designing an Experiment

A variable is something that changes.

6 components of an experiment independent variable dependent variable constants control group experimental group repeated trials

the variable that is changed on purpose by the experimenter independent variable the variable that is changed on purpose by the experimenter aka cause, stimulus, reason, manipulated variable, etc.

the variable that changes in response to the independent variable aka effect(s), result(s), responding variable, etc.

all the factors which are NOT allowed to change during the experiment constants all the factors which are NOT allowed to change during the experiment

the group (standard) to which everything is compared control group the group (standard) to which everything is compared

the group(s) being tested using the independent variable experimental group the group(s) being tested using the independent variable Each test group has only one factor different from the other test groups: the independent variable.

the number of times the experiment is repeated repeated trials the number of times the experiment is repeated An experiment should be carried out many times to produce accurate/ repeatable results

Before carrying out an experiment, you MUST identify your independent variable, constants and dependent variable.

6 drops fertilizer 4 drops fertilizer 2 drops fertilizer no fertilizer

EXPERIMENTAL GROUP CONTROL 2 drops fertilizer 4 drops fertilizer What is this called? What are these called? CONTROL EXPERIMENTAL GROUP no fertilizer

What are these called? CONSTANTS

dependent variable What is this called? The plant growth that you observe here can be called . . .  the results (of adding fertilizer)  the response (to adding fertilizer) dependent variable  the effects (of adding fertilizer) 2 4 6

forming a hypothesis

A good hypothesis: - Is a statement (NOT a question) - Is written in clear and simple language - Relates the independent and dependent variables Is testable Can be written in several ways (including if, then statement)

Write a hypothesis for the plant experiment in the box in your notes.

Good! Warm water will dissolve more salt than cold water. Good or Bad Hypothesis? Warm water will dissolve more salt than cold water. Good! What is another way this hypothesis can be written?

Bad Will fertilizer make my lawn grow more? Good or Bad Hypothesis? Will fertilizer make my lawn grow more? Bad How can you make this a good hypothesis?

recording and displaying Results

iv constants dv fertilizer plant growth 0 drops Results from your experimentation should be recorded in a carefully constructed data table. 2 drops 4 drops 6 drops

A data table has at least 2 columns of information. iv constants dv fertilizer plant growth 0 drops 1 cm 2 drops 1.5 cm 4 drops 1.5 cm 6 drops 3 cm A data table has at least 2 columns of information.

Independent variable data is always. (a) recorded in the left column Independent variable data is always (a) recorded in the left column (b) recorded BEFORE experimentation fertilizer 0 drops 2 drops 4 drops 6 drops IV

fertilizer fertilizer (drops) 0 drops 2 4 6 2 drops 4 drops 6 drops

Dependent variable data is always. (a) recorded in the right column Dependent variable data is always (a) recorded in the right column (b) recorded DURING experimentation plant growth 1 cm 1.5 cm 3 cm fertilizer (drops) DV 2 4 6

plant growth 1 cm 2 4 6 1 1.5 3 1.5 cm 1.5 cm 3 cm fertilizer (drops) 2 4 6 1 1.5 3 1.5 cm 1.5 cm 3 cm

Choose an appropriate title for the data table. Effect of Fertilizer on Plants Growth fertilizer (drops) plant growth (cm) 2 4 6 1 1.5 3

Effect of Fertilizer on Plants Data from a correctly constructed data table can be displayed in a graph. fertilizer (drops) 2 4 6 plant growth (cm) 1 1.5 3 Effect of Fertilizer on Plants

IV data is plotted on the X axis. DV data is plotted on the Y axis. fertilizer (drops) 2 4 6 plant growth (cm) 1 1.5 3 Effect of Fertilizer on Plants 1.0 2.0 1.5 .5 2.5 3.0 plant growth (cm) 2 4 6 fertilizer (drops)

The title of the data table is also the title of the graph. fertilizer (drops) 2 4 6 plant growth (cm) 1 1.5 3 Effect of Fertilizer on Plants Effect of Fertilizer on Plants 1.0 2.0 1.5 .5 2.5 3.0 plant growth (cm) 2 4 6 fertilizer (drops)