Independent Variable
What is the independent variable in an experiment?
The one thing in an experiment that is changed by the scientist.
What is the dependent variable in an experiment?
The thing that is measured to see the effect of the independent variable.
What is a control group in an experiment?
A group that stays the same so we can compare results.
What is a hypothesis?
A guess about what will happen in an experiment.
What do scientists do at the end of an experiment?
They look at their data and decide what it means.
In an experiment testing the reaction different amounts of mentos have with coke, what is the independent variable?
The different amounts of mentos
In an experiment testing the reaction different amounts of mentos have with coke, what is the dependent variable?
The reaction
Why do scientists use a control group?
To make sure that what we are testing is really causing the change.
What is the format for writing a hypothesis.
If ... then ... because ...
If your hypothesis was wrong, what should you do?
That’s okay! Scientists learn from every experiment. You should try to understand why your hypothesis was wrong and start a new experiment test your new ideas.
A student is testing which type of paper towel absorbs the most water. What is the independent variable?
The brand/type of paper towel.
A scientist tests how different fertilizers affect how many tomatoes grow on a plant. What is the dependent variable?
The number of tomatoes that grow.
A scientist is testing the reaction different amounts of mentos have with coke. What would be a good control group?
0 mentos
Bonus: why is this a good control?
A student thinks a reaction will be larger when you add more mentos to coke. What is their hypothesis?
If you add more Mentos to the Coke, then the reaction will be bigger because the extra Mentos will make more bubbles.
A student tests if fertilizer helps plants grow taller. The plants with fertilizer grew 5 inches taller than the ones without it. What does this tell us?
Fertilizer helps plants grow taller.
Why is it important to only have one independent variable in an experiment?
So we know that any change in results is caused by that one thing and not something else.
How can you tell the difference between an independent and a dependent variable?
The independent variable is what you change, the dependent variable is what you measure.
If you are testing how different drinks stain teeth, what would be a good control group?
A tooth soaked in water.
True or False: A hypothesis must always be correct.
False! It’s okay if your guess is wrong. That’s how science works!
A class tests how different drinks stain teeth. After one week, they find that soda stains the most, followed by coffee, then juice, and finally water. What is their conclusion?
Soda stains teeth the most, while water does not stain at all.
Think of an experiment you could do with water and temperature. What would be a good independent variable to test?
Variety of answers
Ex: In an experiment changing water temperature to see how fast sugar dissolves, the temperature is the independent variable.
Bonus: what is the dependent variable?
Think of an experiment using ice cubes. What would be a good dependent variable to measure?
Variety of answers
Ex: In an experiment testing how long an ice cube takes to melt at different temperatures, the dependent variable is the length of time for the ice cube to melt.
Bonus: what is the independent variable?
A student wants to see if a special shoe makes people run faster. What would be the control group in this experiment?
People running in their regular shoes.
Bonus: What would be the independent and dependent variables?
A class wants to test if the type of water (fresh, salt, or sugar) affects how fast an ice cube melts. What is a good hypothesis?
If the type of water changes, then the ice cube will melt at different speeds, because ...
A scientist measures how fast ice melts in different temperatures. They find that ice melts fastest at 90°F, slower at 70°F, and hardly melts at all at 32°F. What is their conclusion?
Ice melts faster in warmer temperatures.