Thermodynamics B/C

[BasuSiddha23]

I find it annoying how they say the water temperature is say 70 C but when it ends up in our beaker it has dropped to 55 C. Anyone got a way to combat this problem or it pointless as it is most likely a event supervisor run problem?

As the others have pointed out, there is no way for the event to be run without any discrepancies, so it is not always going to be your fault. Always measure the temperature after the water is poured in, and make sure that your formulas that you use to predict the temperature is changed in accordance to Newton's cooling curve law. I'm sure you can do the math

Okay thanks its nice to know I am not the only one struggling.

What we did at our invitationals was bring a thermometer to measure the temperatures ourselves.

Also, we tried using Newton's Law of Cooling for predictions, and when we did this, it was off by many degrees. Am I doing something wrong or is everyone having this problem?

[UTF-8 U+6211 U+662F]

As the others have pointed out, there is no way for the event to be run without any discrepancies, so it is not always going to be your fault. Always measure the temperature after the water is poured in, and make sure that your formulas that you use to predict the temperature is changed in accordance to Newton's cooling curve law. I'm sure you can do the math

Okay thanks its nice to know I am not the only one struggling.

What we did at our invitationals was bring a thermometer to measure the temperatures ourselves.

Also, we tried using Newton's Law of Cooling for predictions, and when we did this, it was off by many degrees. Am I doing something wrong or is everyone having this problem?

Newton's law of cooling is a theoretical model, and doesn't account for factors like steam being trapped in the box or thermal conductivity that changes depending on temperature. Therefore, you can't rely on it alone (this is why the graphs are helpful!).

[Alex-RCHS]

As the others have pointed out, there is no way for the event to be run without any discrepancies, so it is not always going to be your fault. Always measure the temperature after the water is poured in, and make sure that your formulas that you use to predict the temperature is changed in accordance to Newton's cooling curve law. I'm sure you can do the math

Okay thanks its nice to know I am not the only one struggling.

What we did at our invitationals was bring a thermometer to measure the temperatures ourselves.

Also, we tried using Newton's Law of Cooling for predictions, and when we did this, it was off by many degrees. Am I doing something wrong or is everyone having this problem?

I have not tried using Newton's Law of Cooling to predict temperature but I can tell you with certainty that the setup for thermo is far more complex than Newton's Law of Cooling is able to predict. Other factors such as evaporation, condensation, convection, the varying thermal properties of the materials of your beaker and device, etc., play important roles.

[kendreaditya]

Okay thanks its nice to know I am not the only one struggling.

What we did at our invitationals was bring a thermometer to measure the temperatures ourselves.

Also, we tried using Newton's Law of Cooling for predictions, and when we did this, it was off by many degrees. Am I doing something wrong or is everyone having this problem?

I have not tried using Newton's Law of Cooling to predict temperature but I can tell you with certainty that the setup for thermo is far more complex than Newton's Law of Cooling is able to predict. Other factors such as evaporation, condensation, convection, the varying thermal properties of the materials of your beaker and device, etc., play important roles.

Newton's Law creates a constant (k) for the device that is used in the equation to predict the temperature. As a result, those factors that you have mentioned earlier are accounted for in the constant.

The equations for Newton's Law of Cooling is T(t) = Ts +(T0 - Ts)e^(-kt)

where:
t = time taken for the cooling
T(t) = the temperature of the given object at time t
Ts= the surrounding temperature
T0 = the initial temperature of the object
k = decay constant

[Justin72835]

What we did at our invitationals was bring a thermometer to measure the temperatures ourselves.

Also, we tried using Newton's Law of Cooling for predictions, and when we did this, it was off by many degrees. Am I doing something wrong or is everyone having this problem?

I have not tried using Newton's Law of Cooling to predict temperature but I can tell you with certainty that the setup for thermo is far more complex than Newton's Law of Cooling is able to predict. Other factors such as evaporation, condensation, convection, the varying thermal properties of the materials of your beaker and device, etc., play important roles.

Newton's Law creates a constant (k) for the device that is used in the equation to predict the temperature. As a result, those factors that you have mentioned earlier are accounted for in the constant.

The equations for Newton's Law of Cooling is T(t) = Ts +(T0 - Ts)e^(-kt)

where:
t = time taken for the cooling
T(t) = the temperature of the given object at time t
Ts= the surrounding temperature
T0 = the initial temperature of the object
k = decay constant

One thing that Newton's Law of Cooling doesn't account for is the extreme drop in temperature when you first place the beaker in. After about two minutes, the water settles into Newton's Law of Cooling but by then the temperature has dropped a significant amount.

[kendreaditya]

Has anyone tested how much the ambient temperature or humidity effects the device's internal beaker temperature?

[kendreaditya]

One thing that Newton's Law of Cooling doesn't account for is the extreme drop in temperature when you first place the beaker in. After about two minutes, the water settles into Newton's Law of Cooling but by then the temperature has dropped a significant amount.

But Siddha had measured the temperature after the water was poured into the beaker, so it must have been something else.

[Justin72835]

One thing that Newton's Law of Cooling doesn't account for is the extreme drop in temperature when you first place the beaker in. After about two minutes, the water settles into Newton's Law of Cooling but by then the temperature has dropped a significant amount.

But Siddha had measured the temperature after the water was poured into the beaker, so it must have been something else.

Rip, I guess I should've read the previous posts before commenting

[kendreaditya]

One thing that Newton's Law of Cooling doesn't account for is the extreme drop in temperature when you first place the beaker in. After about two minutes, the water settles into Newton's Law of Cooling but by then the temperature has dropped a significant amount.

But Siddha had measured the temperature after the water was poured into the beaker, so it must have been something else.

Rip, I guess I should've read the previous posts before commenting

Its fine, you helped, and that's what counts

Based on this article (https://www.quora.com/Whats-wrong-with- ... of-cooling), I guess surface radiative losses are highly nonlinear, according to Stefan–Boltzmann law (https://en.wikipedia.org/wiki/Stefan%E2 ... tzmann_law).

[Galahad]

Okay thanks its nice to know I am not the only one struggling.

What we did at our invitationals was bring a thermometer to measure the temperatures ourselves.

Also, we tried using Newton's Law of Cooling for predictions, and when we did this, it was off by many degrees. Am I doing something wrong or is everyone having this problem?

Newton's law of cooling is a theoretical model, and doesn't account for factors like steam being trapped in the box or thermal conductivity that changes depending on temperature. Therefore, you can't rely on it alone (this is why the graphs are helpful!).

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