what is the idea in newtons law of cooling?

Answer 1

Newton's law of cooling says that if you have a hot brick and you take it outside and put it in the snow, it will cool off faster than if you have a similar hot brick and leave it in a warm room.

More specifically, it is a mathematical formula that gives an idea of just how MUCH faster Brick 1 will cool than Brick 2. The law says that the brick's rate of cooling is proportional to the temperature difference between the brick and its surroundings.

Specific example:

Say the brick's temperature is 100°, and the surrounding temperature is 80°. That's a temperature difference of 20°. And suppose we do measurements and find that the brick cools off at a rate of 1 degree every 10 minutes.

Next, take a 100° brick and put it in a colder room which is only 60°. This time the temperature difference is twice as much as before (40°). Newton's law of cooling says that, in this case, the brick should cool off twice as fast; that is, it should cool off at a rate of 2 degrees every 10 minutes.

I've used "bricks" in this example, but of course Newton's law applies to all objects, not just bricks. Also, Newton's law doesn't say exactly how fast (degrees per minute) any given object will cool off (that depends also on the object's size, shape and composition). The law just says how the rate of cooling will change according to how the temperature difference changes.