Physics help is provided to university, college, and high school students by expert physics tutors. Physics homework help, tutorials, solved problem sets are also available.
For physics help see our physics homework help section or our physics tutor directory.

Physics Help » Physics Tutorial Index »

Physics Tutorial: Newton's Law of Cooling and Coffee

Newton’s Law of cooling states that a hot object transfers heat to its surroundings (cools) at a rate proportional to the difference in temperature between the two.

 

Newton’s Law of cooling means that if a hot object is subjected to a very cold object, it will transfer its heat a lot faster than if the hot object that is subjected to a mildly cool object.

 

Measurements of liquids cooling confirm Newton's Law of Cooling. You are having dinner with your friend at a restaurant one evening. You place your order, and the waitress brings you your coffee much earlier than the rest of your meal. You want the coffee to stay hot until your food arrives so you can have them at the same time. You always add cream to your coffee, but know that from Newton’s Law of Cooling that a hot object transfers heat to its surroundings at a rate proportional to the difference in temperature between the two. So your choice is to either add the cream to your coffee now, or add the cream to your coffee once your meal arrives. You think about the problem for a moment and come to a conclusion.

 

If you add the cream right away the temperature difference between the coffee and its surrounding air is brought closer together than between just the hot coffee without cream and restaurant air. A hot object cools at a rate that is faster when the difference between the temperatures of liquid and the surrounding air and cup is the greatest. Adding cool cream at the beginning slows down the cooling speed because it decreases the difference in temperature between the hot coffee and its surroundings. If you did not add cream right away the difference in temperatures of the hot coffee and restaurant air and cup is the greatest, so it would cool more rapidly and then when the cream would be added, it would cool even further. You add your cream to your coffee as soon you got it,and enjoy a nice hot cup of coffee when your meal arrives all thanks to Newton’s Law of Cooling to help you out.

 

Graph of temperature data for liquids confirm Newton's Law of Cooling.Question – What is another food that Newton’s Law of Cooling can be applied to, to make consuming it more pleasant?

 

Answer – Newton’s Law of Cooling can be applied to a hot bowl of soup that you enjoy eating together with a sandwich. You enjoy adding a liquid spice flavor called “Maggi” – but do not know if you should add it before your sandwich arrives or after. By applying Newton’s Law of Cooling, you should add it before, so your soup is still nice and warm when your sandwich arrives.

 

more thermodynamics problems

 

For help with physics problems, try

Physics Homework Help


- Gregory Shepertycky