SeaPerch Buoyancy Lesson
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Lesson designed by Mick Scott, Baltimore Polytechnic
Institute, mscott@bpi.edu
References (for pictures, ideas, etc.) are provided in the
“notes” space attached to the relevant slides.
IOT
SP-2
POLY ENGINEERING
Supplies Needed:
April 21,
2009
1)1’x1’
alum
foil
2)Marbles
DRILL
3)Water
tubs
What is more relevant to keep objects floating:
1. Get your SEAPerch notebook.
2. Using theWeight
tub4)Water
of water andsinks
the piece of aluminum foil,
determine what makesoran object float:
5)Graduated cylinders
1. Come up with 2 different floating boat shapes.
Shape
2. How many marbles can each hold?
6)12 oz (or smaller) cups
IOT
SP-2
7)String and ballast (for diving bell)
POLY ENGINEERING
BUOYANCY
What are the forces acting on the iceberg below?
Weight
Force of
= Weight
Gravity
and
Buoyancy
IOT
Buoyancy
SP-2
POLY ENGINEERING
BUOYANCY
1. What is weight?
The downward force of gravity acting on
an object
2. What is buoyancy?
Buoyancy is the upward force that keeps
objects afloat
Force of
= Weight
Gravity
Buoyancy
IOT
SP-2
POLY ENGINEERING
BUOYANCY
3. What causes buoyancy?
Archimedes’ Principle:
An object is buoyed up by a force
equal to the weight of the fluid
displaced by the object.
Buoyancy = Volumeobject x densityfluid
B = (Vobject) x (rfluid)
IOT
SP-2
POLY ENGINEERING
BUOYANCY LAB
1. What is the volume of the plastic cup you
were given at the beginning of class?
Volume = 12 oz = 355 mL
2. What is the density of water?
rwater = 1 g/mL
IOT
SP-2
POLY ENGINEERING
BUOYANCY LAB
3. If the cup were nearly submerged in water,
what is the buoyancy force acting on it?
B = (Vobject) x (rfluid)
= (355mL) x (1 g/mL)
B = 355 grams
4. Why, then, does the cup float?
The weight of the displaced water is greater than the weight
of the cup.
BUOYANCY LAB
4. How much weight of sand will it take to
overcome the buoyancy force and sink the
cup? 355 grams
5. Test this theory:
1. There are about 160 grams of sand in the
second cup you have.
2. Add sand until the cup begins to sink.
3. DO NOT let water infiltrate the sand (it is
needed for other classes).
IOT
SP-2
POLY ENGINEERING
Submarines
How do submarines use the principle of
buoyancy to submerge and re-surface?
• This yellow submarine displaces so much
water that its own weight is not great
enough to have it sink in the ocean.
• How does it sink?
SP-2
IOT
POLY ENGINEERING
Submarines
3. A valve opens and tanks in the submarine fill
with water.
Weight < Buoyancy
FLOATS
Weight > Buoyancy
SINKS
4. The added water increases the weight of the
submarine and it sinks.
5. These tanks are called ballast tanks and the
water/weight it picks up is called ballast.
Submarines
6. How does the submarine then rise back to the
surface?
7. It uses compressed air from tanks on board to
force the ballast water back out, leaving only air.
Weight > Buoyancy
SINKS
Weight < Buoyancy
FLOATS
8. The buoyancy force then becomes greater than
the weight, and the submarine rises.
SP-2
IOT
POLY ENGINEERING
Diving Bell Lab
1. Tie weight to your cup using the given string and
the holes in the cup.
2. Fill your cup ~1/2-full with water, turn it upside
down, and let it sink.
Motion
3. What is the relationship between the weight
and the buoyancy of this experiment?
SP-2
Weight > Buoyancy
IOT
POLY ENGINEERING
Diving Bell Lab
4. Take your tubing and insert it into the cup.
5. Slowly blow air into the cup and observe what
happens.
Motion
6. Now what is the relationship between weight
and buoyancy? Buoyancy > Weight
7. How does this “diving bell” lab demonstrate
ballasting that sinks and raises submarines?
Lesson 2: Topics Covered
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Buoyancy
Ballast
Submarine sinking and rising
Diving Bell
IOT
SP-2
POLY ENGINEERING