LF-26 · TEACHER LESSON PLAN

Sink or float lab

Test how density, shape and trapped air affect floating

PhysicsGrades 2–620–25 minHazard low; spills and small objectsNGSS MS-PS1-1

01 //

Driving question

START THE LESSON WITH THISHow do average density, shape and trapped air help explain an object's settled position in water?

02 //

Learning objectives

Students predict whether each safe everyday object will sink or float before testing it in the same water.
Students classify the actual settled position separately from the prediction and distinguish floating, sinking, suspension and change over time.
Students explain how buoyant force, average density, shape and trapped air help explain the observation, while noting that the test alone does not measure density.

03 //

Standards

Dimension	Alignment
Performance expectation	MS-PS1-1Develop models to describe the atomic composition of simple molecules and extended structures. (Partial alignment: this is the performance expectation the lab lists, but the activity investigates a physical property of matter (object density compared with water) rather than building atomic models.)
Practices	SEP 3Plan and carry out investigations.
Core idea	PS1.AEach pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it.
Crosscutting	Cause and effectCause and effect relationships are routinely identified, tested, and used to explain change.

Standards text paraphrased from nextgenscience.org. Alignment is partial; this hands-on activity does not cover every part of the performance expectation. CCC wording not independently verified.

03A //

State standards crosswalk

Use the row as a planning crosswalk, then confirm local district pacing and grade placement. “Partial” labels describe a skill connection, not full mastery of the complete standard.

State	Verified standard	How this lesson aligns	Official source
California	CA NGSS 2-PS1-1	Partial. Students investigate and classify objects by an observed sink-or-float property, while the lesson's optional density calculations extend beyond the standard's listed observable-property examples.	Open standard ↗
Texas	Science.5.6(A)	Partial. Testing and comparing sink-or-float behavior connects directly to relative density, but the lesson does not test the full list of physical properties named by this grade-five expectation.	Open standard ↗
Florida	SC.1.P.8.1	Direct activity connection. The benchmark explicitly includes whether objects sink or float among observable properties; the optional mass-volume density calculation extends beyond the benchmark wording.	Open standard ↗
New York	2-PS1-1	Partial. Students plan a simple water test and classify materials by an observable result; sink-or-float is not among the standard's example properties, and density is not developed there.	Open standard ↗
Pennsylvania	3.2.2.A	Partial. The class conducts an investigation and classifies materials by an observed result, but the standard's examples focus on color, texture, hardness, and flexibility rather than density.	Open standard ↗

04 //

Materials and prep timeline

PER GROUP

Stable clear basin with room-temperature water
Large nonporous wooden block, metal spoon, plastic cap, rubber eraser and whole orange
Balance and ruler; graduated cylinder only for suitable nonporous samples
Towel, labels and recording sheet
Tray to contain drips

TEACHER ONLY

Choose large, clean, non-breakable objects without sharp edges; avoid small parts with young children.
Keep the water basin stable and away from electrical equipment; prepare a dry spill area.
Provide one student sheet per student; remind students not to put objects or water in their mouths.

CLASS-SIZE KIT PLANNER

One per-group kit contains every item in the team materials list above. Groups are balanced around the listed 3–4 students target.

Students	Groups	Per-group kits	Student sheets	Suggested group split
20	6	6 complete kits	20 copies	2 groups of 4 and 4 groups of 3
25	7	7 complete kits	25 copies	4 groups of 4 and 3 groups of 3
30	8	8 complete kits	30 copies	6 groups of 4 and 2 groups of 3

0–4 MINPredict and sort

List the five objects, note their shape and visible air spaces, then predict a result and state one reason before testing.

4–12 MINTest one at a time

Lower each object gently into the same basin. Wait for the water to settle and record the result.

12–18 MINUse optional measurements

Only for suitable nonporous samples, measure mass and valid volume, calculate density, and compare with the water; mark the rest not measured.

18–22 MINReview surprises

Compare predictions with actual positions; discuss buoyant force, shape, trapped air and possible surface-tension effects.

22–25 MINExplain and clean

Use density rather than heaviness alone, then dry the surface and return objects.

04A //

Lab figures and data visuals

Reviewed article images support the lesson flow. Use the tables and student sheet to record actual observations; pictured patterns are not target results.

A hand tests a rock in a clear basin while wood and a whole orange float and a metal spoon rests on the bottom. — **Predict, test and observe.**Record the actual settled position separately; examples in the picture are not guaranteed for every sample.

A foil boat carrying metal washers and a wooden block float, while a flat foil sheet and solid metal cube rest on the bottom of a water tub. — **Connect shape with displacement.**Use equal foil mass for the extension; shape and trapped air change the whole object's average density and displacement.

A clear basin and five safe test objects sit beside a blank observation grid and pencil. — **Keep the observation record.**Density calculations are optional and require valid mass and volume measurements.

04B //

Printable shopping list

TEACHER PREP · Sink or float lab

Shopping and staging checklist

Multiply the per-group kit contents by the class-size planner. The teacher section includes teacher-provided materials and setup or safety notes.

PER-GROUP KITS

Stable clear basin with room-temperature water
Large nonporous wooden block, metal spoon, plastic cap, rubber eraser and whole orange
Balance and ruler; graduated cylinder only for suitable nonporous samples
Towel, labels and recording sheet
Tray to contain drips

TEACHER-PROVIDED MATERIALS + SETUP RULES

Choose large, clean, non-breakable objects without sharp edges; avoid small parts with young children.
Keep the water basin stable and away from electrical equipment; prepare a dry spill area.
Provide one student sheet per student; remind students not to put objects or water in their mouths.

