Praxis Middle School Science cheat sheet

Density = mass/volume; an object floats in a fluid when its average density is less than the fluid's density.

Newton's second law: F = ma; weight = mg where g ≈ 9.8 m/s² near Earth's surface.

Speed = distance/time; acceleration = change in velocity/change in time; velocity is a vector, speed is a scalar.

Kinetic energy = ½mv²; gravitational potential energy = mgh; energy is conserved but transforms between forms.

Atomic number = protons; mass number = protons + neutrons; isotopes differ in neutron count, ions differ in electron count.

pH scale: below 7 acidic, 7 neutral, above 7 basic; each unit represents a tenfold change in hydrogen ion concentration.

Photosynthesis: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂; cellular respiration is approximately the reverse.

Plate tectonics: divergent boundaries create new crust, convergent boundaries produce subduction or mountains, transform boundaries cause faulting.

Earth's rock types: igneous forms from cooling magma/lava, sedimentary from compaction of deposits, metamorphic from heat and pressure.

Independent variable is manipulated by the researcher; dependent variable is measured; controlled variables are held constant.

A valid experiment includes a control group to isolate the effect of the independent variable.

Hypothesis must be testable and falsifiable; a prediction states an expected outcome under specified conditions.

Accuracy is closeness to the true value; precision is repeatability of measurements; random error reduces precision, systematic error reduces accuracy.

Significant figures: nonzero digits count, captive zeros count, leading zeros do not, trailing zeros count only with a decimal point.

Scientific notation: a × 10ⁿ where 1 ≤ a < 10; positive n for large numbers, negative n for small numbers.

Correlation does not imply causation; confounding variables can produce spurious associations.

Mean, median, and mode describe central tendency; range and standard deviation describe spread.

A scientific theory is a well-supported explanation repeatedly tested; a law describes a consistent relationship, often mathematically.