Scientific Method

Who uses it?What is it?

Why should I care?

B. Scientific Method

• Hypothesis - testable prediction

• Theory - explanation of “why” – based on many observations &

experimental results

• Scientific Law - prediction of “what”– describes a pattern in nature

Scientific Method in Action

1. Determine the problem.• Example: You got in your car to drive

up here and turned the key but the car wouldn’t start (observation)

2. Make a hypothesis.• Hypothesis: There is something wrong

with the car - battery dead, ignition problem, out of gas

Scientific Method in Action

3. Test your hypothesis.• Test predictions: turn on headlights,

check spark plug wires, dip stick in gas tank

4. Analyze the results.• headlights work, strong ignition spark,

no gas on dip stick-gas gauge reads half full

Scientific Method in Action

• Test predictions: turn on headlights, check spark plug wires, dip stick in gas tank

• Analyze results: headlights work, strong ignition spark, no gas on dip stick-gas gauge reads half full

Scientific Method in Action

5. Draw conclusion. • Gauge inaccurate, out of gas

Inference -

A conclusion reached on the basis of evidence and reasoning.

The school secretary’s voice comes over the intercom asking Suzie to come to the office immediately. From past experience, you know that Suzie is a straight A student that all the teacher’s love. She never breaks the rules, she’s always on time, and she is respectful. So why is Suzie going to the office? Probably to receive a good student award.

Consider another situation. The school secretary’s voice comes over the intercom asking Billy the Blade to come to the office. He’s considered a trouble maker. He’s not often in class, but when he is you know there will be trouble. As the secretary’s voice fades, you hear several students in the class mumble, “Oh-oh, Billy’s done something, and he’s been caught.”

Identify the following as fact (1) or inference (2).

• The school secretary asked Suzie to come to the office.

• Suzie will receive a good student award.• The school secretary asked Billy to

come to the office.• Billy has done something wrong and has

been caught.

Try making a hypothesis for the following situations:

1. You are watching TV and the screen goes black. You try turning on the lights, but nothing happens.

2. Just before dinner you see taco meat cooking on the stove.

3. Greg is an employee of yours. He asked for time off on the opening day of deer hunting, but you could not let him off work. On opening day of deer hunting, Greg’s wife calls and says that Greg is too sick to come to work.

Try making a hypothesis for the following situations:

4. Just before Christmas, your parents spend a lot of time in the basement workshop. You are not allowed to come into the workshop before warning them.

5. Your department leader at work has taken a job with another company. You have a good chance to be promoted to her job. The company’s boss calls you into his office saying he has some good news for you.

Stating the Problem

• What invisible trail does a rattlesnake follow in tracking down its bitten prey?

Gathering Information

• A rattlesnakes eyes are only sensitive to visible light

• A pair of organs located under the eyes detect invisible light in the form of heat

• A rattler’s tongue “smells” certain odors in the air

• The sight or smell of an unbitten animal does not trigger the rattler’s tracking action

Hypothesis• After the snake wounds its victim, the snake follows the

smell of its own venom to locate the animal

Experiment

• Drag a dead mouse that has been struck and poisoned by a rattlesnake along a curved path on the bottom of an empty cage

• Place the snake in the cage• The snake follows the exact trail that has been laid out• Control• Drag an unbitten dead mouse along the path• The snake seems disinterested

Recording and Analyzing Data

• Do the experiment many times

• Record the data

Conclusion

• The scent of venom was the only factor that could cause a rattlesnake to follow its bitten victim.

Murder Mystery

• Terrance Bogg, a well-known billionaire, is found dead on the floor of his office at 7:00 p.m. Saturday evening. He has been shot through the chest.

Agent Klocke of the FBI is called in to solve the mystery. He discovers the following facts:

• Bogg was shot with a 9 mm handgun. The handgun is not in the office now.

• The butler heard the shot at 4:50 p.m. He thought it was a car back-firing.

• The crime scene investigators who looked at the body around 7:45 p.m. said that Bogg had been dead for three to four hours at the time.

• Two people had recently threatened Bogg. A.J. Stokes hated him because Bogg was ruining his business.

• Gladys Jones, who used to be Bogg’s secretary, was fired last Friday. She was seen down at a local tavern yelling that “Bogg should be shot!”

• A.J. Stokes says he was at a family reunion from 2:00 p.m. until 5:00 p.m. Saturday afternoon.

• Gladys Jones was in a car accident at 3:00 p.m. Saturday afternoon. She has been in the hospital ever since with a broken leg and arm.

• A.J.’s wife says that he left the family reunion around 4:30 p.m. to meet with his financial planner.

• A.J.’s financial planner said that A.J. has not had an appointment with him in week, let alone last Saturday.

From these facts, agent Klocke guesses that A.J. killed Bogg

• He gets a search warrant and searches A.J.’s house. He finds a 9 mm handgun hidden in A.J.’s garage.

