Science Study Guide: Motion, Chemical Reactions, Genetics, Evolution, Waves & Light

Distance (scalar quantity)

The total path length an object travels, regardless of direction.

Displacement (vector quantity)

The straight-line distance and direction from an object's starting point to its finishing point.

Velocity-time graph gradient

Represents the acceleration of an object.

Area under a velocity-time graph

Represents the total distance travelled by an object.

Newton's First Law of Motion

An object remains at rest or continues moving at a constant velocity unless acted upon by an unbalanced net force.

Newton's Second Law equation

$$F = ma$$

Newton's Third Law of Motion

For every action force, there is an equal and opposite reaction force.

Combustion of methane equation

$$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$$

Law of Conservation of Mass

In a closed system, the total mass of reactants equals the total mass of products because atoms are rearranged, not created or destroyed.

Atomic radius trend across a period

Decreases from left to right because an increasing nuclear charge pulls the electron shell tighter toward the nucleus.

Atomic radius trend down a group

Increases because each additional row adds an electron shell, moving outer electrons further from the nucleus.

Group 1 metal reactivity trend

Increases down the group because the outer electron is further from the nucleus and lost more easily.

Mitosis vs. Meiosis output

Mitosis produces two genetically identical diploid cells; meiosis produces four genetically different haploid gametes.

DNA to mRNA base pairing rules

Adenine ($A$) pairs with Uracil ($U$), Thymine ($T$) pairs with Adenine ($A$), and Cytosine ($C$) pairs with Guanine ($G$).

Pedigree chart rule for recessive traits

If two unaffected parents produce an affected offspring, the trait is recessive and both parents are heterozygous carriers.

Divergent evolution

When populations of a single ancestral species split and evolve into different species due to different selection pressures.

Convergent evolution

When species from different ancestries independently evolve similar traits due to similar environmental pressures.

Homologous vs. Analogous structures

Homologous structures share common evolutionary ancestry (e.g., pentadactyl limb); analogous structures share similar function without common ancestry (e.g., bird and insect wings).

Transverse vs. Longitudinal waves

In transverse waves, particle vibration is perpendicular to energy transfer; in longitudinal waves, particle vibration is parallel to energy transfer.

Wave speed equation

$$v = f \times \lambda$$

Independent variable

The variable that is deliberately changed in an experiment.

Dependent variable

The variable that is measured in an experiment to test the effect of changing the independent variable.

Experimental validity vs. Reliability

Validity assesses whether an experiment properly tests the hypothesis with controlled variables; reliability assesses consistency of results across repeated trials.