Energy Stores & Transfers

Energy Stores

Energy can be stored in different ways within a system. The main energy stores relevant here are:

• Kinetic energy: Energy stored in moving objects. The faster an object moves, the more kinetic energy it has.
• Gravitational potential energy: Energy stored by an object because of its position in a gravitational field, usually related to height above the ground.
• Elastic potential energy: Energy stored when an object is stretched or compressed, like a spring or elastic band.
• Thermal energy: Energy stored in the internal energy of a system due to the temperature of its particles.
• Chemical energy: Energy stored in chemical bonds, such as in fuels and food, which can be released during chemical reactions.

Each store represents a way energy is held within a system before it is transferred or transformed.

Energy Transfers

Energy can be transferred from one store to another by different methods:

• Mechanical work: Energy transfer by a force moving an object through a distance, such as pushing, pulling, or lifting.
• Heating: Energy transfer due to a temperature difference, where energy moves from a hotter object to a cooler one.
• Electrical work: Energy transfer when an electric current flows through a component, doing work like lighting a bulb or powering a motor.
• Radiation: Energy transfer by electromagnetic waves, such as light or infrared radiation, which can transfer energy through a vacuum.

Understanding these transfer methods helps explain how energy moves and changes form in everyday situations.

Energy Conservation

Energy cannot be created or destroyed; it can only be transferred between stores or transformed from one type to another. This is known as the principle of conservation of energy.

When energy is transferred, some of it may be dissipated—spread out and stored in less useful forms, often as thermal energy in the surroundings. This is why machines and devices are never 100% efficient.

For example, when you rub your hands together, mechanical energy is transferred to thermal energy, warming your skin. The total energy remains the same, but some energy becomes less useful for doing work.

For instance, when a ball is dropped from a height, its gravitational potential energy decreases while its kinetic energy increases, but the total energy remains constant (ignoring air resistance). This example assumes no energy is lost to air resistance, illustrating the conservation of energy principle.

Energy Transfer Methods

Energy can move through materials and space by different methods:

• Conduction: Transfer of energy through direct contact between particles in solids. Vibrations and collisions pass energy along the material.
• Convection: Transfer of energy by the movement of fluids (liquids or gases) caused by differences in density when heated. Note that convection only occurs in fluids.
• Radiation: Transfer of energy by electromagnetic waves, which can travel through a vacuum (no medium needed).

Each method is important in different contexts, such as heating a metal rod (conduction), warming air above a radiator (convection), or feeling the Sun’s warmth (radiation).

For example, when you hold a metal spoon in a hot cup of tea, the spoon gets hot because energy is conducted along the spoon from the hot tea to your hand.