What happens and why
A law says what. A theory says why.
The smell of cooking
Cooking smells spread from the kitchen to the whole house. That is what happens.
What would a scientist ask next?
What this lesson covers
The idea
A theory goes a step beyond a law and explains why observed patterns occur; it is not a guess or untested idea but an explanation based on evidence, careful testing and critical examination.
The smell of cooking
Cooking smells spread from the kitchen to the whole house. That is what happens.
What would a scientist ask next?
- What colour is the smell?
- Why does the smell spread?
- Who is cooking?
Sort: what or why?
Each card is either what happens or why it happens. Sort them.
A theory explains
A theory goes a step further than a law and explains why patterns occur. A theory is not a guess or an untested idea. It is an explanation based on evidence, careful testing and critical examination.
The atomic theory explains how molecules are formed. Theories can be improved when new evidence arrives, but they are never just guesses.
- Law (pattern) | Theory (explanation)
- Question it answers | What happens? | Why does it happen?
- Example | Smells spread in a room | Particles keep moving, so they spread
- Example | Water: 2 hydrogen to 1 oxygen | Atomic theory: atoms join in fixed numbers
Notes
A theory goes a step beyond a law: it explains why patterns occur. It is not a guess. It rests on evidence, careful testing and critical examination.
- Law: what happens | Theory: why it happens
- Ice melts when heated | Heat makes particles move faster
- Smells spread in a room | Gas particles keep moving
- Water: 2 H to 1 O atoms | Atoms join in fixed numbers
Check yourself
In science, a theory is…
Which sentence is a theory (a why)?
Ravi says, “Atomic theory is just a theory, so it could be anything.” What is wrong with this?
The atomic theory is used to explain…
- a guess nobody has tested. That is the everyday meaning of “theory”. In science it is much stronger.
- an explanation based on evidence and careful testing — correct. Yes. It has been tested and examined critically.
- a law that has been proved wrong. No. A theory explains why patterns occur.
- Water boils at a fixed temperature at sea level. That says what happens.
- Particles of a liquid gain energy and escape as vapour — correct. Yes. This gives a reason for boiling.
- Boiling water makes bubbles. That says what you see.
- Nothing is wrong. In science, a theory is much more than a guess.
- In science a theory is backed by evidence, testing and examination — correct. Yes. It is far stronger than an everyday guess.
- Theories are never tested. Theories are tested again and again.
- How fast a bus can brake. That is about motion, not atoms.
- How molecules are formed — correct. Yes. Atoms join in fixed ways to form molecules.
- Why a ball bounces on a wall. That is about forces, not about how atoms join.