The moving parts of a machine are lubricated with oil.
Why does this reduce unwanted energy transfer?
It increases friction, so the parts grip each other more firmly
It cools the parts, so energy is transferred to them from the air
It insulates the parts, so less energy is transferred by radiation
It reduces friction, so less energy is dissipated to thermal stores
50 exam-style questions on OCR GCSE Physics 7.2 Power and efficiency, covering 7.2.1 Dissipation of energy, 7.2.2 Energy transfers in domestic devices, 7.2.3 Power ratings of domestic appliances, 7.2.4 Efficiency of energy transfers, 7.2.5 Ways to increase efficiency, 7.2.6 Reducing unwanted energy transfers, and 7.2.7 Thermal conductivity and the cooling of buildings. Each one has a worked solution and a mark scheme showing where the marks go.