E.1 Energy Forms and Transfers

UNIT SYLLABUS

Investigating different forms of energy, such as kinetic, potential, and chemical energy, and how they transform.

1 Key Formulas

Kinetic Energy

E_k = \frac{1}{2}mv^2

Gravitational Potential Energy

E_p = mgh

2 Exam Preparation & Topic Explanations

Energy Transfers and Sankey Diagrams

Energy transfers are the backbone of MYP energy questions. You must be able to identify useful and wasted (dissipated) energy for any device.

Sankey diagrams: The width of the arrows is proportional to the amount of energy. Useful energy goes right, wasted energy goes down.

Efficiency ( $\eta$ ): $\eta = \frac{\text{Useful output energy}}{\text{Total input energy}} \times 100\%$ , or $\eta = \frac{\text{Useful power output}}{\text{Total power input}} \times 100\%$ .

Common exam command: *Calculate the efficiency* → show working and express as a percentage.

Pro Exam Strategy

No real device is 100% efficient; always some energy is dissipated as thermal energy.
When analysing a roller coaster or pendulum, ignore friction unless stated – then use conservation of energy to find speeds or heights.
In ‘describe’ questions, always name the energy type at each stage (e.g., ‘chemical energy in the battery → electrical energy in the circuit → light + thermal energy in the bulb’).

Work and Power (Often Combined with Energy)

Work done = force × distance moved in the direction of the force ( $W = Fd$ ). 1 joule = 1 newton·metre.

Power = work done / time taken ( $P = W/t$ ) or energy transferred / time.

Many past papers combine work done against gravity ( $mgh$ ) with power calculations. Always check the time given and the mass.

Pro Exam Strategy

If a force is perpendicular to the movement (e.g., holding a book still), no work is done.
Use g = 10 m/s² unless 9.8 is specified – MYP often allows 10 for simplicity.
Write the formula, rearrange if needed, and always include units in the final answer.

3 MCQ Practice

Q1. Which of the following is a form of stored (potential) energy?

Light energy
Sound energy
Chemical energy
Kinetic energy

Q2. An object of mass 2 kg is raised to a height of 5 meters. What is its gravitational potential energy? (Take g = 9.8 m/s²)

$10\, J$
$49\, J$
$98\, J$
$196\, J$