physics test monday

Mass

The amount of matter in an object, measured in kilograms ($kg$).

Acceleration due to gravity ($g$)

Acceleration caused by gravity, which on Earth is approximately $9.8\,m/s^2$ (often rounded to $10\,m/s^2$).

Weight

The gravitational force acting on an object, measured in newtons ($N$).

Difference between mass and weight

Mass is the constant amount of matter in an object, while weight is the gravitational force acting on it and varies with gravitational field strength.

Equation for weight

$$W = m \times g$$

Energy

The ability to do work, measured in joules ($J$).

Kinetic energy

The energy an object possesses due to its motion.

Gravitational potential energy

The energy stored in an object due to its height within a gravitational field.

Elastic potential energy

The energy stored when an object is stretched or compressed.

Chemical potential energy

The energy stored in chemical bonds, such as in food or fuels.

Nuclear potential energy

The energy stored in the nucleus of an atom.

Sound energy

The energy carried by vibrations travelling through a medium.

Light energy

The energy carried by electromagnetic radiation that can be detected by the human eye.

Heat (thermal) energy

The energy associated with the movement and vibration of particles in matter.

Electrical energy

The energy transferred by moving electric charges.

Law of Conservation of Energy

Law stating that energy cannot be created or destroyed, only transferred or transformed.

Difference between energy transfer and energy transformation

Energy transfer moves energy from one place or object to another, whereas energy transformation changes energy from one form to another.

Example of energy transfer

Heat conducting from a hot object to a cooler object.

Example of energy transformation

A light bulb transforming electrical energy into light and thermal energy.

Unit of energy

Joule ($J$).

Joules in 1 kilojoule ($1\,kJ$)

$$1000\,J$$

Joules in 1 megajoule ($1\,MJ$)

$$1\,000\,000\,J$$

Equation for kinetic energy

$$KE = \frac{1}{2}mv^2$$

Variables in kinetic energy equation ($KE = \frac{1}{2}mv^2$)

$KE$ is kinetic energy in joules ($J$), $m$ is mass in kilograms ($kg$), and $v$ is speed in metres per second ($m/s$).

Equation for gravitational potential energy

$$GPE = mgh$$

Variables in gravitational potential energy equation ($GPE = mgh$)

$GPE$ is gravitational potential energy in joules ($J$), $m$ is mass in kilograms ($kg$), $g$ is gravitational acceleration ($m/s^2$), and $h$ is height in metres ($m$).

Effect of increasing mass on kinetic energy

Kinetic energy increases proportionally if speed remains constant.

Effect of increasing speed on kinetic energy

Kinetic energy increases significantly because speed is squared in the formula.

Effect of increasing mass on gravitational potential energy

Gravitational potential energy increases proportionally if height remains constant.

Effect of increasing height on gravitational potential energy

Gravitational potential energy increases proportionally.

Example of kinetic energy transforming to gravitational potential energy

A ball thrown upwards loses kinetic energy and gains gravitational potential energy as it ascends.

Equation for power

$$\text{Power} = \frac{\text{Energy}}{\text{Time}}$$

Unit of measurement for power

Watt ($W$).

Motor

A device that transforms electrical energy into kinetic energy.

Generator

A device that transforms kinetic energy into electrical energy.

Renewable energy source

An energy source that is naturally replenished on a human timescale and does not run out.

Non-renewable energy source

An energy source available in limited amounts that takes millions of years to form.

Examples of renewable energy sources

Solar, wind, hydroelectric, geothermal, and biomass.

Examples of non-renewable energy sources

Coal, oil, natural gas, and nuclear fuels such as uranium.

Advantage of renewable energy

Produces little or no greenhouse gas emissions during operation and naturally replenishes.

Disadvantage of renewable energy

Often depends on weather conditions and may not generate power continuously.

Advantage of non-renewable energy

Provides a large, reliable supply of energy on demand.

Disadvantage of non-renewable energy

Finite in supply and releases greenhouse gases and pollutants when burned.

Energy transformations in a coal power station

Chemical energy (coal) \rightarrow thermal energy \rightarrow kinetic energy (steam/turbine) \rightarrow kinetic energy (generator) \rightarrow electrical energy.

Common forms of energy loss in systems

Unwanted thermal energy and sound transferred to the surroundings.

Thermal energy at particle level

The kinetic energy associated with the movement and vibration of particles within matter.

Conduction

The transfer of thermal energy through direct contact between particles without bulk movement of the material.

Thermal conductor

A material that allows thermal energy to pass through it easily.

Thermal insulator

A material that slows down or resists the transfer of thermal energy.

Difference between thermal conductors and insulators

Conductors transfer thermal energy rapidly, whereas insulators significantly slow thermal transfer.

Convection

The transfer of thermal energy through the bulk movement of particles in a fluid (liquid or gas).

Formation of convection currents

Heating causes fluid to expand and become less dense, causing it to rise, while cooler, denser fluid sinks to replace it.

Reason warm fluid rises

It expands upon heating, making it less dense than the surrounding cooler fluid.

Reason cool fluid sinks

It has a higher density compared to surrounding warmer fluid.

Thermal radiation

The transfer of thermal energy by electromagnetic waves, primarily infrared radiation.

Medium requirement for thermal radiation

Does not require particles or a physical medium; it can travel through a vacuum.

Interactions of materials with thermal radiation

Materials can absorb, reflect, or transmit thermal radiation.

Absorption of thermal radiation

The process where a material takes in radiation, causing its thermal energy to increase.

Reflection of thermal radiation

The process where radiation bounces off a material's surface without being absorbed.

Transmission of thermal radiation

The process where radiation passes directly through a material.

Best absorbers and emitters of thermal radiation

Dark, dull (matte) surfaces.

Poor absorbers/emitters (good reflectors) of thermal radiation

Light, shiny surfaces.