Finding mass of a meter stick using torque

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To find the mass of a meter stick using torque, the fulcrum is placed at the 60 cm mark, with a 100 g mass 30 cm away on one side and a 50 g mass 43 cm away on the other. The net torque must equal zero for the system to be balanced, meaning the torques from the masses and the stick must counterbalance each other. Calculating the torques from the masses yields values that help set up the equation for the torque due to gravity acting on the meter stick. The calculated mass of the meter stick is approximately 85 grams, which is close to the measured value of 97 grams, indicating measurement errors may account for discrepancies. Understanding the relationship between torque, distance from the fulcrum, and the force of gravity is crucial for solving this problem accurately.
  • #31
Nathanael said:
Right, gravity acts everywhere, but it effectively acts on the center of gravity. In other words, if you treat the full force of gravity acting only the center of gravity, then it will be the same as if you treat gravity as being spread across the object. So we can say the force of gravity (9.8 X mass) acts on the center of gravity.I mean the mathematical definition. How is torque defined with numbers? If you know a force, and you know the distance it acts, then what is the torque from that force?

Put this all together and take some time to try to solve the problem.
Torque = rfsintheta but in this problem sintheta=1. I found the torque of gravity to be .0833 from that equation if that's cprrect? So I have .0833 = .1 X f. Solve for f and get f = .833 N. I divide this number by 9.8 to get
 
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  • #32
.085 kg but this can't be right what am I doing wrong?
 
  • #33
khannon5 said:
.085 kg but this can't be right what am I doing wrong?
Good. 85 grams. The actual weight was 97 grams? You're not doing anything wrong. You said it was a lab, right? So you actually measured these distances? That can account for the error.

Look at it like this... If the 50g mass was actually at 42.5 cm and the 100g mass was actually at 30.5 cm, then you would get an answer of 92.5 grams. (Not to mention if the fulcrum is not exactly at 60 cm! That's probably where the error really comes from!)
 
  • #34
Nathanael said:
Good. 85 grams. The actual weight was 97 grams? You're not doing anything wrong. You said it was a lab, right? So you actually measured these distances? That can account for the error.

Look at it like this... If the 50g mass was actually at 42.5 cm and the 100g mass was actually at 30.5 cm, then you would get an answer of 92.5 grams. (Not to mention if the fulcrum is not exactly at 60 cm! That's probably where the error really comes from!)
Ok thank you so much. I really appreciate your time
 

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