Wasted Energy

what do most systems tend to be in practice?

In practice, most systems tend to be open systems

What term is used to describe when non useful energy transfer occurs?

dissipation

what does dissipated mean?

Dissipated means spread out

what is dissipated energy considered as?

wasted energya

what kind of energy transfers usually involve dissipated energy?

heating, light and sound

what happens when energy is transferred to an object’s thermal stores? what kind of energy transfer is it?

• When energy is transferred to the thermal stores of the objects, the temperature of the objects increases

  • The particles that make up the objects vibrate more, hence the transfer pathway is by heating (of the particles)

what is visible light?

electromagnetic radiation

what happens when light is produced?

when light is produced, energy is transferred by radiation

what kind of energy transfer occurs when sound is produced? why? (2)

• When sound is produced, the sound waves make the air particles vibrate as the wave carries energy away 

  • This increases the energy in the thermal store of the air, hence the transfer pathway is by heating (of the particles)

define useful energy

The energy that is transferred from store to store and used for an intended purpose

define wasted energy

The energy that is not useful for the intended purpose and is dissipated to the surroundings

A student uses an electric motor to lift a load.

The motor turns a mechanism that lifts the load. Some of the energy transfers are useful and the rest of the energy is wasted.

State the useful energy transfer occurring in this system.

• The motor turns the mechanism that lifts the load

• Therefore, the useful transfer is:

  • Energy in the kinetic store of the motor is transferred to the gravitational potential store of the load

A student uses an electric motor to lift a load.

The motor turns a mechanism that lifts the load. Some of the energy transfers are useful and the rest of the energy is wasted.

State the useful energy transfer occurring in this system.

• As the motor operates, friction causes a rise in the temperature of the components and the surroundings

• In this case, the energy transfer from the kinetic store of the motor to the thermal store of the motor and the surroundings is not useful, hence it is a wasted energy transfer

  • Energy is dissipated, by heating, to the surroundings

when can mechanical processes become wasteful?

Mechanical processes can become wasteful when they cause a rise in temperature

what do mechanical processes often involve?

friction

what does friction cause (3)

• When friction acts, it has the effect of transferring energy from the kinetic store by heating to the objects and the surroundings

• This energy cannot be used in a useful way, therefore it is called wasted energy

• Energy that is transferred to the surrounding is said to be dissipated (spread out) to the surroundings

what is friction a cause of?

Friction is a major cause of wasted energy in machines

describe energy wasted when a rider has been cycling for a long time

•  the gears on a bike can become hot if the rider has been cycling for a long time

  • Energy is wasted as it is transferred from the kinetic energy store of the bike to the thermal energy storeof the gears and the chain

  • This friction makes them become hot and transfers energy by heating to the thermal energy store of the surrounding air

This wasted energy can be reduced if…..

the amount of friction can be reduced

how can the amount of friction be reduced?

lubrication

what can happen if energy transferred can be prevented from dissipating? how would this be brought about?

• If this energy can be prevented from dissipating, then lessenergy will be needed to replace the wasted energy

  • This can be achieved by surrounding the appliance with insulation

list 2 things the effectiveness of insulation depends on

• How well the insulation conducts heat

• How thick the insulation is