QUANTITIES BY CLASS SIZE

Material	Per group kit	20 students	25 students	30 students
Wooden blocks, metal spoons, plastic caps, rubber erasers, and oranges	1 of each	6 of each	7 of each	8 of each
Stable clear basins filled with water	1	6	7	8
Balances, rulers, and graduated cylinders	1 of each	6 of each	7 of each	8 of each
Trays and towels	1 of each	6 of each	7 of each	8 of each
Object labels	5	30	35	40
Student prediction and observation sheets	1 per student	20 copies	25 copies	30 copies

Prepare 6 kits for 20 · 7 kits for 25 · 8 kits for 30 students.

05 //

Lesson flow

Minutes	What happens
0–4	Engage Predict sink or float for a wooden block, metal spoon, plastic bottle cap, rubber eraser and orange with peel. Record reasons before testing.
4–12	Explore Use one stable basin of room-temperature water. Lower each large, safe object gently and record the actual classification after ripples stop.
12–18	Only for suitable samples, measure mass and valid volume, then calculate mass ÷ volume. Mark unsuitable samples not measured.
18–22	Explain Compare predictions with observations. Discuss buoyant force, shape, trapped air and how the same foil can sink flat or float as a boat.
22–25	Evaluate Explain one surprise without using total weight alone; dry drips and keep water away from electrical items.

06 //

Discussion questions

1. Why can a large wooden block float even if it feels heavy?

SAMPLE ANSWERThe upward buoyant force balances the block's weight when it displaces enough water. Its average density may be lower than water even when its total mass is large.

2. What did the prediction column let you compare?

SAMPLE ANSWERIt preserves the initial sink/float classification and reason so students can compare their idea with the result after the water settles.

3. Why might the orange float with its peel?

SAMPLE ANSWERAir pockets in the peel can lower the average density of the whole orange. This is a useful explanation to test with the observed orange, not a guarantee for every fruit.

4. Does the float-or-sink observation measure density?

SAMPLE ANSWERNo. Density requires mass and volume measurements. The observation can be explained with buoyant force and whole-object average density, while shape and trapped air affect displacement.

07 //

Common misconceptions

STUDENTS OFTEN SAY“Heavy things sink and light things float.”

BETTER IDEACompare mass per volume: a large object can be heavy overall and still less dense than water.

STUDENTS OFTEN SAY“Every metal object sinks, regardless of its shape.”

BETTER IDEAA metal sheet can be shaped into a boat; whole-object average density and displaced water depend on shape and trapped air.

STUDENTS OFTEN SAY“A prediction is the same as an observation.”

BETTER IDEAKeep the prediction recorded before testing, then classify the actual result separately.

STUDENTS OFTEN SAY“Anything touching the water surface is less dense than water.”

BETTER IDEASurface tension can support very small objects such as a paper clip; use larger objects to focus on density and buoyancy.

08 //

Differentiation

SUPPORT

Use two large picture cards labeled FLOAT and SINK and let students place each prediction before testing.
Demonstrate lowering one object gently and waiting for ripples to stop before recording.
Offer the frame: “I predicted ___. It actually ___. Its density is ___ than water / not measured.”

EXTEND

Measure mass and volume for a regular block and calculate density in g/mL.
Compare an orange with peel and the same orange peeled as a separate follow-up test.
Test a sealed hollow container and explain why its average density differs from the material its shell is made from.

09 //

Assessment rubric

Criterion	Beginning	Developing	Secure
Prediction	Leaves predictions blank or copies results after testing.	Predicts most objects but omits reasons or labels.	Records a sink/float prediction and a reason for each object before testing.
Classification	Does not record actual results.	Records most actual results but mixes predictions and observations.	Classifies each object from the settled observation and compares it with the prediction.
Density evidence	Explains only by total weight.	Names density but does not relate it to water or measured values.	Uses mass/volume only when both were validly measured and compares with water; marks other samples not measured.
Explanation	Claims object size or material name alone determines the result.	Explains one case but omits shape or trapped air.	Explains a result using average density and recognizes shape or trapped air as a factor.

10 //

Vocabulary

Density – Mass divided by volume; how much mass occupies a given amount of space.
Mass – A measure of the amount of matter in an object.
Volume – The amount of space an object or sample occupies.
Displacement – The amount of water moved aside when an object is submerged.

Classification – Grouping an observation by a stated rule, such as sink or float.
Average density – Total mass divided by the whole object's volume, including sealed air spaces.
Buoyant force – The upward force from water, equal to the weight of the water displaced by a submerged object.
Surface tension – A surface effect that can support some very small objects without showing the usual bulk-density pattern.

11 //

Safety, cleanup and troubleshooting

BEFORE STUDENTS TOUCH ANYTHING

Use large, clean, non-breakable objects with no sharp edges. Avoid small parts around young children, and never put test objects or water in your mouth.
Lower objects gently into a stable basin, keep water away from electrical equipment, and dry spills promptly.

Troubleshooting: If an object is difficult to classify, wait for ripples to stop and check that it is not resting against the basin wall. If water spills, pause testing and dry the floor before walking through the area.