Why do we conduct

experiments?

Scientists use experiments to search for cause and effectrelationships in nature.

Design of the experiment

scientists design an experiment so that the changes to ONE item causes something else to vary in a predictable wayHas 2 groups Control group Experimental group

What are these changing qualities called?

variables

this is any factor, trait, or condition that can exist in differing amounts or types

Control Group

Used to see what happens when nothing is changed contains CONTROLLED VARIABLES that are kept the same from group to group or trial to trial

Experimental Group

Can be more than one group, changing the same variable Only ONE variable is changed, this is called the INDEPENDENT VARIABLE (aka: manipulated variable)This is used to check for a RESPONSE (“the cause” or “what you are changing”)

The Effect

The DEPENDENT VARIABLE Outcome of the changed variable What changed because of what you

changed in the experimental group

Reproducible Results

To be considered VALID, a successful experiment must be REPLICABLE & shows definite CAUSE & EFFECT

Published work in science journals so that other scientists can try their experiments

http://www.sciencemag.org/journals http://www.aaas.org/science-journals

ExperimentProblem: “Does caffeine increase the heart rate of an earthworm?” The heart rate is measured by looking at the earthworm under microscopes. In one group, the heart rate is measured to be 50 bpm (beats per minute). In another group, 3 drops of caffeine are given to the earthworm and the heart rate is measured at 68 bpm.

Controlled Experiment Groups

Controlled Variable(What I Keep the Same)

Independent Variable(What I Change)

Dependent Variable (What I Observe)

Possible Errors

Experiment

Problem: How does music effect the growth of tomatoes?The student has 2 tmato plants, Plant A and Plant B, the he grows by a window and gives the same amount of water. Plant A is exposed to classical music using headphones attached to the soil. Throughout the growth period, the student counts the number of tomatoes produced by each plant.Results: Plant A = 35 tomatoes Plant B = 55 tomatoes

Controlled Experiment Groups

Controlled Variable(What I Keep the Same)

Independent Variable(What I Change)

Dependent Variable (What I Observe)

Possible Errors