thickness can sometimes be a tricky ide for students to understand. You can"t easily estimate an object"s density by merely looking at it. You have to think about the relationship in between two of its properties:mass and also volume.

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In this activities, students will find out about mass, volume and also density and also their connection to each other by conducting investigations right into buoyancy: floating (and sinking) objects used in their day-to-day lives.


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show how the circulation of molecule in a substance determines the density.

Investigate the relative densities the liquids and also the relative densities of solids.

Predict, test and also explain relative density by investigate the interaction of liquids and solids.

Demonstrate knowledge of the relationship between density and also buoyancy by structure a boat.


watch individual activities for materials.


Density, massive & VolumeSimply put, density is exactly how tightly “stuff” is packed into a characterized space.

For example, a suitcase jam-packed with clothes and also souvenirs has a high density, when the same suitcase containing two pairs the underwear has actually low density. Size-wise, both suitcases look at the same, but their density depends ~ above the relationship between their mass and also volume.Mass is the lot of matter in an object.Volume is the quantity of room that an object takes up in 3 dimensions.

Density is calculated utilizing the complying with equation: Density = mass/volume or D = m/v.

Let’s compare three acquainted substances to discover the concept of density. If we take the very same volume (one cubic centimetre) the foam, wood and concrete, we have the right to see the each has actually a various mass.


Less Dense, an ext DenseIf other is hefty for that is size, it has actually a high density. If an object is light for its dimension it has actually a short density.

A pebble is heavy for the size, compared to a piece of popcorn i m sorry is light for it’s size. Imagine a huge bowl the popcorn, compared to a huge bowl the pebbles, which would certainly feel heavier?

It is basic to estimate relative densities if you store either the volume or the mass of two objects the same.

If girlfriend filled one bag through a kg that feathers and also another with a kg of lead you would check out that the feathers take up much an ext room, also though both bags have actually the exact same mass. This because feathers are much less dense, they have less mass per volume. If girlfriend made a copper cube and an aluminum cube the the same volume and placed one in each hand, girlfriend would have the ability to feel that the copper cube would certainly be heavier. Copper has an ext mass every volume than aluminum.


How have the right to one problem have more mass every volume 보다 another? There space a few possibilities:

Atoms the one substance could be a similar size however have more mass 보다 the atom of one more substance.Atoms that one substance could be a comparable mass however be smaller, so much more of castle fit in ~ the exact same volume.Atoms of one substance can be arranged in a method that allows more of them to fit in the exact same volume.

Any one or a combination of these explanations could be the reason why one substance has a greater density 보다 another. In the case of copper and aluminum, their atoms are arranged similarly, however copper atom are smaller sized and have more mass than aluminum atoms, offering it a higher density.


Density, Sinking and FloatingWhy perform some things float, while rather sink? You might expect heavier objects come sink and also lighter ones come float, but sometimes the contrary is true. The relative densities of things and the liquid it is inserted in identify whether that object will sink or float. Things that has actually a greater density 보다 the liquid it’s in will sink. An object that has actually a lower thickness than the fluid it’s in will float.

You can really see relative densities at work-related when girlfriend look at a heavy object floating and a lighter one sinking. For example, imagine placing a tiny piece that clay and also a large, hefty wax candle in a bathtub of water. Also though it’s lighter, the item of clay has a higher density 보다 water and therefore sinks. Even though it’s heavier, wax has a lower density than water, so the huge candle floats.


Sinking and floating applies to liquids too. For example, if you add vegetable oil to water, the oil floats on top of the water because the oil has actually a lower thickness than the water.

Buoyancy and Archimedes’ PrincipleThe ancient Greek thinker Archimedes found that when an item is submerged in water, the pushes aside (or displaces) an quantity of water with the exact same mass together the object.

The water pushes upward versus the object with a force (buoyancy) equal to the load of water the is displaced.

Let’s explore Archimedes’ rule by dropping a bowling ball right into a bath tub of water. When the ball is submerged in the water, it displaces that is volume in water. Follow to Archimedes’ principle, the water can “push back” with a pressure equal come the load of the water that has actually been displaced.


A litre of water has a density of 1 kilogram every litre (1 kg/L), so a bowling ball’s worth of water (4.5 L) deserve to push ago on the bowling sphere with a pressure equal to 45 newtons (N). That’s the weight of a 4.5 kg mass. However, the load of the ball is much more like 55 N. That’s much more than the buoyant pressure of the water it displaced, so that sinks.

A beach round may have the very same volume together a bowling ball, but it has actually a lot smaller mass. When you a beach sphere in a bath tub of water, it displaces the mass of water same to its own mass—about 0.01 kg. If you to be to shot to press the beach ball down and also displace an ext water, the water would certainly push earlier with a pressure greater than the load of the beach ball. The press of the water keeps the beach sphere afloat.

Buoyancy is the upward pressure we need from the water to continue to be afloat. Buoyant forces are why us feel so much lighter when we space in a swimming pool. Our bodies are mostly water, therefore our density is reasonably close to the of water. Due to the fact that of this, an average person needs only a tiny bit extra buoyancy come float. A life jacket offers this extra lift.

Changing DensityYou can readjust the density of a substance by heating it, cooling it, or by adding something come it. If an item sinks in water, it’s because the object has a greater density 보다 the water. There space two feasible ways come make that object float, however:

Increase the density of the water so the the water i do not care denser than the object. For example, an egg will usually sink in a glass the water, because it is denser than water. Including salt to the water boosts the thickness of the water, permitting the egg to float. This experiment additionally works through people, yet you require a most salt (try the ocean, or also better, the Dead Sea !)
Increase the volume the the thing so the the thing becomes less dense than the water. A an excellent example that this is ice floating in water. Ice cream is formed by freezing water. Once it freezes, it rises in volume as the water molecules relocate farther apart to accommodate the lattice structure of ice. Due to the fact that the ice is now less thick than water, the floats. This phenomenon likewise explains why pearls float also though they space made of steel. A delivery is built in together a way that that encloses big amounts of open up space. The delivery still displaces its weight in water, but due to the fact that of the method the delivery is constructed, that takes up much more space 보다 the volume that the water it displaces, so the floats.


Archimedes: Greek mathematician, physicist, engineer, inventor and astronomer (c. 287 BC–c. 212 BC).Archimedes’ principle: any type of object wholly or partly immersed in a liquid is lifebuoy by a force equal to the load of the fluid that is displaced by the object. In various other words, the buoyancy is equal to the weight that the displaced fluid.buoyancy: The upward pressure that a liquid exerts on an item less thick than itself; the ability come float.density: How very closely packed together the molecules of things or problem are.displace: To press out the the way. For example, when an item goes into water, it displaces the water.immiscible: can not to be mixed together, prefer oil and water.ironwood: The surname for a large number that woods that have actually a reputation for hardness and high density.mass: The amount of matter in a provided space.matter: The substance that provides up every physical things.pumice stone: Lava froth well-known for its small mass and low density, in spite of looking prefer a rock.weight: A measure up of the pressure of gravity on an object.

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volume: The lot of room a problem or object takes up.