follow when they study something new. Use an example.Show answer
Answer
- Observation: notice something. A pendulum swings back and forth.
- Measurement: measure it with units. Time 10 swings with a stopwatch.
- Hypothesis: suggest an explanation. A longer string gives a slower swing.
- Experiment: test the idea, changing one thing at a time. Change only the string length.
- Law or theory: if the results agree every time, the idea is accepted as a law or theory.