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8.3 Buoyancy: Archimedes’ Principle
People have sailed on Upthrust force
rafts, boats and ships There is a pressure in liquid that differs depending
since ancient times. on the depth. As a result, any object immersed in
Such vessels used to liquid experiences a force trying to push this object
textbooks nis edu kz
be made of wood but out – the upthrust force.
nowadays passenger Archimedes was the ancient Greek scientist
and cargo ships for who discovered the force of buoyancy and first Archimedes
rivers and seas are calculated its magnitude. (287–212 bce)
built using different EXT Imagine you are a scientist and inventor. Write an article for a
materials. Yet they all scientific magazine about the technical inventions of Archimedes.
float. Why does a heavy
Upthrust force is calculated using this equation:
ship not sink but a light
Upthrust (Archimedes’) force = density of liquid × acceleration of
stone thrown into the
gravity × volume of object immersed in liquid
water go straight down
to the bottom? F A = l ob
g = 9.8 N/kg
Archimedes’ Principle
F A
When a load is immersed in water
in a container, it displaces (pushes
F T
out) some of the water, as shown
in the image. The weight of this
water equals the Archimedes’
Density of object is less
than density of liquid. (upthrust) force.
upthrust (Archimedes’ force) = weight of liquid in submerged
volume of object = mass of liquid in submerged volume of
F A
object × constant g
F A = l = m l ∙ g
g = 9.8 N/kg
F T
Density of object is equal Buoyancy
to density of liquid.
If the gravity force acting on an object in liquid is less than the upthrust
(Archimedes’) force, then the object will float on the surface of the
liquid. If the gravity force is equal to the upthrust force, then the object is
in equilibrium at any place within this liquid. If the gravity force is greater
than the upthrust force, then the object sinks and rests at the bottom.
F A
F T
Density of object is greater
than density of liquid.
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