1. Theory: In this lab, we used the equation (Fb = pgV) to figure out the buoyancy of three different objects. We then used a force sensor to give us an actual reading of the force, or weight, of the object and we found the buoyant force by using the equation (Fb = Wout – Win). We then used our theoretical value for buoyancy and our measured value to find the percent error. Lastly, we used a tuna can as a boat and found the volume of the tuna can. This volume is the supposed capacity that the can will hold before sinking in the water.
2. Procedure: The first thing we did was measure the volume of the three objects. For the aluminum cylinder, we measured the radius and length (V=pi R^2 h) to find a volume of 2.29X10-5m^3. We measured the radius of a brass sphere (V=4/3 pi R^3) to find a volume of 2.91X10-5m^3. And lastly, we measured the length, width, and height of an aluminum block (V=LWh) to find a volume of 4.03X10-5m^3. Next, we used the buoyancy equation, plugging in the density of water and the volume of our object, to find the predicted buoyant force. Next, we used a force sensor and weighed our three objects before they were placed in water, and while they were submersed and solved for the actual buoyant force. We compared these two numbers and solved the percent difference. Finally, we measured the radius and height of the tuna can to give us a volume of 211.86cm^3. This means that the tuna can should be able to hold just about 211.86g of weight before it sinks.
3. Results: After completing this experiment, we predicted a buoyant force of 0.224N for the aluminum cylinder but the measured force was 0.23, a 2.68% difference. We predicted a buoyant force of 0.286N for the brass sphere but the measured force was 0.29, a 1.40% difference. Lastly, we predicted a buoyant force of 0.395N for the aluminum block but the measured force was 0.38, a 3.80% difference. For the tuna can, we predicted that it can hold 211.86g of weight before sinking, but after we completed the experiment, we found that it could only hold 190.0g.
4. Conclusion: In this lab, we tried to find buoyant forces for three different objects. For this lab, we had very good tools that helped us find the forces. The only issue that we had was that the force sensor was not 100% calibrated no matter how many times we did it. The error was very small however, and it still allowed for very good results. For the tuna can, we did not have the best equipment for placing the weights inside the can. The weights need to be evenly distributed throughout the can but with just our big hands and the small can, it is difficult to put them all in the center of the can. All in all, however, this lab was excellent and explained buoyancy in much greater detail.