Chpt 1 - Conservation & dissipation of energy

What is a system?

An object or group of objects

What is a closed system?

A group of objects that transfer energy only to each other. Energy can't escape or enter from its surroundings.

What is work done?

A transfer of energy, as a result of a force acting on an object. If the work is done on an object, it gains energy; if the work is done by an object, it loses energy. The total amount of energy remains the same (it is conserved).

Equation for work done

Work done = force x distance

State the law of conservation of energy

Energy cannot be created or destroyed, it can only transferred from one place to another.

What is energy measured in?

Joules (J)

Name the 8 energy stores

1) Thermal
2) Kinetic
3) Gravitational potential
4) Elastic potential
5) Chemical
6) Magnetic
7) Electrostatic
8) Nuclear

What is kinetic energy?

Energy of movement

What is gravitational potential energy?

Energy that an object has depending on its height

What is thermal (or internal) energy?

Energy that an abject has depending on its temperature

What is chemical energy?

Energy stored in chemical bonds (e.g. food etc.)

What is nuclear energy?

Energy stored in the nucleus of an atom

What is magnetic energy?

The energy stored when repelling poles have been pushed closer together or when attracting poles have been pulled further apart. magnets

What is electrostatic energy?

Energy a charged object has when near another charged object

Name the 4 energy transfers

1) Mechanical
2) Electrical
3) Heating
4) Radiation

Equation for kinetic energy

Ke = 1/2m v^2

Equation for elastic potential energy

Ee = 1/2 k e^2

Equation for gravitational potential energy

GPE = mgh

What is power?

The rate at which work is done

Equation for power

P = W/t

What is power measured in?

Watts (W)

What can you do to reduce energy dissipated and wasted to surroundings?

1) Lubrication
2) Streamlining
3) Insulation

All energy ends up transferred to the thermal energy store of the surroundings. Why?

Friction causes the energy transfer to thermal energy.

What is lubrication?

A way of reducing unwanted energy transfer due to friction

What is streamlining?

A way of reducing energy wasted due to air resistance or drag in water

What is insulation?

A way of reducing energy wasted due to heat dissipation

What is efficiency?

Efficiency is a measure of how much energy is transferred usefully

Equation for efficiency

Efficiency = useful energy output/total energy input