🔬 ScienceLevel 1Lesson 22
← Back🔒 PDF with full access

Experiment — Sink or Float?

Lesson preview: the Mini Lesson and Vocabulary are open to everyone. Guided practice, exercises, the parent checklist and the printable PDF worksheet come with full access (free 7-day trial or membership).

Learning Objectives

  • 1Predict whether everyday objects will sink or float
  • 2Sort objects correctly as sink or float
  • 3Explain that objects float when they are less dense than water — and that size alone does not decide the answer
📘

Mini Lesson

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, marble, metal spoon, nail, key, glass marble.
  • Tricky: a piece of aluminum foil sinks when screwed up into a ball, but floats when shaped into a boat — the shape changes how much water it displaces.
Water container with floating and sinking objectsA clear container of water with a wooden block, cork, and plastic bottle floating at the surface, and a rock, coin, and key resting on the bottom.Float vs Sinkwoodcorkbottlerockcoinkey↑ float↓ sink
Wood, cork, and sealed bottles float — rock, coin, and key sink.
Results table — sink or floatA two-column results table listing six test objects — cork, apple, plastic bottle, rock, coin, and key — and whether each one sinks or floats.Results TableItemSink or Float?corkfloatapplefloatsealed bottlefloatrocksinkcoinsinkPredict first, then test, then record your result.
Record your prediction and your result side by side.
💡

Ask yourself: "Is this object packed tightly with heavy material, or does it have air or light material inside? That tells you if it sinks or floats."

Vocabulary
Sink
To go down to the bottom of the watere.g. A coin will sink in a glass of water.
Float
To stay on top of the watere.g. A wooden stick floats on water.
Density
How tightly packed a material ise.g. Metal has more density than wood.
Predict
To say what you think will happen before you test ite.g. I predict the cork will float.
Experiment
A test we do to learn somethinge.g. Our experiment was sink or float.
Free · 7 days · No credit card

Unlock the full HSEA system for 7 days.

Add your first kid profile and your 7 days start: every lesson in every grade, saved progress for each child. Nothing to set up, no card required, nothing to cancel.

  • ✓ All 1,680 lessons, Grades 1–6, every subject
  • ✓ Profiles + saved progress for every kid
  • ✓ Printable lessons with answer key
Start your 7-day free trial →
Already convinced? See full membership plans →
← Lesson 21: Safe Uses of MaterialsLesson 23: Classifying Objects by Properties →