Part III: For this experiment we used a digital scale, a metal cup w/spout, a sm
ID: 1841717 • Letter: P
Question
Part III:
For this experiment we used a digital scale, a metal cup w/spout, a small beaker, a large beaker, and a wooden and metal block to test the difference in buoyant force of the objects.
We first recorded the masses of the wooden and metal block to calculate their volumes, weights and densities.
Block
Mass (kg)
Weight (N)
Volume (m3)
Density (kg/m3)
Wood:
0.009
0.0882
1.88 e -3
1.692 e -9
Metal:
0.132
1.2936
1.70 e -5
2.24 e -6
Then we recorded the reading of the water and blocks combined as they were placed in the beakers
Block
Mass: Cup and water
Mass: cup, water & block
Change in mass
Wood:
0.311
0.319
0.007
Metal:
0.31
0.441
0.131
For the next experiment we measured the amount of water displaced on the beakers by overflowing the bigger and measuring the mass of the smaller beaker to measure the amount displaced.
Block
Mass: Cup and water
Mass: cup, water & block
Change in mass
Mass: catch cup empty
Mass: catch cup w/ water
Change in mass of the catch cup
Wood:
0.475
0.477
0.002
0.029
0.057
0.006
Metal:
0.477
0.592
0.115
0.029
0.048
0.019
Block
Mass (kg)
Weight (N)
Volume (m3)
Density (kg/m3)
Wood:
0.009
0.0882
1.88 e -3
1.692 e -9
Metal:
0.132
1.2936
1.70 e -5
2.24 e -6
Experiment B: 1) Compare the change in mass of the spout cup to the change in mass of the catch cup and the mass of the block. How do these three masses compare? Can you create a mathematical formula that connects the three masses? Do this for both the wooden and metal block. 2) What is different about the numbers for wooden block compared to the metal block? Why? Explain your reasoning. 3) For the wooden block, find the percent difference for the mass of the block and the change in mass of the catch cup. [(difference/average)*100%] 4) What buoyant force is acting on the wooden block? On the metal block? (Calculate the buoyant force by taking the change of mass of the catch cup and multiply that by gravity to get the weight of the displaced water. The buoyant force is equal to the weight of the displaced fluid. Compare the buoyant forces to the weights of the blocks. Which one floated and which one sank? Why? What condition must be met for an object to float?Explanation / Answer
1)
For wood:
Change in mass of spout cup = 0.002
Change in mass of catch cup = 0.006
Mass of block = 0.009
Ratio of Change in mass of spout cup to mass of block = 0.002 / 0.009 = 0.22
Ratio of Change in mass of catch cup to mass of block = 0.006 / 0.009 = 0.67
For metal:
Change in mass of spout cup = 0.115
Change in mass of catch cup = 0.019
Mass of block = 0.132
Ratio of Change in mass of spout cup to mass of block = 0.115 / 0.132 = 0.87
Ratio of Change in mass of catch cup to mass of block = 0.019 / 0.132 = 0.14
From the above, the mathematical relationship is
Mass of block = Change in mass of spout cup + Change in mass of catch cup
2)
We notice that the ratio of change in mass in spout cup to mass of block is 3.95 times higher for metal block compared to wooden block (0.87 / 0.22 = 3.95)
This is because density of metal is much higher compared to wood. Therefore it displaces much less water.
3)
% difference = (0.009 - 0.006) / 0.009 * 100 = 33.3 %
4)
Buoyant force on wooden block = 0.006*g = 0.006*9.81 = 0.05886 N
Buoyant force on metal block = 0.019*g = 0.019*9.81 = 0.18639 N
For wood, Ratio of Buoyant force to weight of block = 0.05886 / 0.0882 = 0.667
For metal, Ratio of Buoyant force to weight of block = 0.18639 / 1.2936 = 0.144
Wooden block was floating, because it had lower density than water.
Metal block sank, because it had higher density than water.
For an object to float, its density should be lighter than the fluid density.