Sink or Float? Understanding Density

About This Resource

A free Grade 6 science worksheet pack on density: mass and volume, the formula density = mass ÷ volume, units such as g/cm³, why objects sink or float in water, density columns with liquids and everyday examples such as ships, ice and hot air balloons. Includes a timed lesson plan, worksheet, editable Word version and answer key.

Overview

Students learn that density tells us how much mass is packed into a certain volume. They calculate density with the formula density = mass ÷ volume, compare objects to the density of water (1 g/cm³) to predict sinking and floating, read about a layered liquid density column, and explain everyday puzzles such as why ice floats, why a steel ship floats and why hot air balloons rise.

Resource Details

Subject: Science
Topic: Density
Category: Materials & Matter
File Type: PDF
File Size: 254.8 KB
Published: 31 Oct 2026
Downloads: 0

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Grade 6 (ages 11–12) 45 minutes Physical science calculating predicting reading explaining

Student Task

Drop a grape and a ping-pong ball into water and ask why one sinks and one floats.
Teach the formula, then do activities 1 and 2 together.
Students complete activities 3 to 5; answers are in the answer key.

Classroom Use

Density column: carefully pour honey, dish soap, water and vegetable oil into a clear cup and drop in small objects.
Egg float: an egg sinks in fresh water but floats when lots of salt is stirred in.
Clay boats: a ball of clay sinks, but the same clay shaped into a boat floats.

Differentiation

Support: use a formula triangle and whole-number calculations. Challenge: rearrange the formula to find mass or volume and explain why salt water is denser than fresh water.

Answer Key & Assessment

Activities 1 to 4 check density ideas and calculations (answer key included). Activity 5 checks explanations.

Learning Objectives

Define density and explain how it depends on mass and volume.
Calculate density using density = mass ÷ volume.
Use density to predict and explain whether objects sink or float.

Teacher Tips

Use the crowded room idea: the same room with more people packed in is denser. Density is about how tightly mass is packed, not just how heavy something is.

What's Included

6-page printable PDF lesson pack: teacher lesson plan with timings, materials and differentiation
Key vocabulary list (4 words with meanings and examples)
Student worksheet (5 activities)
Editable Word version of the worksheet
Complete answer key (also as a separate PDF)