Scientific Inquiry and Skills - Formulating Hypotheses and Variables

A student wants to investigate how the concentration of salt affects the boiling point of water. Identify the variables and formulate a hypothesis.

Independent Variable ($IV$): Concentration of $NaCl$ (g/L). Dependent Variable ($DV$): Boiling point temperature ($^{\circ}C$). Control Variables: Volume of $H_2O$, atmospheric pressure, and type of heating element. Hypothesis: If the concentration of $NaCl$ increases, then the boiling point of the solution will increase because dissolved solutes elevate the boiling point of a solvent.

The student changes the salt amount ($IV$) and measures the temperature change ($DV$). The scientific reasoning relies on the principle of boiling point elevation.

In an experiment measuring the rate of photosynthesis, a student counts $O_2$ bubbles released by a plant at different distances from a light source. State the variables.

$IV$: Light intensity (calculated as $\frac{1}{d^2}$ where $d$ is distance). $DV$: Rate of photosynthesis (measured as bubbles per minute). Controls: Temperature of the water, amount of $CO_2$ available (using $NaHCO_3$), and the species of plant.

Light intensity is the factor being manipulated. The number of $O_2$ bubbles is the quantitative data collected to represent the biological process.

Write a hypothesis for an experiment testing the effect of mass ($m$) on the acceleration ($a$) of a trolley when a constant force ($F$) is applied.

Hypothesis: If the mass ($m$) of the trolley is increased, then the acceleration ($a$) will decrease because, according to Newton's Second Law ($F = ma$), acceleration is inversely proportional to mass ($a \propto \frac{1}{m}$) when force is constant.

This hypothesis uses the required 'If... then... because' format and references a specific mathematical relationship ($a = \frac{F}{m}$).