Sink or Float Science Fair Project

90+ Sink or Float Science Fair Project: The Mystery of Buoyancy

Discover the principles of buoyancy with our sink or float science fair project. Engage in hands-on experimentation and learn about density and displacement.

Imagine this: you’re at the edge of a serene pond, contemplating the whimsical ballet of leaves, twigs, and maybe a toy boat, all floating effortlessly on the water’s surface. Ever wondered why some things get to be the stars of this watery show while others remain hidden below?

Well, get ready for a splash of curiosity and a wave of excitement because the “Sink or Float” science fair project is here to unravel these aquatic mysteries!

In this project, we’re going to embark on an exhilarating journey into the world of buoyancy. We’ll dive headfirst into experiments and observations that will help us decode why certain objects gracefully stay afloat, defying gravity’s pull, while others mysteriously vanish beneath the water’s surface. It’s like a backstage pass to Mother Nature’s very own magic show!

So, if you’re ready to become a buoyancy wizard and uncover the secrets of why things sink or swim, grab your goggles and prepare to set sail on this thrilling voyage of scientific exploration!

What is sink and float science experiment?

The “sink and float” science experiment is a simple but engaging investigation aimed at understanding the concept of buoyancy. It involves observing and testing various objects to determine whether they will sink or float when placed in a liquid, typically water.

This experiment is often used in elementary and early science education to introduce students to the basic principles of physics and buoyancy.

Here’s a brief overview of how the sink and float science experiment works:

Materials Needed

  • Various objects with different shapes, sizes, and materials (e.g., coins, wooden blocks, plastic toys, rubber balls, metal objects).
  • A container filled with water (a clear plastic tub or a fish tank works well).
  • A notebook and pen or pencil for recording observations.
  • Safety goggles (optional but recommended for eye protection).


Gather Objects

Collect a variety of objects for testing. It’s essential to choose objects made of different materials and with various densities (some heavy, some light).

Fill the Container

Fill your container with water, leaving enough space at the top to prevent overflow when you add objects.

Predict and Record

Before placing any objects in the water, make predictions about which objects you think will sink and which will float. Record these predictions in your notebook and provide reasons for your hypotheses.

Test the Objects

One by one, carefully place each object into the water, observing what happens. Take note of whether the object sinks to the bottom or floats on the surface.

Record Observations

In your notebook, record the results of each object tested. Be sure to describe what you see, whether it sank or floated, and any other observations you make.

Analyze and Conclude

Review your predictions and compare them to your actual observations. Write a conclusion summarizing your findings. Explain why some objects floated while others sank, using the concept of density (denser objects sink, less dense objects float) to support your explanations.

Optional Display

If this is part of a science fair or school project, create a display board to showcase your experiment, including the objective, materials, procedure, results, and conclusion. You can add visuals like photographs, diagrams, or graphs to enhance your presentation.

The sink and float experiment is a fantastic way to introduce young scientists to the concepts of buoyancy, density, and the scientific method. It encourages critical thinking, observation, and hypothesis testing while providing a hands-on experience with the laws of physics in action.

What is the hypothesis of sink or float?

The hypothesis for a “Sink or Float” experiment typically revolves around predicting how objects will behave in water based on their density. Here’s a straightforward hypothesis:

“I hypothesize that objects with a density greater than that of water will sink when placed in water, while objects with a density less than that of water will float.”

In this hypothesis, you’re stating your educated guess about the relationship between an object’s density and its behavior in water. You’re predicting that denser objects will sink because they are heavier and have more mass packed into a given volume compared to water.

Conversely, less dense objects are predicted to float because they are lighter and have less mass in the same volume compared to water. This is a fundamental principle of buoyancy.

Sink or Float Science Fair Project

Have a close look at sink or float science fair project

Material-Based Categories

Metal vs. Non-Metal

Compare the buoyancy of metal objects (e.g., coins, nails) with non-metal objects (e.g., plastic toys, wooden blocks). Explore how the material affects their sinking or floating behavior.

Wood vs. Plastic

Test the buoyancy of wooden boats and plastic boats of similar sizes and shapes. Investigate whether the material impacts their floating capacity.

