Forces and Energy Revision

Comprehensive vocabulary flashcards covering the Year 8 physics revision checklist on forces, mass and weight, Newton's laws, pressure, energy stores and transfers, power generation, and heating methods.

Contact force

A force that acts between objects that are physically touching, such as friction, drag (air or water resistance), upthrust, thrust, tension, or normal (support) force.

Non-contact force

A force that acts on an object at a distance without physical contact, such as gravity, magnetic force, or electrostatic force.

Force arrow

A diagrammatic representation of a force where the arrow points in the direction the force acts, and a longer arrow indicates a bigger force.

Mass

The amount of matter in an object, measured in kilograms ($\text{kg}$), which never changes regardless of location.

Weight

The downward force acting on an object due to gravity, measured in Newtons ($\text{N}$) and calculated using $W = m \times g$.

Gravitational field strength ($g$)

The gravitational force per unit mass, having values of $10\,\text{N/kg}$ on Earth, $1.6\,\text{N/kg}$ on the Moon, and $4\,\text{N/kg}$ on Mars.

Resultant force

The single overall force acting on an object, calculated by adding forces that act in the same direction and subtracting forces that act in opposite directions.

Balanced forces

Forces acting on an object that cancel each other out completely, causing the object to either stay still or keep moving at the same speed and direction.

Unbalanced forces

Forces acting on an object that do not cancel out, resulting in a non-zero resultant force that causes the object to speed up, slow down, or change direction.

Steady speed of a falling object

The constant speed reached by a falling object when the upward drag force increases with speed until it equals the downward weight.

Pressure

The force applied per unit area, given by $p = F \div A$, measured in Pascals ($\text{Pa}$) when area is in $\text{m}^2$, or $\text{N/cm}^2$ when area is in $\text{cm}^2$.

Friction

A contact force that acts against motion, which can be increased for grip by using rougher surfaces, tyres with tread, or adding more weight.

Drag

Air or water resistance that opposes the motion of an object travelling through a fluid, which can be reduced by streamlining or travelling slower.

Newton's first law

The physical law stating that objects keep doing what they are doing (staying still or moving at constant speed and direction) unless a resultant force acts on them.

Newton's second law

The law describing the relationship between resultant force, mass, and acceleration, given by $F = m \times a$ and rearranged as $a = F \div m$.

Newton's third law pair

A pair of forces of equal size that act in opposite directions on two different objects.

Energy stores

The distinct forms in which energy can be stored within a system: kinetic, gravitational potential, elastic, chemical, and thermal.

Energy transfer pathways

The four methods by which energy moves between stores: mechanically, electrically, by heating, and by radiation.

Conservation of energy

The principle stating that energy is never created or destroyed; wasted energy is simply dissipated to the surroundings.

Efficiency

A percentage measure of how much total input energy is turned into useful output energy, calculated as $\text{efficiency} = \frac{\text{useful energy out}}{\text{total energy in}} \times 100\%$.

Sankey diagram

A graphic representation of energy transfers where the width of each arrow shows the exact amount of energy transferred.

Thermal power station sequence

The operational sequence in most power stations: fuel burns $\rightarrow$ boiler heats water to steam $\rightarrow$ steam spins turbine $\rightarrow$ generator generates electricity.

Temperature

A measurement of how hot or cold an object is, measured in degrees Celsius ($^\circ\text{C}$).

Thermal energy

The total heat energy stored within an object, measured in Joules ($\text{J}$), which depends on both its temperature and the total quantity of matter.

Conduction

The transfer of thermal energy through a material as vibrating particles pass energy on to neighbouring particles, aided by free electrons in metals.

Convection

Thermal energy transfer in a fluid where warm fluid expands, becomes less dense, and rises, while cool, denser fluid sinks.

Thermal radiation

Energy transfer via infrared waves that requires no particles to travel; matt black surfaces are the best emitters and absorbers.

Insulation

Methods or materials that reduce heat transfer, typically using trapped air because air is a poor conductor and trapping it stops convection currents.

Vacuum flask

A container designed to minimize thermal energy loss; its vacuum contains no particles, preventing conduction and convection across it.

Explain (command word)

An assessment instruction that requires saying why a process happens or giving scientific reasons for an answer.

Evaluate (command word)

An assessment instruction requiring the consideration of both sides of an issue or dataset followed by making a reasoned decision.