You will need:
- One gold ring.
- One ‘cheap’ metal ring that looks like gold
- Two glasses of water, filled to the brim.
- Good scales or a beam balance.
- Fine cotton thread.
- Permission to use someone’s ring!
You are doing two separate calculations, so record your results for ring experiment one and two separately.
Weigh both glasses, which are filled to the brim with water.
Write down each mass and write the letter ‘B’ next to each mass.
Tie the cotton thread around each ring and slowly dip the ring into the water.
Let the water spill over the glass.
Take the ring out of the water and re-weigh each glass of water. Write the mass of each down and label this as ‘C’
For each experiment perform the following calculation:
(B – C) / A = Specific gravity of the ring.
Are there any sources of error?
E.g. It’s easier to measure greater volumes of displaced water. Why not try comparing iron vs rock?
If the ‘cheap’ ring is real gold, its specific gravity should be the same as for the real gold ring. Of course, this experiment would be much easier to measure with a larger golden nugget!
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Why Does This Happen?
Specific gravity is the ratio of an objects mass in a given volume, compared to water.
Gold is a very heavy metal, with it’s specific gravity being about 19.3… more than twice Lead!
There is a story that the Greek philosopher Archimedes who once used the displacement of water to work out if the King’s crown was made of real gold… he found out that it was partly fake!
How?
He compared the king’s gold crown against another gold crown with the same weight.
He found that the king’s crown displaced more water than the other crown.
Why?
The king’s crown had some silver in it, making it less dense.
So for the king’s crown to weigh the same as a real gold crown it’s volume had to be bigger.
i.e. the king’s gold crown had a specific gravity lower than the real gold crown.
From volume and length through to statistics and trigonometry, the Working Mathematically workshop has your mathematics enrichment covered!
Get in touch with FizzicsEd to find out how we can work with your class.
Working Mathematically
Years 3 to 6
Maximum 30 students
School workshop (NSW only)
90 minutes or Full Day
Online Class Available
STEM Full Day Accelerator - Primary
Designed from real classroom experiences, this modular day helps you create consistently effective science learning that directly address the new curriculum with easily accessible and cost-effective materials.
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