1. IOT POLY ENGINEERING SP-2 Lesson designed by Mick Scott, Baltimore Polytechnic Institute, mscott@bpi.edumscott@bpi.edu References (for pictures, ideas, etc.) are provided in the “notes” space attached to the relevant slides. SeaPerch Buoyancy Lesson

2. IOT POLY ENGINEERING SP-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

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

4. IOT POLY ENGINEERING SP-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

5. IOT POLY ENGINEERING SP-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 = Volume object x density fluid B = (V object ) x ( r fluid )

6. IOT POLY ENGINEERING SP-2 BUOYANCY LAB 1.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 r water = 1 g/mL

7. 3.If the cup were nearly submerged in water, what is the buoyancy force acting on it? B = (V object ) x ( r fluid ) = (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

8. IOT POLY ENGINEERING SP-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

9. 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?

10. Submarines 3.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 < Buoyancy FLOATS Weight > Buoyancy SINKS

11. IOT POLY ENGINEERING SP-2 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. 8.The buoyancy force then becomes greater than the weight, and the submarine rises. Weight < Buoyancy FLOATS Weight > Buoyancy SINKS

12. IOT POLY ENGINEERING SP-2 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. 3.What is the relationship between the weight and the buoyancy of this experiment? Weight > Buoyancy Motion

13. 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

14. Buoyancy Ballast Submarine sinking and rising Diving Bell Lesson 2: Topics Covered IOT POLY ENGINEERING SP-2