ACT Science cheat sheet
ACT Science · Keep the key ideas within reach.
Science Content: Core Facts and Relationships
Density = mass / volume; an object floats in a fluid when its density is less than the fluid's density.
Speed = distance / time; acceleration is the change in velocity per unit time and is nonzero whenever direction or speed changes.
Newton's second law: net force = mass × acceleration; doubling mass at constant force halves acceleration.
Work = force × distance (force parallel to motion); power = work / time; energy is conserved but may change form.
Ideal gas law: PV = nRT; at constant temperature, pressure and volume are inversely proportional (Boyle's law).
In a neutral atom, protons equal electrons; atomic number = protons; mass number = protons + neutrons.
pH below 7 is acidic, above 7 is basic; each unit change represents a tenfold change in hydrogen ion concentration.
DNA bases pair A–T and G–C; in transcription DNA makes RNA with uracil replacing thymine.
Science Practices and Reasoning Skills
Identify the independent variable (manipulated), dependent variable (measured), and at least one controlled variable in each experiment.
A control group receives no treatment or a placebo; it establishes the baseline against which the experimental group is compared.
Correlation does not establish causation; only controlled manipulation of one variable supports a causal claim.
On a line graph, slope = change in y / change in x; slope units are (y units) per (x unit) and represent a rate.
Interpolation estimates values between plotted data points; extrapolation predicts beyond the data range and is less reliable.
Two sets of data conflict when the same condition produces different measured outcomes; identify which variable differed.
A hypothesis is supported, not proven; a single experiment can falsify but cannot confirm a hypothesis absolutely.
When comparing trials, larger sample size and repeated measurements increase confidence that a result is not due to chance.