Claims, Evidence, Reasoning
and Rebuttal
Keith Miller
University of Denver
August 22, 2012
[email protected]
Physics
of the
Summer Olympics!
http://www.nbcolympics.com/sports/index.html
Hometown hero!
http://www.nbcolympics.com/sports/index.html
So I was wondering….
What forces do swimmers contend
with to propel themselves through
the water?
Thrust
Drag
Drag
• We really can’t get wet today!
• Air is a fluid (just like water)
• Drag activity
Focus Question:
What affects the force of drag
as an object (swimmer) moves
through a fluid (water)?
Plastic Bag activity**
• Break into groups of 6 OR 8 participants!
• In pairs, acquire a “drag chute”.
• Wait for further instructions!
** This activity was adapted from the Wings Aerospace Science Program (WASP) available
through the Wings Over the Rockies Air and Space Museum
Remember to make observations!!
• Observations are evidence – you will
need these to support your claim(s)
later.
• Use observations of others --- pool
resources to increase your data set!
Overview
1. Run the “track” with a partner with your
drag chute furled.
2. Repeat your “sprint” with your partner
with the chute “unfurled”.
3. Repeat step 2 above with your chute at a
different “angle of attack”.
4. In groups of 6 or 8, repeat step 2 with
pairs following behind each other about 2
feet; alternate groups so that each group
is the lead group at least once.
Prediction and Plan
• Write down as many possible predictions
and/or outcomes from the plan detailed.
• Make a short plan…
– How and where are you going the hold the
bag?
– How big do you want it?
http://www.nbcolympics.com/sports/index.html
What can you claim?
• Make 1 claim related to the focus question on
drag
• Support your claim with evidence from your
activities
• What experiment would you like to do next?
• Can you reduce or increase the drag of your
“drag chute”?
Mathematical expression of Drag
velocity of object traveling in fluid
density of fluid
1 2
Fdrag = rn Cd A
2
drag coefficient
reference area of object traveling
in fluid
Some NASA definitions
• Drag – mechanical force generated by a
solid object moving through a fluid
• Form drag – depends on the shape of
the object
• Skin friction – interaction between air
(or water) molecules and surface of
object
http://www.grc.nasa.gov/WWW/k-12/airplane/drag1.html
Revise you Claims and
Evidence
• Add a reasoning piece to your claims and
evidence
– Jot down words or phrases that might help
– Can you recall any Laws that might help
Relationship to NGSS
• MS.PS-FM (f) Analyze and interpret data to
determine the cause and effect relationship
between the motion of an object and the
forces acting upon it.
Writing prompt
While passing students in the hallway, you overhear
the following exchange:
Donna: Missy won the 100-meter backstroke because
she stayed underwater longer on her start and turn.
You swim much faster underwater.
Dan: No way Donna! Everyone knows that you swim
faster on the surface of the water. She got to the
surface faster and had a stronger kick!
Which student is correct? Are either correct? Using
CER, support or defend the student comments.
Follow-up on theory
• NBC Learn site
The above site has great tutorials on many
subjects including the science of the
Summer Olympics. There are two videos
that involve swimming – one on fluid
dynamics of swimming and the other on the
design of “fast” swimming pools!