the ability to float.. or this balloon? this bowling ball roughly the same size your students...
TRANSCRIPT
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Buoyancy
What is buoyancy?
The ability to float.
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BuoyancyWhich one is more likely to float?
https://www.youtube.com/watch?v=zm-AkvwPdZ4
Or this balloon?This bowling ball
Roughly the same size
Your students probably already understand some of the basics…
hh
w w
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Buoyancy
Density = mass/volume
Even though they are the same size (dimensions),the balloon will float because it is less dense than the fluid around it!
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Buoyancy
THIS GUY
Was Archimedes buoyant?!
“Any body wholly or partially
immersed in a fluid
experiences an upthrust equal
to, but opposite in sense to,
the weight of the fluid
displaced.”
“Any body wholly or partially
immersed in a fluid
experiences an upthrust
equal to, but opposite in
sense to, the weight of the
fluid displaced.”
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BuoyancyArchimedes looked at forces
Buoyancy: upward force on an object
Gravity: downward force on an object
Pressure: force all around an objectThe ability
to float.
Gravity
Buoyancy
Pressure Pressure
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Buoyancy
Archimedes principle simplified
A body immersed in a fluid experiences a buoyant force equal
to the weight of the fluid it displaces
Upward force (buoyant force)equal to the weightof the displaced fluid
Downward force equal to the weightof the object
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BuoyancyTypes of Buoyancy
Positively Buoyant Neutrally Buoyant
Negatively Buoyant
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BuoyancyRemember
these?
Density = mass/volume
When the density of the object equals the density of the water
around it, the object is neutrally buoyant
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Buoyancy
Play with these concepts
Archimedes loves
neutrally buoyant
ROVs
http://phet.colorado.edu/sims/density-and-buoyancy/density_en.html
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So how do we make our ROVsneutrally buoyant?
Buoyancy and Balance
Once you drill holes in your frame, your
ROV will be negatively buoyant
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Buoyancy
BallastDynamic (soft): system that changes the amount of water displace inside the ballast chamber. (Think submarines)
Static: ballast chamber does not change. ROV is designed to be neutrally buoyant and motors move it up and down. The volume of air stays the same.
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Buoyancy
What types of materials could you use to make your ROV neutrally buoyant?
AND LOTS MORE! What are some pros and cons to different
materials?
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Think about how you place buoyant materials
Buoyancy and Balance
Build an ROV Interactive:
http://www.mysticaquarium.org/fun-and-learning/games/302-build-an-rov
What about balance?
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Buoyancy – going further
*NOTE* Totally optional
If your students are grasping the concepts of buoyancy – you can push them further by
introducing some basic calculations.
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Buoyancy – going furtherPVC Pipe
specifications1’’ PVC 1 ¼’’ PVC 1 1/3’’ PVC 2’’ PVC
Diameter (cm) 3.340 4.216 4.826 6.033
Weight in Air (g/cm)
2.532 6.357 7.174 10.000
Volume percm (cc)
8.762 13.960 18.292 28.581
Net Buoyancy (g/cm) [weight in air per cm –
Volume per cm]
-6.230 -7.603 -11.118 -18.581
Calculations provided by the MATE center
Essentially, this figure gives us the “float” value of each cm of PVC
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Then, weigh your ROV!
Fnet (apparent weight or wet weight) of ROV = ____________g
Buoyancy – going further
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If your ROV weighs 645 g, then you will need -645g of positive, buoyant force!
Buoyancy – going further
How many cm of 2’’ PVC pipe would you
need?
~34.712 cm
*You’d probably also want to add in the weight of the 2’’ PVC endcaps to the weight of your ROV before you did the calculation.
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Buoyancy
Buoyancy and BalanceLet’s make these items
positively, neutrally, and negatively buoyant and
balanced!