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Grade 9 Physics - Energy (Cambridge GSCE O-level Core Standard)
Energy
The ability to do work.
Is energy a vector or a scalar quantity?
Scalar quantity, as direction isn’t important.
Work done
The force applied multiplied by the distance travelled in the direction of the force.
Formula of Work done
W.D = F x s
Power
The rate at which energy is used. (How much energy is used per second)
Formula of Power
P = E/t
Potential Energy (Stored Energy)
The energy a body has because of its position or condition.
The three different types of potential energies are…
Chemical P.E, Elastic P.E, Gravitational P.E
Gravitational Potential Energy
Found in all objects which are at some height above the ground.
Formula of Gravitational P.E
Gravitational P.E = m x g x h
Kinetic Energy
The energy a body has for its motion.
Formula of Kinetic Energy
KE = mv² / 2 or ½ x mv²
Principle of Conservation of Energy
Energy is neither created nor destroyed, but is always conserved (Changing from one form to another.).
Formula for efficiency (of electrical appliances)
Useful Energy Output/Total Energy Input x 100
What happens when an object falls from a height above the ground?
Gravitational P.E → Kinetic Energy → Sound Energy, Heat Energy, and W.D to break the object and/or the ground
Formula of efficiency (Of a ramp)
W.D against gravity/W.D by person x 100
What are the types of energies which are wasted when using a ramp?
Sound energy
W.D against Friction: Wasted due to friction between the object and the ramp surface.
Heat energy
What if a ramp has no friction?
This means that there are no energy losses. Therefore W.D by person = W.D against Gravity (Efficiency = 100%)
Energy transfer in a boiler (Power Station)
Chemical Potential Energy → Heat Energy
Energy transfer in a turbine (Power Station)
Heat Energy → Kinetic Energy
Energy transfer in a generator (Power Station)
Kinetic Energy → Electrical Energy
Wasted energy in a power station
Heat Energy and Sound Energy
Note
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