. In a police lab test, the gun fires a bullet marked exactly like the one found in Bogg’s chest.

• A.J. is arrested for the murder.

• Another case is solved by the famous agent Klocke.

The Scientific Method Solving the Mystery

The Scientific Method Solving the Mystery

Determine the problem

The Scientific Method Solving the Mystery

Determine the problem Who murdered Bogg?

The Scientific Method Solving the Mystery

Determine the problem Who murdered Bogg?

Make a hypothesis

The Scientific Method Solving the Mystery

Determine the problem Who murdered Bogg?

Make a hypothesis After collecting the facts, agent Klocke guesses that A.J. killed Bogg.

The Scientific Method Solving the Mystery

Determine the problem Who murdered Bogg?

Make a hypothesis After collecting the facts, agent Klocke guesses that A.J. killed Bogg.

Test the hypothesis

The Scientific Method Solving the Mystery

Determine the problem Who murdered Bogg?

Make a hypothesis After collecting the facts, agent Klocke guesses that A.J. killed Bogg.

Test the hypothesis Agent Klocke searches Bogg’s house and examines a bullet shot from A.J.’s gun.

The Scientific Method Solving the Mystery

Determine the problem Who murdered Bogg?

Make a hypothesis After collecting the facts, agent Klocke guesses that A.J. killed Bogg.

Test the hypothesis Agent Klocke searches Bogg’s house and examines a bullet shot from A.J.’s gun.

Analyze the results

The Scientific Method Solving the Mystery

Determine the problem Who murdered Bogg?

Make a hypothesis After collecting the facts, agent Klocke guesses that A.J. killed Bogg.

Test the hypothesis Agent Klocke searches Bogg’s house and examines a bullet shot from A.J.’s gun.

Analyze the results The markings match those from the bullet from the victim’s chest.

The Scientific Method Solving the Mystery

Determine the problem Who murdered Bogg?

Make a hypothesis After collecting the facts, agent Klocke guesses that A.J. killed Bogg.

Test the hypothesis Agent Klocke searches Bogg’s house and examines a bullet shot from A.J.’s gun.

Analyze the results The markings match those from the bullet from the victim’s chest.

Draw conclusions

The Scientific Method Solving the Mystery

Determine the problem Who murdered Bogg?

Make a hypothesis After collecting the facts, agent Klocke guesses that A.J. killed Bogg.

Test the hypothesis Agent Klocke searches Bogg’s house and examines a bullet shot from A.J.’s gun.

Analyze the results The markings match those from the bullet from the victim’s chest.

Draw conclusions A.J. is arrested for murder.

C. Experimental Design

• Experiment - organized procedure for testing a hypothesis

• Key Components:– Control - standard for comparison– Single variable - keep other factors

constant, something that is changed on purpose to see the effects

– Repeated trials - for reliability

C. Experimental Design

• Types of Variables– Independent Variable

• adjusted by the experimenter• what you vary

– Dependent Variable• changes in response to the indep. variable• what you measure

C. Experimental Design

Example:

• Hypothesis: Storing popcorn in the freezer makes it pop

better.

• Control: Popcorn stored at room temperature

C. Experimental Design

• Single variable: Storage temperature

• Constants: Popcorn brand Freshness Storage time Popper

C. Experimental Design• Independent Variable:

Storage temperature

• Dependent Variable: Number of unpopped kernels

What is wrong experiment 1:A teacher wanted to

find out whether teaching for a short time worked better than teaching for longer periods of time. She cut all of her classes from 90 minutes to 45 minutes. Most of her students passed at the end of the term, so she decided that shorter classes were better.

A. Not enough subjects.

B. Subjects are not similar.

C. Conditions are not kept the same OR more than one variable.

D. The experiment is not reproducible.

E. No control group.

What is wrong experiment 2:A bakery manager wanted to

find out if using egg whites to make pastry would make his pie crust more tender. He made 5 pies without egg whites. As they baked, he noticed that the pies made with egg whites browned faster, so he took them out 10 minutes early. The other 5 pies without egg whites baked for the total baking time. When he served the pies, everyone said that the first 5 with egg whites were more tender. The bakery manager decided that using egg whites will make his pie crust better.

A. Not enough subjects.

B. Subjects are not similar.

C. Conditions are not kept the same OR more than one variable.

D. The experiment is not reproducible.

E. No control group.

What is wrong experiment 3:A farmer wanted to

know if ABC fertilizer would be good for his beets. He fertilized all his beets with ABC, but didn’t put any fertilizer on his green beans. His beets didn’t do well at all, but he got a great crop of green beans. He concluded that ABC fertilizer was a waste of money.

A. Not enough subjects.

B. Subjects are not similar.

C. Conditions are not kept the same OR more than one variable.

D. The experiment is not reproducible.

E. No control group.