Experiment — Sink or Float?

Drop a coin and a wooden stick into water. The coin sinks to the bottom while the stick bobs at the surface. Why? Scientists discovered it all comes down to something called density.

What is density?

• Density is how much material is packed into a space.
• A heavy metal coin packs a lot of material into a small space — it is denser than water so it sinks.
• A wooden stick has air pockets in it — it is less dense than water so it floats.
• Example: A large beach ball floats — even though it is big — because it is mostly air.

The rule

• If an object is denser than water → it sinks.
• If an object is less dense than water → it floats.
• Size does NOT decide it alone — a tiny pebble sinks, but a huge ship floats because the ship's hull traps air and makes it less dense overall.

Common examples

• Floats: cork, wood, foam, plastic bottle (sealed), apple, leaf, ice.
• Sinks: coin, pebble, glass marble, metal spoon, nail, key.
• Tricky: a piece of aluminum foil sinks when squeezed tightly into a ball, but floats when shaped into a boat — the shape changes how much water it pushes aside.