HomePhysicsP4: Energy Resources and Energy TransferP4.1 Forms of Energy and Energy Conservation

P4: Energy Resources and Energy Transfer

P4.1 Forms of Energy and Energy ConservationP4.2 Work and Power
P4: Energy Resources and Energy Transfer

Forms of Energy and Energy Conservation

Understand different forms of energy and how they transform while total energy remains constant

Forms of energy

Energy Transformations

Energy changes form but is never lost

Forms of Energy
Understanding the eight main types

Energy exists in various forms, each with specific characteristics:

  • Kinetic energy: Energy of moving objects (Ek = ½mv²)
  • Gravitational potential energy: Energy stored due to height (Ep = mgh)
  • Elastic potential energy: Energy in stretched springs (Ep = ½kx²)
  • Thermal energy: Internal energy of particles, increases with temperature
  • Chemical energy: Stored in bonds, released during reactions
  • Electrical energy: Energy from moving charges (P = VI)
  • Nuclear energy: Stored in atomic nuclei, released in fission/fusion
  • Electromagnetic/light energy: Energy carried by electromagnetic waves
Law of Conservation of Energy
Energy cannot be created or destroyed

The law of conservation of energy states that in an isolated system, the total energy remains constant. Energy can transform from one form to another, but it is never created or destroyed.

Total Energy Before = Total Energy After

For example, when a ball is dropped, gravitational potential energy converts to kinetic energy. At impact, kinetic energy transforms into thermal energy and sound. The total energy stays the same throughout.

Energy Transfers and Dissipation
How energy moves between forms

Energy transfer occurs when energy changes from one form to another. Common examples include:

  • Car engine: chemical (fuel) → kinetic (motion) + thermal (heat)
  • Light bulb: electrical → light + thermal
  • Solar panel: light → electrical

Energy dissipation refers to useful energy being lost to the surroundings, usually as heat. This is inevitable due to friction and resistance. Dissipated energy increases entropy (disorder) and cannot easily be recovered.

Efficiency
Measuring useful energy output

Efficiency measures how much useful energy is transferred compared to the total input:

Efficiency = (Useful Energy Out ÷ Total Energy In) × 100%

Efficiency is always less than 100% because some energy is always dissipated as heat due to friction, air resistance, or electrical resistance.

Example

A motor uses 500 J of electrical energy and produces 400 J of kinetic energy.
Efficiency = (400 ÷ 500) × 100% = 80%
The remaining 100 J is dissipated as heat.

Interactive Energy Transformer
Select input and output energy types to see real-world examples and typical efficiencies

From (Input Energy):

To (Output Energy):

Chemical→Kinetic

Car engine converts fuel into motion

Typical efficiency: ~25%

Energy Flow (Sankey Diagram)

Input:
100 J Chemical
Useful Output:
25 J Kinetic
Wasted (Heat):
75 J

Efficiency = (Useful Energy Out ÷ Total Energy In) × 100%

= (25 J ÷ 100 J) × 100% = 25%

Key Principle: Energy is always conserved but never 100% efficiently transferred. Some energy is always lost as heat to the surroundings.

Key Terms Flashcards
Click the card to reveal the definition

Kinetic Energy

Card 1 of 8
Worked Example
Energy transformations in a bouncing ball

Question:

A ball with mass 0.5 kg is dropped from a height of 2 m. Identify all the energy forms and calculate the gravitational potential energy at the start (g = 10 N/kg).

Answer:

Energy forms:
- At top: Gravitational potential energy (Ep)
- Falling: Ep converts to kinetic energy (Ek)
- At ground: All energy is kinetic (just before impact)
- After bounce: Ek converts back to Ep, plus some thermal/sound

Calculation:
Ep = mgh = 0.5 kg × 10 N/kg × 2 m = 10 J

At the bottom, all 10 J is kinetic. After bouncing to 1.5 m height, some energy has been dissipated as heat and sound.

Check Your Understanding
Question 1 of 6

Which formula calculates kinetic energy?