How does temperature affect grandfather clocks with brass pendulums?

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Discussion Overview

The discussion centers on the effects of temperature on grandfather clocks that utilize brass pendulums, exploring the underlying mechanisms of thermal expansion and potential compensation methods. Participants examine the relationship between temperature changes and the performance of these clocks, with a focus on theoretical and practical implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Historical

Main Points Raised

  • Some participants note that grandfather clocks with brass pendulums are sensitive to temperature changes due to the thermal expansion of brass.
  • One participant questions how the coefficient of expansion for brass compares to that of other metals.
  • Another participant explains that pendulums change their period because their length varies with temperature, which is directly related to the metal's expansion coefficients.
  • Compensation methods for maintaining pendulum accuracy may involve innovative designs that keep the effective mass at a constant distance from the fulcrum, potentially using materials with different coefficients of expansion.
  • A participant suggests that specific heat may play a role, although this is challenged by others who clarify that specific heat and thermal expansion are distinct properties.
  • Historical context is provided regarding the development of accurate clocks, mentioning John Harrison's contributions and the challenges faced with pendulums on ships.
  • Participants discuss the coefficient of linear expansion for brass, noting it as approximately 10.4 x 10^-6 in/in °F, and compare it to that of unalloyed iron.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of specific heat in relation to thermal expansion, with some asserting it is not a factor. The discussion remains unresolved regarding the best methods for compensating for temperature effects on pendulum clocks.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the relationship between specific heat and thermal expansion, as well as the historical accuracy of claims about early clock designs.

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Grandfather clocks with brass pendulums tend to be very sensitive to changes in temperature.
1. WHY?
2. What can be done to overcome this?
 
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how does the coefficient of expansion for brass compare to that of other metals say?
 
compensation

Pendulums change period because their length changes with temperature
due directly to metal expansion coefficients.
Compensation methods involve keeping the length at which the effective mass swings at a constant distance from the fulcrum this generally requires a lot of ingenuity and can involve materials with different coefficients .
Ray
 
If I had to take a guess I would say the specific heat of that with the brass.
 
To bionic -- specific heat is not the same as expansion
To Norm -- you can always look this up on the internet as 'physical constants'
To all -- the history of clocks is fascinating and I think that the first accurate clock was created in a competition to make a navigation aid on board ships -- this was not a pendulum but it did incorporate various compensation means for temperature and motion -- sorry for the moment I cannot recall the inventor -- very famous , but I am sure you can search this if interested.
Ray
 
rayjohn01 said:
To Norm -- you can always look this up on the internet as 'physical constants'.

The question I posed was to help the original poster think about what is going on with the pendulum. Typically on this forum you have a lot of students asking questions about homework. It is always best to try and lead them to an answer through posing related question they can answer along the way to the solution instead of just telling them the answer. Students tend to remember solving a problem better when they figure them out on their own compared to being given an answer.
Cheers,
Norm
 
Rayjohn01, the person you are thinking about is John Harrison of England. He invented his clocks in the cause to solve the longitude problem of the day. As far as I know they were spring driven since pendulums on rocking ships did not work well at all.

The alpha for brass is about 10.4 x 10^-6 in/in °F. Compare that to the alpha for un alloyed iron at 6.7 x 10^-6 in/in °F.

Specific heat of the material is not a factor (as was stated before).
 

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