Density



Just like all matter water has physical properties that can be measured and calculated. To find the mass of water you will need a beaker and a scale. First find the mass of the empty beaker. Next, fill up the beaker to your desired amount. Then use the scale to find the mass of the filled beaker. To find the mass of just the water, subtract the mass of the empty beaker from the full beaker. Our sample is 100 grams.

The volume of water can be measured using a graduated cylinder. Our sample is 100ml.

Density is calculated by dividing the mass by the volume. Plug in our measured mass at 100 grams and divide that by our measured volume of 100 ml. Water’s density is 1 g/ml.

Objects with a density greater than 1g/ml will sink when placed in water. Objects with a density less than one will float when placed in water. If a block has a density of 0.1g/cm3 it will float because it’s density is less than 1. Another block with a density of 0.5g/cm3 will also float because its density is less than 1. Notice that more of the block is below the waterline. A block with a density of 0.9g/cm3 is more dense so more of the block will be below the waterline. We can see that as density increases more of the block is below the waterline. Scientists have discovered that the blocks density will tell us exactly where the block will come to rest. If the density is 0.1g/cm3 then 10% will be below the waterline. To calculate where a block will come to rest just convert the density to a percent.

Density explains why ice floats. If you freeze water it expands. The black dots represent the atoms in water. No new atoms were are added to the water so because of the expansion there is more room between the atoms. Compared to the atoms in liquid water, the atoms in the ice are not as tightly packed together causing the ice to float. Try calculating density of ice for yourself. If you get a number less than one it will float. You can also predict how much of it will be below the waterline.

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