```Observation vs. Inference
Review - Observation
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What is an observation?
– Using your five senses to take note of and
Inference
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An inference is when you make an
that you observe
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After you make an observation, you usually
make an inference about what is going on
Let’s practice making inferences!
The next three slides show some fossil imprints that
were found during a archeological dig. We’re
going to record some observations and then make
some inferences about what may have happened
millions of years ago….
What do you think happened?
&frac12; page – be DETAILED please) describing
what you think happened to the creatures in
our fossil evidence
please complete the ‘Inference’ portion of
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P. 4 “Hypothesis, Variables, Constants,
Controls”
Hypothesis
Hypothesis: an educated guess or prediction;
an “if, then” statement
If ____independent variable______
then__dependent variable_______
Example:
Independent Variable:
I feed my cat a lot of food
Dependent Variable
she will get fat
If ___________________________
then _________________________
Remember
Try to use INCREASE and DECREASE in
Ex. IF I increase the amount of food I give my cat,
THEN she will increase her weight
Use the following statements and write a good hypothesis – think
about how one thing will affect the other and use your ‘if, then’
statements. Try using the words “increase” and “decrease”
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1) Chocolate may cause pimples.
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2) Salt in soil may affect plant growth.
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3) Bacterial growth may be affected by temperature.
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4) Sunlight may cause skin cancer.
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5) Temperature may cause leaves to change color.
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Types of Variables
There are 2 main types of variables:
Independent Variable: The variable that is changed
by the scientist; the ‘I control’ variable
Dependent Variable: The variable that might change
because of what the scientist changes – what is
being measured
Your hypothesis can TELL you what your
variables are!
Ex. If I drink Mountain Dew before bed, then
I will not sleep very much.
IV: Drinking Mountain Dew
DV: the amount of sleep
Practice
Use this hypothesis to identify the variables:
If I leave all the lights on all day,
then my electric bill will be expensive
IV: lights on
DV: electric bill will be high
If I brush my cat more, then there will be less
fur on my furniture
IV: brush my cat
DV: fur on furniture
Now read the following experiment and identify
the independent and dependent variables
Elizabeth wanted to test if temperature affected how fast milk
goes bad and curdles. She left milk in a room temperature
closet, a fridge, and a oven that was turned on low heat.
She then measured how rotten the milk was after 10 days.
IV: temperature
DV: rottenness of milk
Variable Practice
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Puzzle Example
Students of different ages were given the same jigsaw puzzle to put together. They were timed to see
how long it took to finish the puzzle.
Independent Variable-different aged students
Dependent Variable-time to finish puzzle
Electromagnetic Example
An investigation was done with an electromagnetic system made from a battery and wire wrapped
around a nail. Different sizes of nails were used. The number of paper clips the electromagnet could
pick up was measured.
Independent Variable-sizes of nails
Dependent Variable-number of paper clips picked up
Egg Example
The higher the temperature of water, the faster an egg will boil.
Independent Variable-temperature of water
Dependent Variable-time for egg to boil
Depth Example
The temperature of water was measured at different depths of a pond.
Independent Variable-depth of pond
Dependent Variable-temperature
Constant
Constant: something that scientist makes sure is the
same throughout the experiment
Ex. Watering the plants the same amount of water or
making sure you are testing the same person every
time
Control
Control: The part of the experiment that the
scientist doesn’t change or add the variable
to
Ex. The plant with the white light
Two 10th grade students wanted to know the effect of shoe
brand on speed. They took 2 brands of track shoes (Nike
and Adidas) and measured 50-yard dash times in each
brand of shoe. They thought that the Nike shoes would be
faster. They compared the dash times to see which shoe
resulted in the lowest sprint times.
1. Independent variable: type of shoe
Dependent variable: time to run 50-yard dash
2. Hypothesis: If I wear Nike track shoes, then I will decrease my time
for the 50-yard dash
Laura loved to chew gum– and she especially liked to blow
bubbles. She wondered if the type of sweetener (real sugar
or artificial sweetener) affected the size of the bubble. She
assumed that they would be the same size. Laura got a
pack of regular gum and a pack of sugar-free gum and
chewed each. She blew the largest possible bubbles for
each type of gum– then she measured the size of the
bubbles to see if the sweetener type made a difference.
1. Independent variable: type of sweetener
Dependent variable: size of bubble
2. Hypothesis: If I chew gum with artificial sweetener,, then it will not
effect the size of the bubble I can blow.
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“I want to see if different colors of light help plants grow
better. I am going to take four plants (all the same type)
and set them up underneath different lights. One will be a
white light, one will be red, one will be blue, and one will
be green. Everyday, I will water them the same amount at
the same time. I will also record how high each plant
grows for two weeks and then look at my results.”
What is the independent variable? Color of light
What is the dependent variable? Height of plant
What are the constants?
1. amount of water
2. time watered
3. type of plant
What is the control? Plant grown in white light
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“I want to see how taping my thumbs will affect my time it
takes to button up a shirt. I will test the same person – they
will do three trials buttoning up the same shirt with their
thumbs taped to their palms. Then I will do three trials
where their thumbs are not taped up. I will average the
time in seconds that it takes to button up and shirt with
their thumbs taped and without their thumbs taped.”
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What is the independent variable? Taping/non-taping of thumbs
What is the dependent variable? time
What are the constants?
1. same person
2. same shirt
What is the control?
Time with thumbs not taped
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“I want to see if there if drinking a lot of milk will affect
how much you eat at dinner. I will take 5 people. For three
days, I will give them two glasses of milk to drink before
they eat dinner. I will serve the same food for those three
days and they will eat at the same time every day. After
three days of drinking milk, I will then have the people eat
for three days without drinking milk before they eat dinner
(again, same food, same time). I will measure how much
food they eat in the three days that they drink milk and the
three days that they don’t drink milk and compare my
results.”
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What is the independent variable? Milk drank or not
What is the dependent variable? Amount of food eaten at dinner
What are the constants?
1. same food
2. same time
3. same people
What is the control?
Amount eaten when milk is not drank
before dinner
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