Identifying Variables Kinds of Variables Independent Variable something

Identifying Variables

Kinds of Variables § Independent Variable – something that is changed by the scientist § What is tested § What is manipulated § Changed on purpose to see what may happen

Kinds of Variables § Dependent Variable – something that might be affected by the change in the independent variable § What is observed § What is measured § The data collected during the investigation

Kinds of Variables § Controlled Variable – a variable that is not changed § Also called constants § Allow for a “fair test”

The Bread Experiment § Let’s discuss variables, constants and controls using the bread experiment!

Problem/Question John watches his grandmother bake bread. He asks his grandmother what makes the bread rise. She explains that yeast releases a gas as it feeds on sugar.

Problem/Question John wonders if the amount of sugar used in the recipe will affect the size of the bread loaf?

Hypothesis The hypothesis is an educated guess about the relationship between the independent and dependent variables. Note: These variables will be defined in the next few slides.

Do you know the difference between the independent and dependent variables?

Independent Variable The independent, or manipulated variable, is a factor that’s intentionally varied by the experimenter. John is going to use 25 g. , 50 g. , 100 g. , 250 g. , 500 g. of sugar in his experiment.

Dependent Variable The dependent, or responding variable, is the factor that may change as a result of changes made in the independent variable. In this case, it would be the size of the loaf of bread.

Control Group In a scientific experiment, the control is the group that serves as the standard of comparison. The control group may be a “no treatment" or an “experimenter selected” group.

Control Group The control group is exposed to the same conditions as the experimental group, except for the variable being tested. All experiments should have a control group.

Control Group Because his grandmother always used 50 g. of sugar in her recipe, John is going to use that amount in his control group.

Constants John has to keep all other factors the same so that any observed changes in the bread can be attributed to the variation in the amount of sugar.

Constants The constants in an experiment are all the factors that the experimenter attempts to keep the same.

Can you think of some constants for this experiment?

Constants They might include: Other ingredients to the bread recipe, oven used, rise time, brand of ingredients, cooking time, type of pan used, air temperature and humidity where the bread was rising, oven temperature, age of the yeast…

Another Example:

Students of different ages were given the same jigsaw puzzle to put together. They were timed to see how long it took to finish the puzzle.

Identify the variables in this investigation.

What was the independent variable? § Ages of the students § Different ages were tested by the scientist

What was the dependent variable? § The time it to put the puzzle together § The time was observed and measured by the scientist

What was a controlled variable? § Same puzzle § All of the participants were tested with the same puzzle. § It would not have been a fair test if some had an easy 30 piece puzzle and some had a harder 500 piece puzzle.

Yet Another example:

An investigation was done with an electromagnetic system made from a battery and wire wrapped around a nail. Different sizes of nails were used. The number of paper clips the electromagnet could pick up was measured.

What are the variables in this investigation?

Independent variable: § Sizes of nails § These were changed by the scientist

Dependent variable: § Number of paper clips picked up § The number of paper clips observed and counted (measured)

Controlled variables: § Battery, wire, type of nail § None of these items were changed

Guess what? One more:

The higher the temperature of water, the faster an egg will boil.

§ Independent variable – temperature of water § Dependent variable – time to cook an egg § Controlled variable – type of egg and amount of water

Last one: (I promise)

The temperature of water was measured at different depths of a pond.

§ Independent variable – depth of the water § Dependent variable – temperature § Controlled variable – thermometer and pond

Designing Investigations

The greater the amount of soap in a soap and water mixture, the bigger a soap bubble can be blown. § Design an investigation to test this hypothesis. § Identify the variables § What exactly will be changed? How will it be changed? § What exactly will be measured? How will it be measured?

Variables § Independent § Amount of soap in Variable- soap water mixture § Dependent Variable- size of § Size of the bubble blown with different § Controlled Variable amounts of soap in -water and type of the water soap

The farther a ball drops, the higher it will bounce. § Design an investigation to test this hypothesis. § Identify the variables § What exactly will be changed? How will it be changed? § What exactly will be measured? How will it be measured?

Variables § Independent § The length of the Variable- length of fall, different fall for fall each trial § Dependent § The height of the Variable-height of bounce from the bounce different lengths of the fall ~ the higher § Controlled Variable the height of the - ball, surface, size fall the higher the of the ball bounce