Designing Experiments,

part 2September 3, 2015(1.3 in your books)

Meme Momentclue

Scientist of the Day

Neil deGrasse Tyson• Went to the Hayden

Planetarium when he was 9 and suddenly wanted to be an astronomer

• Started lecturing on astronomy at 15

• Carl Sagan invited him over• Wrestling, rowing, and

dance at Harvard• Started running the same

planetarium• Took over Carl Sagan’s

show

Controlled Experiments, part 2

• A controlled experiment is one where only 1 variable is changed at a time

• This makes it easy to see cause & effect• When you change 1 variable, you’re hoping to

see a change in the result

Independent variable: The variable you change on purpose

Dependent variable: The change you see as a result of changing the independent variable

VocabularyManipulated variable: independent variable

Responding variable: dependent variable

Repeated trial: repeating the experiment several times to get better data through averages. Also called rigor.

Replication: letting someone else repeat your experiment to check for biases

7th and 8th grade

Features of a Good Experiment

1. Free of biaso Personalo Culturalo Experimental

2. Controlled experimento Test one variable at a time to see what actually changes

the result

3. Repeated trialso Always better to do it more than once – that way you

can take averages

4. Replicationo Let other people repeat the experiment to see if they get

the same resulto Helps check for biases

Scientific Theories• A scientific theory is very different from a normal

theory. There are 3 ways to use a theory:

1. Normal person: just a guess. Sometimes silly.“Sam is late for class. He must have been abducted by aliens!”2. Semi-scientific: sometimes people will use hypothesis and theory interchangeably.“My theory is that Diet Coke & Mentos is the biggest explosion.” (should have said “hypothesis” instead)3. Scientific theory: An almost-indisputable explanation that’s constantly being tested. It’s a fact!“Germ theory states that some diseases are caused by microorganisms like bacteria.”

Scientific TheoriesYou can call scientific theories facts.

• Germ theory• Molecular theory• Evolution• Theory of relativity (E=mc2)• Gravity• Plate tectonics• Climate change

Scientific Laws vs. Theories

Scientific law: Describes patterns that you always see in nature without trying to explain why. Usually involves math. “Narrow”

Scientific theory: Explains why you usually see a particular thing in nature. The observations are indisputable facts and the theory is constantly being tested. “Broad”

The main difference is the “why.” e.g. It’s germ theory because you can’t just throw math at it and figure out what disease bacteria will cause. (This is a very simplified explanation.)

Scientific LawsYou can also call scientific laws facts.

• Law of conservation of energy• Hooke’s law (how a spring coil moves)• Newton’s law of universal gravitation (different

from the theory of gravity because it doesn’t apply to things like black holes)

Most laws look like math equations, but it might be weird math.

Questions• Any questions about the slides?

• Any new questions?

New Questions• What was the most dangerous dinosaur?Possibly the spinosaurus, which hunted on land and sea.

New Questions• What is the most dangerous big cat?

• What is the most dangerous fish apart from sharks?

• What kinds of water snakes are venomous?

• What is the biggest snake in the world?Green anaconda is the heaviest (227 kg); reticulated python is the longest (10 m).