# PENDULUM QUESTIONS :surprised

1. Dec 12, 2004

### Science_and_math

Grandfather clocks with brass pendulums tend to be very sensitive to changes in temperature.
1. WHY?
2. What can be done to overcome this?

2. Dec 12, 2004

### Norman

how does the coefficient of expansion for brass compare to that of other metals say?

3. Dec 20, 2004

### rayjohn01

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

4. Dec 21, 2004

### bionic_atom

If I had to take a guess I would say the specific heat of that with the brass.

5. Dec 22, 2004

### rayjohn01

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

6. Dec 22, 2004

### Norman

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

7. Dec 22, 2004

### FredGarvin

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).