independent+and+dependent+variables

Most science investigations require a controlled experiment. A __ controlled experiment __ is an experiment in which only one variable is tested at a time.

Investigations will often refer to both an independent and dependent variable. Independent and dependent variables are related to one another.
 * The __**independent (or manipulated) variable**__ is the variable that you, the experimenter, change or manipulate intentionally.
 * __**Dependent (or responding) variable**__ is the variable that changes when the independent variable changes. The dependent variable depends on the outcome of the independent variable.

With each of these experiments, it is very important to control the experiment.

Question 1: You ONLY want to test the TYPE of liquid. Imagine you watered one plant with water every day and another plant with vinegar every other day. If you found the plant given vinegar grew less tall, you wouldn't know if it is because of the type of liquid or the frequency of which you watered the plant. There are TOO MANY VARIABLES. Kids will relate to this being a "fair" comparison or not. In this investigation, the following variables must be kept the same between the two plants: the type of plant, size of container, amount of sunlight each day, temperature, amount of liquid, how frequently the plant is watered… etc. These variables that are kept the same are called controlled variables.

Of course, we cannot control everything in an experiment. We may have the same types of plant, but one seed was not as robust. Perhaps when we planted the seed, one seed was slightly deeper in the pot than the other. These types of control mishaps constitute "experimental error."

- from Ms. Mytko's Curriki page

example from the Paper Towel Challege:

IDEA #1 Question: **__Which brand of paper towel is most absorbent?__**


 * Independent Variable ** (the variable I set up): **__The brand of paper towel__**


 * Dependent Variable ** (what I will measure): **__milliliters of water absorbed__**

Things I need to control: **Size of paper towel, how quickly I pour the water, temperature of the water…**

Brief idea for experiment / presentation: **Hold up paper towel. Start with 50 ml of water in a graduated cylinder. Pour water on paper towel until water drips through. Measure how much water is left in the grad cyl and subtract from 50 ml to find the amount absorbed.**

Any links with more background information:
 * How do paper towels absorb water - small sugar-like molecules (cellulose) attract water.
 * Consumer Reports Paper Towel Buying Guide