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IOT
POLY ENGINEERINGSP-2
• Lesson designed by Mick Scott, Baltimore Polytechnic Institute, [email protected]
• References (for pictures, ideas, etc.) are provided in the “notes” space attached to the relevant slides.
SeaPerch Buoyancy Lesson
IOT
POLY ENGINEERINGSP-2
April 21, 2009
1. Get your SEAPerch notebook.2. Using the tub of water and the piece of aluminum foil,
determine what makes an object float:1. Come up with 2 different floating boat shapes.2. How many marbles can each hold?
DRILL
What is more relevant to keep objects floating:
Weight or
Shape
Supplies Needed:
1)1’x1’ alum foil
2)Marbles
3)Water tubs
4)Water sinks
5)Graduated cylinders
6)12 oz (or smaller) cups
7)String and ballast (for diving bell)
8)160 g sand for each team
IOT
POLY ENGINEERINGSP-2
BUOYANCY
What are the forces acting on the iceberg below?
Weight and Buoyancy
Force of Gravity = Weight Buoyancy
IOT
POLY ENGINEERINGSP-2
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 Gravity = Weight Buoyancy
IOT
POLY ENGINEERINGSP-2
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
POLY ENGINEERINGSP-2
BUOYANCY LAB1. What is the volume of the plastic cup you
were given at the beginning of class?
2. What is the density of water?
Volume = 12 oz = 355 mL
rwater = 1 g/mL
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
IOT
POLY ENGINEERINGSP-2
BUOYANCY LAB
4. How much weight of sand will it take to overcome the buoyancy force and sink the cup?
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).
355 grams
IOT
POLY ENGINEERINGSP-2
SubmarinesHow 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?
Submarines3. A valve opens and tanks in the submarine fill
with water.
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.
Weight < BuoyancyFLOATS
Weight > Buoyancy SINKS
IOT
POLY ENGINEERINGSP-2
Submarines6. 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.
8. The buoyancy force then becomes greater than the weight, and the submarine rises.
Weight < BuoyancyFLOATS
Weight > Buoyancy SINKS
IOT
POLY ENGINEERINGSP-2
Diving Bell Lab1. 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.
3. What is the relationship between the weight and the buoyancy of this experiment?
Weight > Buoyancy
Motion
4. Take your tubing and insert it into the cup.5. Slowly blow air into the cup and observe what
happens.
6. Now what is the relationship between weight and buoyancy?
7. How does this “diving bell” lab demonstrate ballasting that sinks and raises submarines?
Diving Bell Lab
Motion
Buoyancy > Weight
• Buoyancy• Ballast• Submarine sinking and rising• Diving Bell
Lesson 2: Topics Covered
IOT
POLY ENGINEERINGSP-2
