ANSWER KEY EXPERIMENT 5: ARCHIMEDES PRINCIPLE

Transcription

1 ANSWER KEY EXPERIMENT 5: ARCHIMEDES PRINCIPLE OBJECTIVE To determine the buoyant force from Archimedes Principle. INFERENCE Archimedes` Principle states that When an object is immersed in a fluid (liquid or gas), the buoyant force (up thrust force) on the object is equal to the weight of fluid displaced by the object. HYPOTHESIS The buoyant force on an object is equal to the weight of the water displaced. APPARATUS Retort stand Spring balance / Balance Set of Block (Wood, Metal, Plastic) Beaker Eureka beaker Scissor String PROCEDURES 1. Weigh the mass of empty beaker. 2. Hang the spring balance at the arm of retort stand. 3. Tie the wooden block and hang to the spring balance. 4. Record the weight of the block in the air as Figure 5a. 5. Fill the Eureka beaker with water. 6. Set the apparatus as Figure 5b. 7. Then, lower the arm of the retort stand tied with the block gently. 8. Let the block arise/sink in water. 9. Record the weight of the block. 10. Water will be displaced from eureka beaker into the other beaker. 11. Record the mass of the displaced water in the beaker. 12. Repeat the above procedures by using the plastic and metal blocks 1

2 1 Procedures Procedures are clearly described in complete and passive sentences. Steps are also numbered. Procedures are clearly described in complete and active sentences. Steps are also numbered. Procedures are stated but difficult to follow. Procedures are partially stated and difficult to follow. Procedures are not stated. DIAGRAM Figure 5a Figure 5b 2 Drawings /Diagrams Clear, accurate diagrams are included. labeled neatly and accurately. included and are labeled. included and partially labeled. included but are not labeled Needed diagrams are missing. 2

3 DATA a. Mass of empty beaker = g Type of Block In the air T 1 (N) Weight of Block (N) In the water T 2 (N) Trial 1 Trial 2 Average Trial 1 Trial 2 Average Mass of beaker with displaced water (g) Weight of Water displace d (N) Significa nt loss of block weight F B = T 1- T 2 Wood Plastic Metal % Error 1. Weight of water = Mass of beaker with displaced water mass of empty beaker. i. Wood = g 95.67g = 95.5g ii. Plastic = g 95.67g = g iii. Metal = g 95.67g = g 2. Convert the answer in gram (g) to kilogram (kg) i. Wood = 95.5 / 1000 = kg ii. Plastic = /1000 = kg iii. Metal = /1000 = kg 3. Convert the answer in kg to Newton ( N ) by multiply 9.81 kg/ms 2 i. Wood = x 9.81 = 0.94 N ii. Plastic = x 9.81 = 1.34 N iii. Metal = x 9.81 = 1.62 N 4. Significant loss of block weight (FB=T1-T2) = Weight of the block in the air, T1 weight of block in the water T2. i. Wood = 1.0N 0.0N= 1.0N ii. Plastic = 1.6N 0.2N = 1.4 N iii. Metal = 4.95 N 3.25 N = 1.7 N 3

4 5. To find the error: Error percentage should be less than 10% Percent Error: ( theoretical - actual / theoretical) x 100 (same as % yield) Significant loss of block weight,fb Weight of water displaced Error (%) = Significant loss of block weight,fb Wood = Plastic = x 100= 6% x 100= 4.28% Metal = x 100= 4.7% 3 Data Presentation of the data in tables or graphs is done correctly and accordingly. Graphs and/or tables are labeled and titled. Accurate presentation of the data in tables or graphs. Graphs and/or tables are not labeled and titled. Accurate presentation of the data in written form, but no graphs or tables is presented. Data are shown but inaccurate. Data are not shown. 4 Calculations All calculations are shown and the results are correct with appropriate units. All calculations are shown and the results are correct without appropriate units. All calculations are shown but not all the results are correct. All calculations are shown but all the results are incorrect calculations are shown. 4

5 ANALYSIS i) An object will float if the buoyant force is greater than the weight of the object. ii) An object will sink if its weight is greater than the buoyant force. iii) From the experiment, metal has a greater buoyant force for it to float. iv) Random error from equipment such as eureka beaker and spring balance. v) Error from student (human error) by using their finger to push the object to immerse in the fluid. 5 Analysis Explain the findings in the experiment. Able to explain experimental errors, their possible effects, and ways to reduce errors. Explain the findings in the experiment. Able to explain experimental errors and their possible effects. Explain very briefly about the findings in experiment. Experimental errors are mentioned. Explain very briefly about the findings in experiment Or only experimental errors are mentioned. analyses are shown. QUESTIONS 1. Why do some objects; a. float when placed in water An object will float if the buoyant force is greater than the weight of the object. b. sink when placed in water An object will sink if its weight is greater than the buoyant force. 2. From the experiment, which block has a greater buoyant force for it to float? From the experiment, metal has a greater buoyant force for it to float. 6 Questions The questions answered are correctly, clearly identified and stated according to the theory. The questions answered in the lab report is identified, but not stated according to the theory. t all the questions are answered. The questions answered in the lab report are irrelevant. The questions are not answered. 5

6 CONCLUSION From the experiment, it is found that when an object is immersed in water, the buoyant force (up thrust force) on the object is equal to the weight of water displaced by the object. 7 included the finding from the experiment and supported the hypothesis / theory. included the finding from the experiment but supported with incorrect hypothesis / theory. included the finding from the experiment but not supported the hypothesis / theory. included but not related to the experiment. conclusion was included in the report. 6