1. SeaPerch Buoyancy Lesson
IOT POLY ENGINEERING
SP-2
SeaPerch Buoyancy Lesson
Oceanography
Mrs. Brostrom
October 11, 2013

2. Supplies Needed 1’x1’ alum foil Weights Water tubs Graduated cylinders
12 oz (or smaller) cups
160 g sand for each team

3. DRILL SP-2 What is more relevant to keep objects floating:
IOT POLY ENGINEERING
SP-2
DRILL
What is more relevant to keep objects floating:
Weight or Shape
1. Using the tub of water and the piece of aluminum foil, determine what makes an object float:
Come up with 2 different floating boat shapes.
How much mass can each hold?

4. BUOYANCY SP-2 Weight and Buoyancy
IOT POLY ENGINEERING
SP-2
BUOYANCY
What are the forces acting on the iceberg below?
Weight and Buoyancy
Force of Gravity
= Weight
Buoyancy

5. BUOYANCY What is weight? What is buoyancy? SP-2
IOT POLY ENGINEERING
SP-2
BUOYANCY
What is weight?
The downward force of gravity acting on an object
What is buoyancy?
Buoyancy is the upward force that keeps objects afloat
Force of Gravity
= Weight
Buoyancy

6. B = (Vobject) x (rfluid)
IOT POLY ENGINEERING
SP-2
BUOYANCY
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)

7. IOT POLY ENGINEERING
SP-2
BUOYANCY LAB
What is the volume of the plastic cup you were given at the beginning of class?
What is the density of water?
Volume = 12 oz = 355 mL
rwater = 1 g/mL

8. B = (Vobject) x (rfluid)
BUOYANCY LAB
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
Why, then, does the cup float?
The weight of the displaced water is greater than the weight of the cup.

9. IOT POLY ENGINEERING
SP-2
BUOYANCY LAB
How much weight of sand will it take to overcome the buoyancy force and sink the cup?
Test this theory:
There are about 160 grams of sand in the second cup you have.
Add sand until the cup begins to sink.
DO NOT let water infiltrate the sand.
355 grams

10. IOT POLY ENGINEERING
SP-2
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?

11. Submarines A valve opens and tanks in the submarine fill with water.
The added water increases the weight of the submarine and it sinks.
These tanks are called ballast tanks and the water/weight it picks up is called ballast.
Weight < Buoyancy
FLOATS
Weight > Buoyancy SINKS

12. Submarines SP-2 How does the submarine then rise back to the surface?
IOT POLY ENGINEERING
SP-2
Submarines
How does the submarine then rise back to the surface?
It uses compressed air from tanks on board to force the ballast water back out, leaving only air.
The buoyancy force then becomes greater than the weight, and the submarine rises.
Weight > Buoyancy SINKS
Weight < Buoyancy
FLOATS

13. Let’s Review SP-2 What is buoyancy?
IOT POLY ENGINEERING
SP-2
Let’s Review
What is buoyancy?
Which matters most; weight or shape?
How do submarine sink and rise?

14. Balancing our Sea Perch