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“How does soap clean?”

“Where does plastic come

from?”

“Why do we need sunscreens?”

Have you ever wondered…

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“Why do we get hot when we

work out?”

“Why does fire transform wood to ashes, but ashes can’t become wood again?”

Have you ever wondered…

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The universe obeys a set of unwritten rules…

… called natural laws.

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Science is about discovering…

… what those natural laws are.

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How can we approach these questions?

Questions

Evidence

Theory

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Your 1st investigation

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Your 1st investigation

Two important rules:

• Objectivity

• Repeatability

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Does sugar dissolve faster in hot water?

Can you make an educated guess?

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“I think sugar dissolves faster

in hot water.”

Does sugar dissolve faster in hot water?

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hypothesis: a tentative explanation for something, or a tentative answer to a question.

“I think sugar dissolves faster

in hot water.”a hypothesis!

Does sugar dissolve faster in hot water?

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experiment: a situation specially set up to observe how something happens or to test a hypothesis.

Testing a hypothesis requires scientific evidence from experiments.

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One experimental setup:

Objective observation:The time it takes the sugar to dissolve changes in each trial.

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One experimental setup:

Does this support our hypothesis? YES NO MAYBE

“I think sugar dissolves faster in hot water.”

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One experimental setup:

Does this support our hypothesis? YES NO MAYBE

“I think sugar dissolves faster in hot water.”

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One experimental setup:

What could affect dissolving?

• Water temperature• Amount of sugar• Amount of water

Variables

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variable: a quantity that is measured or changed in an experiment or observation.

What could affect dissolving?

• Water temperature• Amount of sugar• Amount of water

Variables

We don’t know if our hypothesis is correct because more than one variable changed at the same time!

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A second experimental setup:

Objective observation:The time it takes the sugar to dissolve changes in each trial.

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What could affect dissolving?

• Water temperature• Amount of sugar• Amount of water

Control variables (do not change)

A second experimental setup:

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What could affect dissolving?

• Water temperature• Amount of sugar• Amount of water

Experimental variable (changes)

A second experimental setup:

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Does this support our hypothesis? YES NO MAYBE

“I think sugar dissolves faster in hot water.”

A second experimental setup:

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Does this support our hypothesis? YES NO MAYBE

“I think sugar dissolves faster in hot water.”

A second experimental setup:

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variable: a quantity that is measured or changed in an experiment or observation.

experimental variable: the single variable that is changed to test its effect.

control variable: variables that are kept constant.

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These numbers are different!

The same experiment is repeated 3 times.

The measurements are different each time.

Is the investigator making a mistake?

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error: the unavoidable difference between a real measurement and the unknown true value of the quantity being measured.

• Measurements always contain some uncertainty or error.

• In this case, error is not a mistake.

Error and uncertainty

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Accuracy

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Why take the average?

• To improve accuracy

• Comparing the actual measurement

with the average gives you an

estimate of the error

Accuracy

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How can we know the error if we don’t know the true value?Assume the average is the true value.

Accuracy

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Does sugar dissolve slower in warmer water?

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Estimated error: +/– 4 seconds

Estimated error: +/– 4 seconds

Does sugar dissolve slower in warmer water?

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0.6 seconds

Estimated error: +/– 4 seconds

Estimated error: +/– 4 seconds

Does sugar dissolve slower in warmer water?

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0.6 seconds

Estimated error: +/– 4 seconds

Estimated error: +/– 4 seconds

No, the difference in time (0.6 s) is not significant, because it is smaller than the

estimated error (4 s).

Does sugar dissolve slower in warmer water?

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The scientific method

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Variables Experimental

Control

Repeatability

Uncertainty

Precision/accuracy

ObjectivityStating only

what happened