Physics - Chapter 7 - Energy

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