Science Buddies: "Ask an Expert"

If I use the equation for heat transfer,Q/A=(T(hot)-T(cold)t/d, will it give me the k (constant) I need to use in Newton's Law of Cooling equation?

Hello rockwalker,

The heat transfer equation you’ve shown relates a temperature change of an object with certain dimensions (area and thickness) to the rate of heat transfer. This equation includes a thermal conductivity value (sometimes denoted as k) that is specific to the object. Some additional information can be found at this site:

http://www.physicsclassroom.com/class/t ... t-Transfer

I’m assuming that the constant (k) that you want is in the equation shown here:

http://www.softschools.com/formulas/phy ... ormula/93/

This equation describes the temperature change of an object as a function of time. The cooling constant (k) is a value that is specific to the object. This is not the same constant that is used in the heat transfer equation. So, you’ll need to find another way to get the constant for the cooling law equation.

I hope this helps. Please post again if you have more questions.

A. Norman

If I come up with the rate for the equation, Rate = k•A•(T1 - T2)/d, for a certain body, is that rate the constant that is used in Newtons law of cooling?

Hi rockwalker,

The equation you posted is for calculating the rate of heat transfer from an object given the object’s dimensions and thermal conductivity. This equation is not useful for finding the constant in the equation for Newton’s law of cooling.

The link I posted previously has an example (#2) showing how you can calculate the constant given some temperature and time data.

http://www.softschools.com/formulas/phy ... ormula/93/

You might want to post some details of your project and how the law of cooling fits in. We may be able to provide better advice with more information.

I hope this helps. Please post again if you have more questions.

A. Norman