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# Form 4 Physics: Floating and sinking online lessons

Experiment: to demonstrate Archimedes principle with a worked example

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Experiment: To demonstrate Archimedes principle:
Procedure
1. Pour water into an overflow can (eureka can) until it starts to flow out then wait until it stops dripping
2. Tie a suitable solid body securely and suspend it on a spring balance. Determine weight in air.
3. Lower the body slowly into the overflow can while still attached to the spring balance then read off its weight when fully submerged.
4. Weigh the displaced water collected in a beaker. Record your readings as follows;
Weight of body in air = W1
Weight of body in water = W2
Weight of empty beaker = W3
Weight of beaker and displaced liquid = W4
Upthrust of the body = W1 –W2
Weight of displaced water =W4 –W3

Discussion
The upthrust on the solid body will be found to be equal to the weight of displaced water therefore demonstrating the Archimedes principle.
Example
A block of metal of volume 60 cm^3 weighs 4.80 N in air.
Determine its weight when fully submerged in a liquid of density 1,200 kgm^-3.
Solution:
Volume of liquid displaced = 60 cm^3 = 6.0 times 10^-5 m^3.
Weight of the displaced liquid= volume × density × gravity =v × ρ × g
= 6.0 times 10^-5 times 1200 times 10
= 0.72 N
Upthrust = weight of the
liquid displaced.
Weight of the block in the
liquid = (4.80 – 0.72) = 4.08 N.

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