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8th Grade Physical
Science Curriculum
Unit 1: Density
and Buoyancy
Lesson 1, part b.
Generating New Questions, Testing Hypotheses
Objectives:
Students will learn to generate hypotheses, and design simple
experiments to test them. They will also learn that not all liquids
are alike, even if they look alike. Sometimes we have to do experiments
to understand why things behave the way they do.
Key Question: How can we predict if something will sink
or float?
Outline:
This teacher-led activity serves to introduce the students to
the inquiry cycle and allow them to go from hypothesis to experiment
repeatedly, reinforcing the open-ended nature of inquiry. Scientists
do not begin investigations knowing the outcome. We begin with
questions, and we perform experiments as a way of probing for
answers.
Time:
30 to 45 minutes
Materials; For
the Teacher:
Two clear glass 250 or 500 ml beakers, labeled A and B
Two+ ice cubes (you should have extras)
200 ml of alcohol, isopropyl or ethanol
200 ml of water
Salt
Vinegar
Assessment:
Student responses to the homework question will reflect their
understanding of sinking and floating.
Textbook reference: pages 82 -88
Homework Challenge:
We have established by switching the ice cubes that the key to
this puzzle is the behavior of the liquids. The ice cube floats
in water, but sinks in alcohol. The ice cube hasn't changed.
What is it that makes it sink in one liquid but float in another?
OUSD/California Science Content
Standards: 5c and 5d; buoyancy,
floating and sinking (Calif. #8.8c and d)
Procedure:
Step One: We have presented students with a discrepent event;
an outcome that violates their expectations. This poses a problem,
or a question, which calls for hypotheses. Record on the board
the question, and have students brainstorm hypotheses, which
should be recorded on the board and in students' notes.Here are
some likely hypotheses and some very quick experiments you can
do to check them:
Question: Why did the ice sink in
Beaker A but float in B?
| Hypothesis |
Test |
| The
ice cubes are different. |
Switch
the ice cubes. |
| The
water in A is hot. |
Allow
students to touch the beakers. |
| The
water in A is salty. |
Add
salt to B. |
| Liquid
A is vinegar. |
Pour
vinegar in a third beaker, then add an ice cube. |
| Liquid
A is alcohol |
Allow students
to smell the beaker. |
Step Two:
When students succeed in discovering that Liquid A is alcohol,
they will be quite pleased with themselves. But if you look at
the question above, it is not really answered by this discovery.
So what if the liquid is alcohol? Why does an ice cube sink in
alcohol, but not in water? This becomes our new question to investigate.
Point out to students that science does not often arrive at final
answers. Usually, as we gain knowledge, we find new questions
to answer.
Investigation Cycle Note:
Notice that you have completed a short Inquiry sequence with
the students. A question was posed following some observations,
hypotheses were proposed and tested, and new questions are emerging.
Point this out to the students, as this is the process that will
drive our investigations all year long.
Unit
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