Experimental Design

What are the three types of variables in any experiment?

• Independent variable, dependent variable, controlled variable
• Variable A, variable B, variable C
• Primary variable, secondary variable, tertiary variable
• Experimental variable, random variable, fixed variable

A student adds sugar to a cup of iced tea and a cup of hot tea. She notices that the amount of sugar that dissolves in each cup is different. More sugar dissolves in the hot tea than in the iced tea. She thinks this has something to do with the temperature of the tea. She wants to design an experiment to see if she is correct.

Identify two variables that should be controlled variables in an experiment to test this hypothesis.

• Amount of sugar added, type of tea used
• Size of the cup
• Type of sugar used
• Temperature of the room

A student adds sugar to a cup of iced tea and a cup of hot tea. She notices that the amount of sugar that dissolves in each cup is different. More sugar dissolves in the hot tea than in the iced tea. She thinks this has something to do with the temperature of the tea. She wants to design an experiment to see if she is correct.

Did more or less sugar dissolve when the student had hotter tea?

• More

• Less

A student adds sugar to a cup of iced tea and a cup of hot tea. She notices that the amount of sugar that dissolves in each cup is different. More sugar dissolves in the hot tea than in the iced tea. She thinks this has something to do with the temperature of the tea. She wants to design an experiment to see if she is correct.

Write a hypothesis based on the student's observations.

Shamia sees that the tomato plants on the left side of her garden grow tall but the tomato plants on the right side of her garden are shorter. She notices that the sun shines onto the left side of her garden, but the right side of her garden is in the shade.

Write a hypothesis based on Shamia's observations.

Brett hypotheses that plants grow more under normal sunlight (white light) than under red light or blue light. He designs the following experiment:

If Brett's hypothesis is correct, what predictions would you make about which plants will grow the most?

Brett hypotheses that plants grow more under normal sunlight (white light) than under red light or blue light. He designs the following experiment:

What is the control group in this experiment?

Destiny wants to measure whether Pepsi or orange juice causes teeth to decay more. She uses some teeth her science teacher has and drops one in a glass of Pepsi and one in a glass of orange juice. What should she do for her control group?

• Put a tooth in milk, because milk is healthy

• Put a tooth in coke, to see if it has more sugar than Pepsi

• Put a tooth in water, because water has no sugar

Jake learned in class that hand sanitizers kill germs. He wants to know whether some hand sanitizers are better at killing germs. He puts three different hand sanitizers on germs and measures how many germs are left. What should he do for a control group?

What should Jake do for a control group?

• test another hand sanitizer

• nothing, he is testing enough hand sanitizers

• measure the growth of germs with no hand sanitizer on them

Saltwater plants of the same species were grown in soil in separate containers with 1 liter of water. Different amounts of salt were put in each container as shown in the diagrams.

Which one is the control group in this experiment?

• the container with no salt

• the container with 5 grams of salt

• the container with 10 grams of salt

• the container with 20 grams of salt