Forms of Energy
Explore the different forms of energy — kinetic, potential, thermal, light, sound, electrical, and chemical — and understand how energy transforms from one form to another.
What is Energy?
Energy is the ability to do work — to cause an object to move, change temperature, or change state. Energy cannot be created or destroyed; it can only be transformed from one form to another. This is the Law of Conservation of Energy.
Energy is measured in joules (J). Larger amounts are measured in kilojoules (kJ) — for example, the energy in a Tim Tam biscuit is about 330 kJ.
Australian Curriculum Connection
This lesson aligns with AC9S7U04: "Energy can be transferred and transformed; different forms of energy include light, heat, sound, electrical, chemical, and kinetic and potential energy."
The Seven Main Forms of Energy
Kinetic Energy
The energy of moving objects. The faster an object moves, or the more massive it is, the more kinetic energy it has. A cricket ball flying through the air has kinetic energy.
KE = ½ × mass × velocity²
Potential Energy
Energy stored due to position or condition. A rock on a cliff has gravitational potential energy. A compressed spring has elastic potential energy.
GPE = mass × g × height
Thermal (Heat) Energy
The energy associated with the movement of particles in a substance. Hotter objects have more thermal energy. The sun warms Australia through thermal energy transfer.
Light Energy
Energy carried by electromagnetic waves. Light from the sun travels 150 million km to reach Earth. Photovoltaic (solar) cells on Australian rooftops convert light to electrical energy.
Sound Energy
Energy carried by vibrations through a medium (solid, liquid, or gas). Sound cannot travel through a vacuum. A didgeridoo produces sound energy through vibrating air.
Electrical Energy
Energy carried by moving electric charges. Powers lights, appliances, and devices. Australia generates electrical energy from coal, gas, wind, and solar sources.
Chemical Energy
Energy stored in chemical bonds. Released during chemical reactions. Food contains chemical energy that your body converts to other forms. Petrol, batteries, and wood all store chemical energy.
Energy Transformations
Energy regularly transforms from one form to another. We use an arrow (→) to show the transformation. Energy is never lost — but some may be converted to less useful forms like heat.
Key Vocabulary
Kinetic Energy
The energy an object possesses due to its motion; depends on mass and speed.
Potential Energy
Stored energy due to an object's position or condition (gravitational, elastic, or chemical).
Energy Transformation
The conversion of energy from one form to another; total energy is always conserved.
Joule (J)
The SI unit of energy and work. Named after physicist James Prescott Joule.
Worked Examples
A toaster transforms what forms of energy?
Input: Electrical energy (from the power point).
Output: Thermal (heat) energy — to toast the bread. Also produces a small amount of light (the glowing element).
Transformation: Electrical → Thermal + Light
A student holds a ball 2 m above the ground, then drops it. Describe the energy transformation.
Held above ground: The ball has gravitational potential energy (stored due to its height).
During fall: GPE converts to kinetic energy — the ball speeds up as it falls.
On impact: Kinetic energy converts to sound and thermal energy.
Transformation: GPE → Kinetic → Sound + Thermal
Identify whether a 4 kg rock at rest on a 3 m shelf has kinetic or potential energy, and why.
The rock is at rest — it is not moving, so it has zero kinetic energy.
The rock is elevated — it is 3 m above the ground, so it has gravitational potential energy.
Answer: The rock has gravitational potential energy because of its position above the ground, not kinetic energy because it is stationary.
Knowledge Check
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Key Concepts Summary
- ✓ Energy is the ability to do work and is measured in joules (J).
- ✓ Seven main forms: kinetic, potential (gravitational, elastic), thermal, light, sound, electrical, chemical.
- ✓ The Law of Conservation of Energy: energy cannot be created or destroyed, only transformed.
- ✓ Kinetic energy is energy of motion; potential energy is stored energy.
- ✓ Energy transformations occur constantly — e.g. solar panels convert light to electrical energy.