Why Do Tension Measurements Differ in Bicycle Incline Experiments?

[brianinbwangju]

Homework Statement

About a year ago I prepared a test for a bicycle on an inclined plane by:
tying down the handlebars, so they wouldn't move much
removing the chain
and tying a wire to a tension scale and the bicycle in 2 ways.
1. I attached a wire to the rear wheel and the scale, and attached another wire from the scale to a rack at the rear of the bike.
2. I attached one end of a wire to the point on the front wheel where it touches the ground and the other end to a chain, wrapped the chain around a sprocket on the bottom bracket, attached the other end of the chain to the tension scale, and attached a wire from the tension scale to the front forks.
see attachment
If the measurement for 1 is 3 kg, what will be the measurement for 2?

Homework Equations

T=rF

The Attempt at a Solution

From bicycle vs. pulley, part 1 https://www.physicsforums.com/showthread.php?t=148577
measurement 1 of about 3 kg can be calculated.

from what I learned from bicycle vs. pulley, part 2https://www.physicsforums.com/showthread.php?t=148808
I can make the following calculation:
A ground force of 3 kg is opposed by 3 kg of tension along the wire from the front wheel to the sprocket. 3 kg of torque on the sprocket creates 3 kg of tension along the wire from the sprocket to the front fenders. In other words, both measurements should be the same - about 3 kg.
However, measurement 1 was about 3 kg, but measurements for 2 were from 2 kg to 2.7 kg.
So, why weren't they the same? Is there any explanantion besides a faulty test?

 

[anathema]

Thank you for sharing your experiment with us. It seems like you have put a lot of thought and effort into setting up your test for the bicycle on an inclined plane. Based on the information you provided, it is possible that there are a few factors that could have affected the difference in measurements between 1 and 2.

Firstly, the method of attaching the tension scale to the bicycle may have caused some discrepancies. In the first method, the wire was attached to the rear wheel and a rack at the rear of the bike. This may have caused the bike to tilt slightly, altering the angle of the inclined plane and affecting the measurement. In the second method, the wire was attached to the front wheel and the tension scale, which may have provided a more stable and accurate measurement.

Additionally, the weight distribution of the bike may have played a role. In the first method, the weight of the bike was mainly concentrated at the rear, where the tension scale was attached. This could have caused more tension in the wire and a higher measurement. In the second method, the weight was distributed more evenly between the front and rear of the bike, potentially resulting in a lower measurement.

Furthermore, the presence of the chain in the second method may have also affected the measurement. The chain may have added additional tension and resistance, leading to a lower measurement compared to the first method where the chain was removed.

Overall, it is important to carefully consider all the variables and potential sources of error when conducting experiments. It is possible that a combination of factors contributed to the difference in measurements between the two methods. I hope this explanation helps to clarify the results of your experiment. Keep up the good work in your scientific endeavors!

 

[m2003]

I would like to commend you on your experiment design and the use of multiple methods to measure the forces involved in the bicycle on an inclined plane. Your calculations and understanding of the forces involved are also impressive.

To address your question, there could be a few possible explanations for the discrepancy in measurements between method 1 and method 2. One possibility is that there may have been some friction or resistance in the chain or sprocket that could have affected the tension measurements. Another possibility is that the tension scale itself may not have been perfectly calibrated or may have had some error in its readings. Additionally, the placement of the wires and their angles may have also influenced the tension measurements.

To determine the exact cause of the discrepancy, I would recommend repeating the experiment multiple times and taking careful note of any potential sources of error. This could include checking the calibration of the tension scale, ensuring that the chain and sprocket are free of resistance, and carefully measuring the angles and placement of the wires. By conducting multiple trials and controlling for these factors, you may be able to achieve more consistent results and potentially identify the source of the discrepancy.

Overall, it is important to always consider potential sources of error and to repeat experiments multiple times to ensure the accuracy and reliability of your results. Keep up the good work in your scientific endeavors!