What Sinks
Floating and Sinking: What Sinks
What Sinks
What Sinks
What you'll learn
- An object that goes down and settles at the bottom of water is said to sink.
- A stone sinks in water because it is denser than water.
- A solid iron nail or an iron key sinks because iron is much denser than water.
- A coin sinks in a bucket of water because metal is denser than water.
- Objects that are heavy for their size, with no trapped air, usually sink.
Key concepts
Level 1 - Core idea
Verbal: Objects that are denser than water — heavy for their size and without trapped air — go down and settle at the bottom. This is called sinking.
Symbolic: denser than water -> sinks; no trapped air + heavy for size -> sinks
Visual: Drop a stone and an iron key into a glass of water — both sink straight to the bottom because they are denser than water.
Level 2 - Going deeper
Notice where you see this idea at home, at school, and in your neighbourhood — connecting the concept to daily life makes it easier to remember and use.
Level 3 - NCERT anchor
NCERT EVS Looking Around 4 — simple household experiments of dropping coins, keys, and stones into water show which objects sink.
Worked example
You drop a small stone into a glass of water. What happens and why?
Step 1 - The stone is dense and heavy for its size.
Step 2 - It is denser than the water around it.
Step 3 - Being denser means it cannot stay on the surface.
Answer: The stone sinks to the bottom of the glass.
An iron key is placed in a bowl of water. Does it float or sink?
Step 1 - Iron is much denser than water.
Step 2 - The key has no trapped air to make it lighter.
Step 3 - Being solid and dense, it cannot stay on top.
Answer: The iron key sinks to the bottom of the bowl.
Common mistakes
| Mistake | Why it happens | Fix |
|---|---|---|
| All metal objects always sink | Forgetting that shape can change the outcome | Solid metal objects usually sink, but a hollow, well-shaped metal boat can float |
| Sinking only happens to very big objects | Linking sinking only to large size | Even a small coin sinks because it is dense, regardless of its small size |
| Heavy objects float better than light ones | Reversing the density idea | Heavier, denser objects like stones are more likely to sink, not float |
| Sinking means the object disappears | Misunderstanding what sinking means | Sinking simply means the object settles at the bottom; it is still there |
Quick check
- What does it mean when an object sinks in water?
- Why does a stone sink in water?
- Why does a solid iron nail sink in water?
- Name one small metal object that sinks in a bucket of water.
- Stretch: If a solid iron block sinks, how can a big iron ship still float on the sea?
Revision tip: Ask yourself: is this object heavy for its size compared to water, with no trapped air?
Open the Practice tab for graded questions on What Sinks.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Worked example
- Common mistakes
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