Natural vs. Synthetic

Examine the behavior of natural materials like leaves and twigs compared to synthetic materials like plastic foliage when placed in water. Analyze any differences in buoyancy.

Glass vs. Plastic Containers

Fill glass and plastic containers with the same volume of water and observe whether their material affects the buoyancy of objects placed in them.

Cork vs. Clay

Compare the buoyancy of corks and small clay sculptures. Determine how the material density influences their behavior in water.

Metal vs. Plastic Spoons

Investigate whether metal and plastic spoons have different buoyancy characteristics when submerged in water.

Foam vs. Rubber

Test the buoyancy of foam and rubber objects (e.g., foam balls and rubber balls) to see if their material composition affects their ability to float.

Natural Fiber vs. Synthetic Fiber

Explore how objects made of natural fibers (e.g., cotton balls) compare to those made of synthetic fibers (e.g., polyester) in terms of buoyancy.

Paper vs. Cardboard

Test the buoyancy of paper and cardboard shapes (e.g., paper cutouts and cardboard squares) to see how their material composition influences their floating behavior.

Plastic vs. Glass Beads

Compare the buoyancy of plastic beads and glass beads of similar sizes and shapes. Investigate whether the material affects their sinking or floating.

Shape-Based Categories

Shape and Buoyancy

Experiment with various shapes, such as cubes, spheres, and cylinders, made from the same material (e.g., clay). Determine how shape impacts buoyancy.

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Aerodynamic vs. Non-Aerodynamic

Test objects with streamlined shapes (e.g., boat-shaped objects) against irregular shapes (e.g., crumpled paper). Observe which shapes tend to float more easily.

Flat vs. Curved

Compare the buoyancy of flat objects (e.g., cardboard sheets) with curved objects (e.g., plastic bowls). Explore how shape curvature affects their floating or sinking behavior.

Geometric Shapes

Investigate how various geometric shapes, like triangles, rectangles, and circles, made from the same material, behave when placed in water.

Cube vs. Pyramid

Test the buoyancy of cubes and pyramids of the same material (e.g., wooden blocks) and determine how their shapes influence their sinking or floating.

Spiral vs. Straight

Compare objects with spiral shapes (e.g., coiled wire) to objects with straight shapes (e.g., pencils). Analyze their buoyancy characteristics.

Hollow vs. Solid

Examine the buoyancy of objects with different internal structures, such as hollow plastic balls compared to solid plastic balls.

Symmetry vs. Asymmetry

Investigate whether symmetrically shaped objects (e.g., symmetrical paper cutouts) float differently from asymmetrically shaped objects (e.g., random paper scraps).

Star-Shaped vs. Circular

Compare the buoyancy of star-shaped objects (e.g., wooden stars) to circular objects (e.g., wooden discs) and observe how their shapes affect their behavior in water.

Polygonal Shapes

Experiment with objects of various polygonal shapes (e.g., hexagons, octagons) and observe whether their number of sides influences their buoyancy.

Size-Based Categories

Size and Buoyancy

Test objects made from the same material but with different sizes (e.g., small plastic balls and large plastic balls). Explore how size impacts their floating behavior.

Tiny vs. Giant

Investigate whether tiny objects (e.g., tiny pebbles or grains of sand) behave differently from much larger objects (e.g., large stones or rocks) when placed in water.

Microscopic vs. Macroscopic

Explore how the scale of objects, such as microscopic particles (e.g., salt crystals) versus macroscopic items (e.g., wooden blocks), influences their buoyancy.

Miniature vs. Life-Size

Compare the buoyancy of miniature toy boats to life-size model boats. Determine whether size plays a role in their floating capacity.

Small vs. Large Corks

Test corks of different sizes, from small wine corks to large bottle stoppers, and observe how size affects their ability to float.

Tiny vs. Large Leaves

Examine whether tiny leaves from plants like ferns float differently from larger leaves from broad-leafed plants when placed in water.

Tiny vs. Large Plastic Capsules

Investigate the buoyancy of tiny plastic capsules (e.g., medicine capsules) compared to larger ones (e.g., vending machine capsules).

