Saga Public High School Entrance Examination - Science cheat sheet

Newton's second law: net force = mass × acceleration (F = ma); acceleration is in the direction of the net force and is zero when forces balance.

Weight = mass × gravitational acceleration (W = mg); on Earth g is about 9.8 N/kg, so 1 kg weighs about 9.8 N.

Speed = distance ÷ time; velocity adds direction, and acceleration = change in velocity ÷ time taken.

For a lever in balance: effort × effort arm = load × load arm; for a pulley system the mechanical advantage equals the number of supporting rope segments.

Work = force × distance moved in the direction of the force (W = Fd); power = work ÷ time, measured in watts.

Kinetic energy = ½mv²; gravitational potential energy = mgh; in a closed system total mechanical energy is conserved when friction is neglected.

Ohm's law: voltage = current × resistance (V = IR); resistors in series add (R = R₁ + R₂), and in parallel 1/R = 1/R₁ + 1/R₂.

Electric power = voltage × current (P = VI); energy used = power × time, so a 1000 W appliance run for 2 hours uses 2 kWh.

Wave speed = frequency × wavelength (v = fλ); frequency is set by the source, and when a wave enters a new medium its speed and wavelength change but frequency stays the same.

A pure substance has a fixed composition; a mixture can be separated by physical means such as filtration, distillation, or evaporation.

In a chemical change new substances form and the change is usually hard to reverse; in a physical change no new substance forms.

Kinetic particle theory: particles are in constant motion, and heating increases their average speed, which raises the rate of diffusion.

Atomic structure: protons (+) and neutrons (neutral) sit in the nucleus, electrons (−) occupy shells; atoms of the same element have the same proton number.

An ion is an atom or group that has gained or lost electrons: metals lose electrons to form positive ions, non-metals gain electrons to form negative ions.

Acids release hydrogen ions (H⁺) in water; alkalis release hydroxide ions (OH⁻); pH below 7 is acidic, 7 is neutral, above 7 is alkaline.

Neutralisation: acid + base → salt + water, for example HCl + NaOH → NaCl + H₂O.

A chemical equation must be balanced so that the number of atoms of each element is the same on both sides, because mass is conserved.

Reaction rate increases with higher temperature, higher concentration, smaller particle size (greater surface area), or a catalyst.

Plant cells have a cell wall, chloroplasts, and a large permanent vacuole; animal cells lack these but both have a nucleus, cytoplasm, and cell membrane.

Mitochondria release energy by respiration; ribosomes build proteins; the nucleus contains DNA and controls the cell.

Photosynthesis: carbon dioxide + water → glucose + oxygen, using light energy absorbed by chlorophyll in chloroplasts.

Aerobic respiration: glucose + oxygen → carbon dioxide + water + energy; anaerobic respiration in muscle releases energy without oxygen and produces lactic acid.

Mitosis produces genetically identical cells for growth and repair; meiosis produces gametes with half the chromosome number, restoring the full number at fertilisation.

In a genetic cross, a dominant allele is expressed even when only one copy is present; a recessive trait appears only when both alleles are recessive.

Natural selection: individuals with variations better suited to the environment survive and reproduce more, so those alleles become more common over generations.

In a food chain, arrows show the direction of energy flow; only about 10% of energy passes to the next trophic level, the rest is lost mainly as heat.

Decomposers break down dead material and return nutrients such as carbon and nitrogen to the soil for producers to reuse.

Earth's rotation on its axis (about 24 hours) causes day and night; its revolution around the Sun (about 365.25 days) plus axial tilt causes the seasons.

The Moon orbits Earth in about 28 days; the phases we see depend on the changing angle between Earth, Moon, and Sun, not on Earth's shadow.

A solar eclipse occurs when the Moon passes between Earth and the Sun; a lunar eclipse occurs when Earth's shadow falls on the Moon.

Rock types: igneous rock forms from cooled magma or lava, sedimentary rock from compacted layers of sediment, and metamorphic rock from heat and pressure on existing rock.

The rock cycle links the three rock types through melting, cooling, weathering, erosion, deposition, and metamorphism.

Weather is the short-term state of the atmosphere; climate is the long-term average pattern of weather for a region.

Air pressure falls with altitude; wind blows from high-pressure to low-pressure areas, and the greater the pressure difference the stronger the wind.

Warm, moist air rising and cooling causes condensation into clouds and often precipitation; descending air tends to bring clear, dry weather.

Earth's internal structure: a solid inner core, liquid outer core, mantle, and thin crust; movement in the mantle drives plate motion.