Transcript Slide 1

Why is SAFETY such an
important issue in science?
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Safety is very important in science to keep
students safe and healthy. It is also
important to keep from damaging
equipment and supplies.
Students saw advertisements for two brands of light
bulbs.
The students are unsure how to decide which brand of
light bulb is the better buy.
Describe two additional pieces of information that
would help the students decide which light bulb is the
better buy.
– Explain how each piece of information will help the
students make a decision.
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To make an informed decision, the students need to
know how much each light bulb costs and how
long each light bulb lasts. If they know these
things, they can compare the savings with the
longer life. Saving $0.50 on a light bulb that costs
$2.00 is probably better than getting an extra 30
hours from a light bulb that lasts 3000 hours. But,
if the light bulbs are more expensive or last a
shorter time, then the longer light bulb life might be
a better deal than saving $0.50. They cannot tell,
though, without knowing the price and life of each
bulb.
What are the three
kinds of variables?
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The three kinds of variables are
independent variables, dependent
variables, and controlled variables.
Explain the term HYPOTHESIS
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A hypothesis is a special kind of prediction.
It is an education guess about the
relationship between variables. It can be
tested with a scientific investigation. A
hypothesis can be written as an If, Then
statement.
Why do scientists use tools,
such as thermometers and
meter sticks, when they
make observations?
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Tools help scientists make observations
that are accurate and precise.
Why is it important for scientists to
communicate their data?
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• It is important for scientists to communicate
date so that other people can learn from them.
• Also, communicating results lets other
scientists repeat the experiment and verify it.
Why do scientists use
models?
Give an example of a
model
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• Models let scientists observe things that are
too big, too small, too expensive, or too
dangerous to observe otherwise.
• A globe is a model
List at least three things you
should be careful to do when
designing an experiment.
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limit the number of variables being tested
conduct enough trials to get sufficient data
eliminate bias
prepare good data tables
consider safety
measure carefully
Students filled four identical glass beakers with the amount of water
shown in the table below. Using a hot plate, the students heated the
water in the two beakers to 60 °C and allowed the water to cool for a
period of time. The water in the two other beakers was heated to 80 °C
and allowed to cool for the same period of time. The table shows the
final water temperature in each beaker.
– What are two conclusions that the students should draw about factors
affecting the cooling rate of water?
– Use data to support these conclusions.
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One conclusion is that the hotter water is, the
faster it cools. For the 200 mL samples, the
hotter sample lost 22 °C, and the cooler one
lost 14 °C. For the 400 mL samples, the hotter
one lost 13 °C, and the cooler one lost 8 °C.
Another conclusion is that larger volumes of
water cool more slowly. For the samples at 80
°C, the larger one lost 13 °C, and the smaller
one lost 22 °C in the same amount of time.
The cooler water samples followed the same
pattern.
A group of students determined the percentage of electricity
derived from various energy resources for two different regions.
Their data is shown in the table above.
– Which type of graph is MOST suitable for displaying this
data?
– Explain why.
– Represent the data in two separate graphs.
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A student wants to know if the mass of a
magnet determines how strong it is.
– Identify the tools needed to collect the data.
– Describe in detail how the student could
collect information to answer this question.
– Explain how to analyze the data to draw a
conclusion.
– Draw and label the columns of a chart or
table that could be used to organize the data
collected in the experiment you describe.
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The tools needed for this experiment are magnets of
different sizes, small objects that could be attracted to
the magnets, and a measuring device such as a
balance or spring scale. To collect data for this science
experiment, students will need to know both the size
and strength of different magnets. They could measure
how many quarters can be suspended from each
magnet. The data would be placed in a chart for
comparison. The chart may look like this:
Magnet Mass (grams) Number of paper clips held on one end
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Look at the two plants in the experiment. Both plants
are the same type of plant and received the same
amount of water each day.
–What hypothesis do you think the scientist was trying
to study in this experiment?
–Explain how the experiment helps to answer the
scientist's question.
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The scientist was trying to test the hypothesis:
A plant needs light to grow.
The experiment helps the scientist test the
hypothesis because there are two plants that
started out the same. The scientist placed
one plant in the sun and the other in the
shade to test the hypothesis while keeping
the other variables constant in the
experiment. This design limits the variation
between the plants to the amount of light
received by each plant.
Stephanie notices that after she swims her breathing is
faster than it was when she was sitting by the pool. She
thinks that the number of laps that she swims affects
how fast she breathes.