Small vs. Big Bubbles

Experiment with small soap bubbles and large soap bubbles to see how size influences their buoyancy in the air and water.

Mini vs. Mega Coins

Test the buoyancy of small coins (e.g., pennies) compared to larger coins (e.g., silver dollars) to observe how size impacts their behavior in water.

Small vs. Large Balloons

Inflate small balloons and large balloons with helium and observe how size affects their ability to float in the air (helium) and water.

Density-Based Categories

Density and Buoyancy

Investigate how the density of an object’s material influences whether it sinks or floats in water. Test objects with varying densities (e.g., wooden blocks, plastic blocks).

Homogeneous vs. Heterogeneous

Compare the buoyancy of objects with materials that have a uniform density (e.g., solid plastic blocks) against those with non-uniform density (e.g., hollow plastic balls filled with air).

Density Gradient

Create a density gradient in a container by dissolving different amounts of salt in water to form layers of varying salinity. Test how objects behave as they move through these layers.

Solid vs. Hollow Shapes

Test the buoyancy of solid shapes (e.g., solid plastic spheres) against hollow shapes (e.g., plastic spheres with a hollow interior).

Layered Density

Explore how the placement of objects with different densities within a container of water (e.g., layers of oil, water, and syrup) affects their buoyancy.

Water Temperature and Density

Investigate how water temperature affects water density and, consequently, the buoyancy of objects placed in warm and cold water.

Material Mixtures

Create objects with materials of varying densities (e.g., clay with embedded metal weights). Test these composite objects to see how the combination of materials influences buoyancy.

Variable Density Blocks

Make blocks with varying densities by adding different amounts of materials (e.g., sand, beads, clay) to them. Observe how these variable density blocks behave in water.

Composite vs. Pure Materials

Compare the buoyancy of objects made of pure materials (e.g., solid metal cubes) with objects made of composite materials (e.g., metal cubes with a plastic coating).

Density and Air Pockets

Investigate how the presence of air pockets within objects affects their buoyancy. Test objects with varying levels of trapped air.

Temperature-Based Categories

Temperature and Buoyancy

Explore how water temperature affects the buoyancy of objects. Test objects in warm water and cold water to observe any differences in their behavior.

Hot vs. Cold Water

Compare the buoyancy of objects in hot water (near boiling) with that in ice-cold water (near freezing) to understand how extreme temperature changes affect buoyancy.

Warm Water vs. Room Temperature

Investigate whether objects behave differently when placed in water that is slightly warmer than room temperature versus water at room temperature.

Temperature Gradient

Create a temperature gradient in a container of water by heating one end and cooling the other. Test objects to see how they move through the temperature layers and whether it impacts their buoyancy.

Thermal Expansion

Study the concept of thermal expansion by observing how the buoyancy of objects changes as they heat up and expand in warm water.

Water and Ice

Experiment with the buoyancy of objects in ice-cold water and then in water at room temperature to compare their behavior when transitioning between states.

Hot Water vs. Cold Water Baths

Test objects that have been placed in hot water baths and cold water baths before observing their buoyancy in room temperature water.

Thermal Dynamics

Investigate the relationship between temperature and density by measuring the temperature of water and examining how it correlates with the buoyancy of objects.

Heated vs. Chilled Objects

Heat some objects and chill others before placing them in room-temperature water. Observe how the initial temperature of the objects affects their buoyancy.

Thermal Time Delay

Analyze whether objects with different thermal properties (e.g., metal vs. wood) exhibit differences in buoyancy when placed in water, considering the time delay in temperature changes.

Salinity-Based Categories

Saltwater vs. Freshwater

Compare the buoyancy of objects in saltwater to that in freshwater. Explore how salinity impacts sinking and floating behaviors.

Salinity Gradient

Create a gradient of salinity in a container by adding different amounts of salt to water, creating layers of varying salinity. Test how objects move through these layers.

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Changing Salinity Over Time

Experiment with objects in water where the salinity is gradually increased or decreased over time. Observe how these changing salinity conditions affect buoyancy.

