Science Friday: exploring Density

This week we used a Gizmo to explore Density.

Screen Shot 2013-02-07 at 7.21.03 PM

We were able to calculate density by dividing the weight in grams by the volume of liquid (in mL) displaced by the object when it is placed in the graduated cylinder. She already knew how to do this from the Mineral Identification experiments we’d performed previously. We then recorded the densities of various items from the shelves and also noted in which liquids they sank or floated (or sank slowly). The drop down menu above the large beaker allowed us to choose between water, oil, gasoline, seawater, and corn syrup.

When we had recorded these data for a few items I asked her to see if she noticed a pattern. This is the “observation” part of the scientific method. She noticed that objects with high density sank in all liquids, whereas objects with low density floated in all liquids or in some of the liquids. I then asked her to make predictions – hypotheses – and test them.

We had already determined that the gold nugget, with a density of 19.3, sank in all liquids; the chess piece, with a density of 0.5, floated in all liquids; and the egg, with a density of 1.0 floated in corn syrup and saltwater but sank in water, gas, and oil. She found that the golf ball floated in corn syrup but sank in all the other liquids so she hypothesized that its density would be greater than 1 but much less than 19. When measured it was 1.25.

Next she dropped each crown into all of the liquids. Both crowns sank in all the liquids tested, so she hypothesized that their densities would be equal. However, when she measured them she found that while both crowns displaced 100 mL of water, they had different weights. The density of crown 1 was 8.4 and crown 2 was 19.3. From these observations she then hypothesized that anything with a density greater than 8 would sink in all the liquids. She used the rock to test her hypothesis: it sank in everything as predicted. However, its density was 4.

She finished by doing the quiz associated with the lesson and scored 5/5.


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