PHYSICS · Stage 9 · Chapter 15: The Earth in Space (Universe and Stars)
Physics Stage 9 Comprehensive Review
5 min read 5 parts Lesson 6 of 6
Lesson summary
Physics Stage 9 Comprehensive Review — Alhussan International Academy — Physics (Stages 7–9) notes: Summarise Stage 9 ideas on density, cooling by evaporation, energy transfer, sound and circuits.Floating — An object floats on a liquid if its density is less than the liquid's.Sin…
- Typical values
- Shade and hats
- Dark, tight clothing
- Conduction
- Convection
- Efficiency
Section 1 of 5Comparing densities
- Floating
- An object floats on a liquid if its density is less than the liquid's.
- Sinking
- An object sinks in a liquid if its density is more than the liquid's.
- Ordering
- An object that sinks in oil but floats on water has a density between the oil's and the water's.
- Typical values
- Cooking oil is about 0.9 g/cm³ and water 1.0 g/cm³.
Section 2 of 5Staying cool in hot conditions
- Evaporation
- Sweat evaporates from the skin, taking energy from the body.
- Clothing
- Pale, loose clothing reflects infrared from the Sun and allows air to circulate.
- Shade and hats
- They reduce the radiation absorbed.
- Drinking
- Water replaces lost fluid.
- Dark, tight clothing
- It absorbs more infrared and traps heat.
Section 3 of 5Energy transfer and efficiency
- Conduction
- Energy passes through solids.
- Convection
- Fluids circulate as warm fluid rises.
- Radiation
- Energy travels as infrared waves.
- Efficiency
- Efficiency = × 100%.
- (useful energy out ÷ total energy in)
- Efficiency = × 100%.
- Conservation
- Total energy is conserved, but wasted energy is dissipated into the surroundings.
Section 4 of 5Sound
- Pitch
- Frequency in hertz determines pitch.
- Loudness
- Amplitude determines loudness.
- Decibels
- A 10 dB increase means 10 times the intensity.
- Interference
- Waves in step add up and waves out of step cancel.
Section 5 of 5Circuits
| Rule | Series | Parallel |
|---|---|---|
| Current | Same everywhere | Branch currents add up |
| Voltage | Voltages add up to the battery voltage | Same across each branch |
- Resistance
- R = V ÷ I.
- Energy in kWh
- Energy = power in kW × time in hours.
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