– Develop a hypothesis that Stephanie could use to test
her idea.
– Describe an experiment she could use to test her
hypothesis.
– Identify ONE independent variable and ONE dependent
variable in her experiment.
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Hypothesis: The rate of breathing increases based on the number
of laps Stephanie swims.
If the number of laps increases, then the breathing rate will
increase.
Experiment: Stephanie can find out how many breaths she
takes per minute while resting. She can then swim 5 laps and
count the number of breaths she takes per minute. Stephanie
can then rest until her breathing is back to a normal resting
amount and swim 10 laps and count the number of breaths she
takes per minute. She can continue these steps for up to 30
laps. During each test, Stephanie should swim at the same
speed.
Independent variable: number of laps Stephanie swims
Dependent variable: breathing rate per set of laps
In 1648, a Flemish alchemist, Jan van
Helmont, had a theory. To test it, he grew
a tree in a tub of soil, adding nothing but
measured quantities of water for five
years. During that time he kept track of
the weigh of the soil and the tree. At the
end of the experiment the tree had gained
164 pounds and the soil had lost 2
ounces. What could von Helmont
conclude from his experiment?
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Most of the tree’s increase came from something
other than the soil
A student needs to heat a beaker of water on
a hot plate.
– Identify a safety precaution the student
should take before plugging in the hot plate.
– Explain why the safety precaution is
necessary.
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The electrical cord of the hot plate should be
checked before plugging in the hot plate
because a frayed cord could lead to an electric
shock.
A team of three students obtains a set of test tubes from the
teacher. Each test tube contains a different colored powder. The
students dissolve the powders in water without labeling the test
tubes. The students then realize that they have forgotten which
test tube is which. Each student suggests a solution to the
problem.
Describe a safety hazard for each of the student's solutions
described in the table.
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All of the solutions from the students are potentially
dangerous. Amanda wants to taste each solution. Because
the powders were unknown, she can't tell whether the
liquids are poisonous. Tasting the liquids could make the
students sick. Kai wants to try mixing chemicals with the
liquids to test their reactions. Because she doesn't know
what the chemicals are, Kai can't be sure what the
reactions will be. The reactions could be explosive or
release toxic fumes. Damon wants to get a Bunsen burner
and boil each liquid. Because he doesn't know what the
liquids are, Damon can't predict how they will react to
being heated. He can't tell whether the liquids are
flammable. To solve their problem, the students should let
the teacher know what happened and see if there is a safe
way to figure out which liquid is which. If not, they may
need to repeat the experiment.
A student needs to buy sunscreen for a trip to a local water
park. The store had the two brands shown below. The student
wanted to decide which sunscreen would be the best to use.
– Name two misleading statements on one of the labels.
– Explain why the statements you selected are misleading.
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Brand one is misleading because it says that it is
water resistant, but if you have to reapply it
after swimming and sweating, it is not
waterproof under the conditions most users
would use it for. It is also misleading because
it says it is pediatrician tested, but it does not
say what the results of the test were. It might
have been tested and found to be inferior to all
of the other brands that were tested.
To find the mass of some iron filings, a student places the filings in a 14gram plastic tray and places the tray on a balance.
–What is the reading on the balance for the mass of the tray and iron
filings?
–What is the mass of the iron filings?
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The balance reading is 352 grams. Because the
tray has a mass of 14 grams, the mass of the
iron filings is 338 grams.
A student added some water to a graduated cylinder. This initial volume is
shown in the graduated cylinder on the left. Then, the student placed a
small rock in the cylinder, as shown in the graduated cylinder on the right.
–What was the volume of water that the student initially added to the
cylinder?
–What is the volume of the rock?
–Describe two characteristics of the rock that can be observed without
touching the rock or using any tools.
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The volume of the water is 35 mL. The volume of
the rock is 17 mL.
One characteristic of the rock that can be
observed is its small size. It must be small to fit
into a graduated cylinder. Also, the rock has
different minerals in it. You can see them in the
light and dark patches on the rock's surface.
Students grow two groups of plants. Ten plants are given fertilizer, and 10
plants are grown without fertilizer. They measure the height of each plant every
other day and find the average height for each group. The table below shows
their data.
The students want to make a graph of this data to learn about the effect of
fertilizer on plant growth.
– Explain which type of graph the students should make.
– Graph the data set onto a single graph. Be sure to title and label your graph.
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A double line graph is best for this data because
the students are working with two groups of
plants and want to show how each group
changes over time.
