THREE KINDS OF VARIABLES

EQ: What are the most effective ways to carry out a scientific inquiry?

Sometimes in science, events are so big (like the explosion of a volcano), or so small (like the movement of Euglena) or so distant (like the movement of a star) that it is impossible for our brains to understand them in their entirety.

Variables

Variables The scientific

approach to understanding these events is a process that breaks down complex events into smaller pieces that can be studied and understood.

These smaller parts are called variables.

Variables are factors, conditions, and/or relationships that can change or be changed in an event or system

Variables

Three Kinds of Variables In a scientific

investigation there are 3 kinds of variables:

Independent Dependent Controlled

Independent Variable This is the factor or

condition that is intentionally changed.

May only have one in a valid experiment!!!!

EX: A study was done to find if different tire treads affect the breaking distance of a car.

I Variable: tire treads

This is the factor or condition that might be affected as a result of the change.

EX: A study was done to find if different tire treads affect the breaking distance of a car.

D Variable: breaking distance

Dependent Variable

Controlled Variable These are the variables that

should not change.

Not necessarily mentioned in a description or hypothesis.

EX: A study was done to find if different tire treads affect the breaking distance of a car

Controls: same car, new brake pads each time, same speed, same place applying brakes…

Two groups of students were tested to compare their speed working math problems. One group was given calculators, the other was not Each group was given the same math problems.

I Variable: D Variable: Controls:

Practice 1: T-P-S

Independent Variable: Use of calculators

Dependent Variable: Speed computing the problems

Controls: same problems, same kids…

Practice 1

Students of different ages were given the same puzzle to complete. The puzzle assembly time was measured.

I Variable:

D Variable

Controls:

Practice 2: T-P-S

Independent Variable: Age of students

Dependent Variable: Speed of puzzle assembly

Controls: same puzzle

Practice 2

Writing a HypothesisEQ: What are the most effective ways to carry out a scientific inquiry?

A hypothesis is a tentative statement that proposes a possible explanation to some phenomenon or event.

A useful hypothesis is a testable statement which may include a prediction.

What is a real hypothesis?

The key word is testable.

That is, you will perform a test of how two variables might be related.

This is when you are doing a real experiment. You are testing variables.

When are hypotheses used?

When are hypotheses used? Usually, a hypothesis is

based on some previous observations.

Such as noticing that in November many trees undergo color changes in their leaves and the average daily temperatures are dropping.

Are these two events connected?

How?

Cooler days in November may cause the leaves on the trees to change color

*Dawn dish soap may blow bigger bubbles

All of these are examples of hypotheses because they use the tentative word "may.".

How are hypotheses written?

However, their form is not particularly useful. Using the word may does not suggest how you would go about proving it.

If these statements had not been written carefully, they may not have even been hypotheses at all.

For example, if we say "Trees will change color when it gets cold.“, we are making a prediction.

Or if we write, "Dawn dish soap will blow bigger bubbles”, this could be a conclusion.

One way to prevent making such easy mistakes is to formalize the form of the hypothesis.

How are hypotheses written?

If leaf color change is related to temperature , then exposing plants to low temperatures will result in changes in leaf color.

Notice that these statements contain the words if and then.

They are necessary in a formalized hypothesis.

If you always ask yourself that if one thing is related to another, then you should be able to test it.

Formalized Hypotheses

Formalized hypotheses contain two variables.

One is independent and the other is

dependent.

The independent variable is the one you, the scientist control

The dependent variable is the one that you observe and/or measure the results.

Formalized Hypotheses

But not all if-then statements are hypotheses.

For example, "If I play the lottery, then I will get rich."

This is a simple prediction.

In a formalized hypothesis, a tentative relationship is stated. For example, if the frequency of winning is related to frequency of buying lottery tickets.

Formalized Hypotheses

A study was done to find if different tire treads affect the breaking distance of a car.

Independent:

Dependent

Hypothesis --- Make sure a relationship between the I and D variables is clear

Practice: T-P-S