Experiments NC SCOS Obj. 1.2

Controlled = Good! Controlled Experiment – only ONE variable is tested (or changed by experimenter) at a time WHY? So you can tell what variable is causing the observed results

Variable – any factor that can change from trial to trial –vary = change –Ex. Height of dropper, type of dropper, side of penny, etc.

Parts of an Experiment 1.Independent (or manipulated) variable -- factor that is changed by experimenter -- changed 1 st, on x-axis 2. Dependent (or responding) variable -- factor that is measured to show results -- changes 2 nd, on y-axis Dependent Independent

For any research question: How does (independent) affect (dependent)? A. How does sunlight affect plant growth? B. How does the distance between earth and a star affect the star’s brightness? C. How does seafloor topography affect wave height? I.V D.V. I.V D.V.

3. Constants (or controlled variables) – factors that are kept the same 4. Control group – a group or trial that does not receive any treatment -- a standard for comparison -- the “normal” group

Practice Sally decides to test how amount of fertilizer affects tomato production. She grows two tomato plants nearby in her garden so they have the same soil, water, and sunlight. She applies fertilizer to plant A and none to plant B. Each week, she measures the number of tomatoes each plant produces. I.V. D.V. Control group Constants