Determine the
density of the rock
shown in the figure.
Explain how you
determined your
answer and use
appropriate units of
measurement.
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The density of the rock is 4 g/mL. I determined the
density by dividing the mass of the rock by the
volume of water that it displaced in the
graduated cylinder. A ruler could not be used to
find the volume because the rock has an odd
shape.
A student is planning an experiment to learn about the specific heat capacity of
iron, copper, and aluminum. The student plans to follow the steps below.
1. Heat each metal in an oven.
2. Add each metal to an insulated container of water.
3. Use a thermometer to observe water temperature changing.
4. Record the highest water temperature.
5. Compare the highest water temperature for each metal. The metal that leads to
the highest temperature will have the highest specific heat capacity.
For this experiment to work, the student must control several variables.
–Choose two variables that must be controlled in this experiment, and explain the
importance of controlling each variable.
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One variable that must be controlled is the mass
of each metal used in the experiment. The
student must use equal masses of iron,
copper, and aluminum. This is because a
larger mass can hold more heat. This means it
would have more heat to transfer to water.
Another variable to control is the temperature
to which each metal is heated. If a metal were
heated to a higher temperature, it would have
more heat to transfer to the water.
A student used a ruler
to find the dimensions
of a box.
The student recorded
the box's length as 42
mm.
– Explain why the
student's
measurement is
incorrect and give
the correct length.
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The student used 42 mm as the measurement
and didn't take into account that the block
didn't start on the 0 mm mark. The actual block
length is 29 mm.
A student thinks that increasing the concentration
of salt in a saltwater solution will increase the
boiling point of the solution. The student makes
five saltwater solutions, each with a different
concentration of salt. The student uses the same
hot plate to heat each solution. The student uses
the same thermometer to record the temperature
of each solution when it begins to boil.
– Identify the dependent and independent
variables in this experiment.
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In this experiment, the concentration of salt in
each solution is the independent variable. This
is the variable that the student changes
deliberately in each sample. The boiling point
of each solution is the dependent variable. This
is the variable that the student hopes to
change by varying the independent variable.
A group of students is planning a garden of
tomato plants. They want to grow plants that
have as many tomatoes as possible. There
are three different fertilizers they can use in
their garden.
– Design a simple experiment the students
could do to identify the fertilizer they should
use. Include all the elements for a fair,
scientific test in your answer.
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The experiment should have 20 tomato plants—
five tomato plants for each type of fertilizer, and 5
control plants to be grown without fertilizer. Over
several months, each plant would be given the
same amount of water, sunlight, and fertilizer
(except the controls, which only get water and
sunlight). To analyze their results, students
should count the total number of tomatoes
produced by each group of plants. Students
should use the fertilizer used by the group of
plants producing the most tomatoes. If the
control group produces the most tomatoes,
students should not use fertilizer in their garden.
Students want to test a local company's claim
that its paper towels are more absorbent than
the leading national brands.
– Design a simple experiment the students could
use to test this claim. Include all the elements for
a fair, scientific test in your answer.
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Each brand should be evaluated on its absorbency.
Students should obtain 5 sheets of several brands of
paper towel. Students should make sure each sheet is
the same size. Each sheet can be dipped into a
beaker containing 1 liter of water for 30 seconds. Then
students should remove the sheet and record the
volume of water remaining in the beaker. Students
should subtract this volume from 1 liter to find the
amount of water absorbed by the sheet. To determine
which towel is more absorbent, the 5 test values for
each brand should be averaged. If the local brand has
the highest average value, its paper towels are the
most absorbent.
Ben Franklin carried out detailed measurements of water
temperature while crossing the Atlantic Ocean. He used this
data to plot the location of the ocean current known as the
Gulf Stream. This current carries warm water north along
the East Coast of North America and east across the North
Atlantic toward Europe. The Gulf Stream is part of a circular
pattern of water in the Atlantic Ocean. The current can flow
as fast as 7 km/h, which is very fast for an ocean current.
– Describe how this knowledge has affected people's lives
in modern society.
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Today, knowing about the Gulf Stream helps us
to understand weather and climate. We know
that the flow helps carry warm water from the
equator along the Eastern United States and
toward Northern Europe. Scientists know that
hurricanes formed in tropical waters are likely
to follow the Gulf Stream. This can help them
predict which areas will be damaged by
storms.
What is a judgment based
on what has been
observed in an
experiment?
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A judgment based on what has
been observed in an experiment
is a conclusion.