Density Of Different States | Matter | Physics | FuseSchool

Density Of Different States | Matter | Physics | FuseSchool

Why is it easy to lift up a big inflated beach ball but much harder to lift a small heavy pebble? It is largely to do with density, the small pebble is more dense and the Big Bite beach is less dense.

In this video we are going to look at what density is, how it is measured and the differences in density between the different states of matter. Informally, density is a measure of how ‘packed’ a material is with mass. Density is defined as the mass of an object per its unit volume. So the big beach ball has a small mass but a big volume, meaning it’s density is low. Whereas the pebble is the opposite - lots of mass compacted into a small volume.

Rank these objects in terms of destiny from least dense to the most dense. Pause the video, have a think and click play when you're ready. Did you get them ready?

Did you know that liquids and gases also have different densities? Look at this density tower of different liquids. The honey is most dense and so sinks to the bottom, whereas milk is in the middle and lamp oil is the least dense. But what about densities between different states? Look at the world around you… think of floating and sinking. When you go to the beach, why does the big beach ball float whereas the small heavy pebble sinks? Why do huge boats float? How come a heavy, wooden log floats on water but a small, lighter paper clip sinks? This is all to do with density!

Air is less dense than water… the beach ball, boat and wooden log are also less dense than water, hence they float. But the pebble and the paper clip are more dense than water, and so sink.

Don't be fooled into thinking that gases are pretty much always the least dense, don’t be fooled into thinking that liquids are always less dense than solids. This just isn’t the case! Density is how heavy an object is for it’s size.

To calculate the density of an object divide its mass in kilograms by its volume in cube metres. These are the units used for density.
Using this formula gives these density question a go. Notice that question three is a little different.

So, from the formula we saw that density is based on the mass and size of an object but it is also based on the arrangements of the atoms it's made of.

Inside each object are atoms and molecules. How closely these atoms and molecules are packed together and how massive each atom is determines the density. In the rock, the molecules are squished tightly together whereas in wood they are more spread out, and in air much more spread out.

A final thought… think of icebergs - they float on water, so solid ice is less dense than liquid seawater. When the ice melts, so it changes temperature, it becomes more dense and so mixes with the seawater. This means that temperature does affect density. This relationship between temperature and density explains how hot air balloons work… hot air is less dense than the cooler normal air, and so the cooler denser air underneath them pushes the hot air balloons upwards. Hot water is also less dense than cold water, so the top of the ocean is warmer than the bottom. So there we have density. It is a comparison of how heavy an object is compared to it’s size, and also includes the arrangement of atoms inside it.


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