What it shows
The more sugar a liquid holds, the denser it is. By making a density scale from sugar water and then floating a small object in juice samples, you estimate how much sugar is in the juice compared with a cola or squash.
The science
Density is the mass of a liquid in a given volume. Dissolving sugar adds mass but little volume, so the density rises with sugar content. A small test object sinks in a liquid less dense than itself and floats in a denser one. By matching the juice to sugar solutions of known strength, you estimate its sugar level.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Sugar and water for a scale
- Several samples of juice, squash and cola
- A tall glass for each sample
- A kitchen scale and measuring cup
- A small grape or a ball of clay as a float
- A ruler
- A notebook
Safety
For this project: Do not drink samples that have been handled with the test objects. Wash everything afterwards and do not share glasses.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Prepare sugar solutions with 0, 5, 10, 15 and 20 g of sugar in 100 ml of water.
Weigh 100 ml of each solution and calculate its density as mass divided by volume.
Drop a small test object in each glass and note whether it sinks, hangs in the middle or floats.
Find the solution whose density matches the object, by trying small steps between solutions.
Weigh 100 ml of each juice sample and calculate its density.
Compare the juice densities with the sugar scale to estimate their sugar content in g per 100 ml.
Check the pack label for sugar content and compare it with your estimate.
What you should see
The densities of the juices lie between water and the strong sugar solution, and the densest ones match the sugariest labels. Your estimates agree with the pack labels within a few grams.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1How do you calculate density?
Mass divided by volume.
2Why does sugar raise the density?
It adds mass without adding much volume.
3When does an object float?
When it is less dense than the liquid.
4Why is the estimate not exact?
Juice has other dissolved substances and pulp.
Take it further
Draw a calibration graph of density against sugar and use it to read off an unknown sample.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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