Wasted Energy
- Mechanical processes can become wasteful when they cause a rise in temperature
- These processes often involve friction
- 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
- Useful energy can be defined as:
An energy transfer that serves an intended purpose
- Wasted energy can be defined as:
An energy transfer that is not useful for the intended purpose and is dissipated to the surroundings
Example: A Bat Hitting a Ball
- The moving bat has energy in its kinetic store
- Some of that energy is transferred usefully to the kinetic store of the ball
- Some of that energy is transferred from the kinetic store of the bat to the thermal store of the ball mechanically due to the impact of the bat on the ball
- Some of that energy is dissipated by heating to the thermal store of the bat, the ball, and the surroundings
Energy transfers taking place when a bat hits a ball
Worked example
A student uses an electric motor to lift a load.
As the motor turns, energy is transferred to the load as the string and the pully lift it up.
a) State the useful energy transfer happening in this system.
b) State the main wasted energy transfer happening in this system.
Part (a)
-
- The motor turns so it is moving, therefore energy is transferred from the kinetic store of the motor
- The load is lifted upwards (through a gravitational field) by the string and pulley, therefore energy is transferred usefully to the gravitational potential store of the load
Part (b)
-
- As the motor operates, friction between the components causes heating
- Therefore, energy is transferred from the kinetic store of the motor to the thermal store of the motor and dissipated to the surroundings
Examiner Tip
Make sure you are able to identify "useful" and "wasted" energy transfers as this is commonly tested in exams!
Learn the term 'dissipated to the surroundings', because if you say the energy is simply "lost", this will not gain you the mark as it implies that energy is not conserved.