IGCSE PHYSICS
CONDITIONS FOR EQUILIBRIUM
By Yaejong Lee
Equilibrium
When a number of forces acting on
a body produce no change in its
state of rest , the body is said to be
in equilibrium.
The sum of the anticlockwise
moments about any point must be
equal to the sum of the clockwise
moments about the same point.
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Conditions for Equilibrium
• There are two conditions for the body to be in equilibrium
1.) The resultant of all the forces acting on the body should be equal to
zero
2.) The resultant moment of all the forces acting on the body about a
point should be zero
• Principle of moment
In equilibrium the sum of the clockwise moments about any point must
be equal to the sum of the clockwise moments about the same point.
This is called the principle of moments
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IGCSE PHYSICS
POTENTIAL AND KINETIC ENERGY
By Yaejong Lee
Potential energy
Potential energy is the energy stored
in an object as a result of it position.
◦ For example a pulled spring is
able to store energy as the result
of its position. When not pulled
at there is no energy stored in the
spring but when the position is
altered from its equilibrium
position, the spring is able to store
energy. This stored energy is
referred to as potential energy.
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The formula to calculate the potential
energy of an object is the mass of the
object times the acceleration due to
gravity (9.8 𝑚/𝑠 2 ) times the height of the
object.
𝑃. 𝐸 = 𝑚𝑔ℎ
The mass of the object times the
acceleration due to gravity is the
weight of an object. Therefor Potential
energy is the weight of the object time
the height.
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Kinetic energy
Kinetic energy is the energy
of motion.
Kinetic energy depends on the
mass of the object as well as the
speed of that object.
Kinetic (derived from the Greek
root word “ kinein” which
means “to move”)
𝐾. 𝐸 = 1/2𝑚𝑣 2
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