EXPERIMENT NO. 3: BUOYANCY Did you ever wonder how aircraft carriers and cruise ships are able to carry so much weight and float over the ocean? The objective of the experiment is to design and build a boat with the greatest buoyant force. What you need: triple beam balance, water trough, aluminum foil (at least 1 piece 25 cm X 25 cm per member), 1 foot tape per member, at least 30 (preferably one-peso) coins per person, 4 toothpicks, 2 straws, 2 paperclips, 2 cotton buds, 2 pcs of pasta. What to do: 1. Each member will design his/ her own boat. Use the entire 25 cm X 25 cm of aluminum foil without cutting-out or tearing off any portion. 2. Document the boat-making process for each member. Measure and record the basic dimensions of your boat and take its total mass using the triple beam balance. Weigh also the other materials. Neglect the weight of the tape used. 3. Each of the boats will be tested by floating the boat in water and adding mass. Put in one coin at a time and make sure they are spread over the boat properly to keep it from tipping over. 4. Count and record the number of coins that your boat can carry. The last coin added to the boat (the one that makes it sink) must be removed from the total mass that the boat held. Weigh a one-peso coin to estimate the total weight supported by the boat. 5. Compare your results with your group mates and find out whose boat was able to carry the most coins. 6. Compute the volume displaced by your boat using the equation: (𝑚𝑎𝑠𝑠 𝑜𝑓 𝑏𝑜𝑎𝑡 + 𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑖𝑛𝑠) × 𝑔 = 𝐵𝐹 𝐵𝐹 = 𝛾 𝑉 7. Except for the aluminum foil and tape, choose one item to reinforce your boat from the list above. If you pick to add straws to reinforce your boat, none of your group mates can use straws anymore. The number is fixed so neither can you add or reduce the number of the item you picked/ were assigned nor cut them or bend or reshape them in any manner. Simply secure them on the boats with the tape. Discuss your options with your group mates so that each boat has a unique design and that there are no duplications whatsoever. Resolve the volume displaced by the boat. Record your observations. Show how buoyancy equations are derived for floating and submerged bodies. Discuss its significance in the civil engineering profession if there are any. This should be included in the Discussion of theory. Answer the following: 1. A barge filled with sand approaches a bridge over the river and cannot quite pass under it. Should sand be added to or removed from the barge to get it under the bridge? Explain. 2. An iceberg in the ocean floats with one-eight of its volume above the surface. What is its specific gravity relative to ocean water, which is 64 lb/ft3? What portion of its volume would be above the surface if the ice were floating in pure water? 3. A 1.2-ft3 block of aluminum is tied to a piece of cork (SG=0.22), as shown. What volume of cork is required to keep the aluminum (SG=2.7) from sinking in castor oil (SG=0.96)? 4. A copper (SG=8.8) cylinder of diameter 4 cm and length 15 cm weighs only 14 N when submerged in liquid. Determine the liquid density. Prepare the Data and Results in the format shown below. It should contain data and results for all the boats designed and built in your group. Data and Results: Boat 1 (Name of Member) Insert photo of boat here. Label its dimensions completely. Mass of boat, g Number of coins carried by boat before sinking Mass carried by the boat, g Volume displaced by boat, cm3 Insert photo of boat here. Label its dimensions completely and indicate the reinforcement used Mass of boat + reinforcement, g Number of coins carried by boat before sinking Mass carried by the boat, g Volume displaced by boat, cm3 The complete data and results table shall be shall be reflected on both the individual and group reports. All computational problems shall be included in the problem set at the end of the individual report. Please refer to Assignment Guide for the format and rubrics for assessment.