Ocean vs. Lake Water

Investigate whether objects behave differently in water with a salt content similar to ocean water versus water from a freshwater lake.

Brackish Water vs. Tap Water

Compare the buoyancy of objects in brackish water (a mix of saltwater and freshwater) to that in tap water. Analyze how the combination affects buoyancy.

Saline vs. Non-Saline Solutions

Create solutions with varying salinity (e.g., saline solution, sugar water) and test how objects respond when placed in these different solutions.

Changing Salinity Gradients

Investigate how objects move through water with changing salinity gradients and whether this movement correlates with their buoyancy.

Ocean Layers

Simulate the layers of ocean water with varying salinity (e.g., surface layer, thermocline) and test objects to see how they behave as they pass through these layers.

Salinity and Dissolved Substances

Examine whether the presence of dissolved substances in water (e.g., salt and sugar) affects buoyancy differently in saltwater compared to freshwater.

Salinity and Biodiversity

Explore the impact of salinity on the buoyancy of objects in water inhabited by various aquatic organisms. Investigate whether different species have varying buoyancy responses to changing salinity.

Biological Categories

Plant vs. Animal Materials

Test the buoyancy of objects made from plant-based materials (e.g., leaves, twigs) against those made from animal-based materials (e.g., feathers, bones). Investigate whether biological origin affects buoyancy.

Different Types of Feathers

Experiment with feathers from different bird species (e.g., duck feathers, owl feathers) and observe how their unique structures influence their floating or sinking behavior.

Leaves from Various Plants

Collect leaves from different types of plants (e.g., deciduous, evergreen) and analyze whether the characteristics of these leaves affect their buoyancy.

Natural vs. Synthetic Materials

Compare the buoyancy of natural materials (e.g., pine cones, seashells) with synthetic materials (e.g., plastic imitations) to see if their origin influences how they behave in water.

Bones vs. Stems

Investigate whether objects resembling bones (e.g., chicken bones) and objects resembling plant stems (e.g., bamboo sticks) have different buoyancy properties.

Fruits vs. Plastic Fruit Models

Test the buoyancy of real fruits (e.g., apples, oranges) against artificial plastic fruit models. Analyze whether the differences in material affect their behavior in water.

Pet Hair vs. Synthetic Fur

Compare the buoyancy of pet hair (e.g., dog or cat fur) with synthetic fur samples. Explore whether the source of the fur influences buoyancy.

Different Types of Shells

Collect shells from various marine creatures (e.g., snail shells, clam shells) and assess whether their shapes and sizes affect buoyancy.

Fish Scales vs. Plastic Fish Models

Experiment with fish scales versus plastic fish models to see if natural fish scales exhibit distinct buoyancy properties.

Plant Roots vs. Synthetic Roots

Investigate whether the behavior of plant roots (e.g., carrot roots) differs from that of synthetic roots (e.g., plastic plant roots) when submerged in water.

Historical Categories

Historical Buoyancy Reenactment

Recreate and explain historical events involving sinking and floating, such as the sinking of the Titanic. Explore the principles of buoyancy that played a role in these events.

Archimedes’ Principle

Investigate and demonstrate Archimedes’ principle, which explains buoyancy, by reenacting the famous “Eureka!” moment when Archimedes discovered the principle in his bath.

Historical Naval Warfare

Explore how the principles of buoyancy and ship design affected historical naval warfare. Analyze battles or naval innovations from different time periods.

Historical Shipwrecks

Investigate famous shipwrecks (e.g., the Mary Rose, the Vasa) and discuss how buoyancy played a role in their sinking and preservation.

Floating Technology Evolution

Trace the evolution of floating technology, from ancient rafts to modern ships, and explain how advancements in design and materials have improved buoyancy.

Historical Submarines

Explore the history of submarines and how their buoyancy control mechanisms have evolved over time, enabling them to submerge and resurface safely.

Historical Aircraft

Investigate historical aircraft, such as hot air balloons and airships, and explain how their buoyant gases allowed them to fly.

