ARCHIMEDES PRINCIPLE
GRADE 8
STANDARD COMPETENCE
3.8 Describe the pressure of substances and their application in everyday life,
including blood pressure, osmosis, and capillarity of transport tissue in plants
OBJECTIVES
Measure the buoyant force acting on an object
Solving problems about buoyant force
What is the
Archimedes’
Principle?
• Archimedes’ principle
states that:
An object immersed in a liquid
experiences an upward force
(buoyant force),
How to measure a buoyant force?
Buoyant Force
weight of the object on air
weight of the object on water
Loss in weight
= buoyant force
Buoyant force is equal to the weight of the fluid
displaced.
Archimedes’ Principle Formula
• In simple form, the Archimedes law states that the buoyant
force on an object is equal to the weight of the fluid displaced
by the object. Mathematically written as:
Fb = ρ x g x V
Where:
ρ is the density of the liquid,
V is the volume of liquid displaced and
g is the acceleration due to gravity.
Problem 1
1. Archimedes immersed a gold crown with the mass of 0.5 kg completely
under water. If the volume of water spilled was 50 cm3, the buoyant force
acting on the gold crown was...
(density of water = 1000 kg/m3 , and g = 10 N/kg)
A. 0.25 N
B. 0.50 N
C. 2.50 N
D. 5.00 N
Problem 2
2. An object in the form of a block having a volume of 22.5 m3 is fully
submerged in water. If acceleration of gravity g= 10 m/s2 and density of
water 1,000 kg/m3, then the magnitude of bouyancy force acting on the
object is ....
Types of Buoyancy
1. Positive buoyancy : Floats
If Buoyant force > weight of the object
If density of water > density of the object
2. Neutral buoyancy : Hover
If Buoyant force = weight of the object
If density of water = density of the object
3. Negative buoyancy : Sinks
If Buoyant force < weight of the object
If density of water < density of the object
Problem 3