Ancient Aquatic Architecture

Examine historical structures like aqueducts, bridges, and water mills that relied on principles of buoyancy and water flow for functionality.

Archaeological Buoyancy

Analyze archaeological discoveries that involve submerged artifacts or ancient sunken cities, focusing on the role of buoyancy in their preservation and recovery.

Historical Naval Innovators

Explore the contributions of historical figures like Leonardo da Vinci and Robert Fulton to naval innovation and their impact on buoyancy-related technologies.

Environmental Impact Categories

Floating Debris and Pollution

Investigate the environmental impact of floating and sinking debris in water bodies, highlighting the importance of proper waste disposal and its consequences on aquatic ecosystems.

Microplastics and Buoyancy

Examine how microplastic particles in water affect buoyancy and discuss the environmental implications of microplastic pollution in aquatic environments.

Oil Spills and Cleanup Methods

Explore the buoyancy of oil spills on water surfaces and evaluate different cleanup methods, including techniques that rely on buoyant materials.

Floating Wetlands

Investigate the use of artificial floating wetlands to improve water quality and habitat restoration in polluted water bodies.

Floating Solar Panels

Analyze the use of floating solar panels on bodies of water and discuss their impact on renewable energy generation and water ecosystems.

Buoyancy in Water Treatment

Explore how buoyancy-based water treatment technologies, such as flotation, are used to remove pollutants and contaminants from wastewater.

Floating Trash Collectors

Investigate the effectiveness of floating trash collection devices in removing debris and plastics from rivers and other water bodies.

Aquatic Invasive Species Control

Examine the use of buoyancy-based barriers and traps to control invasive aquatic species and protect native ecosystems.

Buoyant Habitat Restoration

Discuss projects that use buoyant structures to create habitats for wildlife in areas affected by habitat loss or degradation.

Buoyancy and Climate Change: Explore the impact of rising sea levels due to climate change and discuss how buoyancy is a critical factor in adaptation strategies and the design of resilient coastal infrastructure.

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What items do you use for sink or float experiment?

For a “Sink or Float” experiment, you can use a variety of objects with different shapes, sizes, and materials to observe their behavior in water. Here’s a list of common items you can use:

  • Coins: Different denominations of coins made from various metals like copper, nickel, and zinc.
  • Wooden Blocks: Small wooden blocks or cubes.
  • Plastic Toys: Small plastic toys or figurines.
  • Rubber Balls: Rubber balls of different sizes.
  • Metal Objects: Objects made of metal like paperclips, screws, or small aluminum foil balls.
  • Corks: Corks from bottles.
  • Plastic Bottles: Empty plastic bottles, which can be partially filled with water or sealed with air inside.
  • Sponges: Dry sponges and wet sponges to observe the difference.
  • Feathers: Feathers from different birds.
  • Marbles: Glass or plastic marbles.
  • Lego Bricks: Lego building bricks of various shapes and sizes.
  • Egg: A fresh egg (to compare with other objects).
  • Styrofoam: Small pieces of styrofoam.
  • Aluminum Foil: Small pieces of aluminum foil.
  • Plastic Cups: Upside-down plastic cups to see if they float or sink.
  • Pencil: A pencil with an eraser on top.
  • Paper: Crumpled paper or a folded paper boat.
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These items are typically chosen because they represent a range of materials and densities. This diversity allows you to observe how different materials and densities affect whether an object sinks or floats in water. Before conducting the experiment, make a list of the items you plan to test, and you can also make predictions about which ones you think will sink or float based on their properties.

What are 10 examples of float and sink?


  • Rubber Duck: A classic example of an object that floats in water, thanks to its buoyant design.
  • Plastic Bottle (empty): An empty plastic bottle usually floats because it contains air, which is less dense than water.
  • Inflatable Beach Ball: Inflatable objects filled with air tend to float due to the low density of air compared to water.
  • Cork: Corks from wine bottles are known for their buoyancy and typically float in water.
  • Leaf: Leaves from trees often float on the surface of water bodies due to their low density.


  • Stone: Most stones and rocks are denser than water, causing them to sink when placed in water.
  • Iron Nail: A nail made of iron is much denser than water, so it sinks when placed in it.
  • Penny (coin): Pennies are denser than water due to their metallic composition, so they sink.
  • Metal Spoon: Metal objects like spoons are generally denser than water and sink when submerged.
  • Paper Towel (soaked): While a dry paper towel may float when soaked with water, it becomes denser and sinks.

Remember that the behavior of an object in water depends on its density relative to the density of water. Objects less dense than water tend to float, while those denser than water typically sink. The “Sink or Float” experiment helps illustrate this concept and allows you to observe it with various objects.


Our voyage through the “Sink or Float” experiment has been nothing short of an exhilarating adventure! We embarked on this scientific journey with questions aplenty and a thirst for knowledge that couldn’t be quenched. Our mission? To unravel the age-old mystery of buoyancy.

Our trusty hypothesis, which confidently predicted that denser objects would take the plunge, while lighter ones would gracefully surf the water’s surface, guided us through this exciting exploration. Along the way, we encountered an eclectic mix of objects, each with its own story to tell.

In the realm of materials, we uncovered the secret language of stuff. Metals like coins and nails whispered tales of weightiness as they disappeared into the depths. Meanwhile, wood and plastic objects flaunted their buoyant prowess by flaunting their staying power afloat. Mother Nature herself had something to say in this conversation, as leaves and sticks showcased their mastery of the art of floating.

Shapes, oh shapes! They danced before our eyes, revealing the choreography of physics. Smooth, aerodynamic forms, like our trusty toy boats, took center stage with their graceful floating performances, while the unruly and irregular shapes tried valiantly but often found themselves in the watery depths.

Size became our close companion, showing us that small things can sometimes outshine their larger counterparts. Who would have thought that tiny grains of sand could defy gravity while mighty pebbles surrendered to the underwater world?

Density, our scientific sidekick, held the key to many a mystery. We saw how the uniformity of materials could spell the difference between floating and sinking. Hollow objects played tricks on our expectations, bobbing on the surface as their solid counterparts surrendered to the abyss. And let’s not forget the temperature twist, where warm water and cold water threw a buoyant curveball our way.

Salinity, a salty character indeed, introduced us to the varied flavors of water. The saltwater vs. freshwater showdown was a salty drama with buoyant consequences, while layered salinity painted a picture of stratification we won’t soon forget.

In the kingdom of biology, we tipped our hats to the wonders of the natural world. Leaves and feathers showcased the genius of Mother Nature, while the origins of materials, whether from the plant kingdom or the realm of animals, whispered stories of evolution’s influence on buoyant behavior.

History beckoned us with tales of pioneers and innovators who sailed uncharted waters. Archimedes’ bathtub epiphany had us ready to hop into a tub ourselves, and the grand ships and submarines of yesteryears showed us how buoyancy played a pivotal role in human progress.

Our environmental journey was a wake-up call. Floating debris reminded us of the perils of pollution, oil spills cast shadows of despair on our watery playground, and innovative solutions pointed the way toward a brighter, cleaner future.

As we cast our final observations onto the canvas of this experiment, we couldn’t help but marvel at the complexity of our world. While our trusty hypothesis often stood its ground, the occasional curveball reminded us that nature loves to keep us guessing.

In closing, our “Sink or Float” science fair project has been more than just a lesson in buoyancy; it’s been a voyage of discovery, wonder, and excitement. We leave this experiment with a profound appreciation for the forces that shape our world and a hunger for more scientific adventures yet to come.

The journey doesn’t end here; we’re setting sail toward new horizons, eager to explore the vast ocean of knowledge that stretches before us. Until next time, let’s keep the curiosity alive and the spirit of discovery afloat!

Frequently Asked Questions

What is buoyancy?

Buoyancy is the upward force that a fluid (like water or air) exerts on an object submerged in it. It counteracts the force of gravity, allowing objects to float in a fluid if they are less dense than the fluid or to sink if they are denser.

Why do some objects float while others sink?

Objects float or sink based on their density compared to the density of the fluid they are placed in. If an object is less dense than the fluid, it will float. If it’s denser, it will sink.

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