# Cooling Rate of Water Essay

1264 Words Aug 13th, 2013 6 Pages
Newton’s Law of Cooling

The main purpose of this experiment was to find the positive constant “K” for different liquids in the Newton’s Law of Cooling equation, in order to determine when it was safe to store food products in commercial restaurant after cooking. The high risk temperature for bacteria growth is between 5 and 60 degrees. However putting hot food into your fridge before this point can cause food poisoning especially in deep containers, which is why it is vital that food companies and chiefs are aware of how longer a food, takes to cool down from an approximate temperature. Obviously an exact value is impossible because of varying variables e.g. room temperature, depth of container etc. However by applying newton’s laws you
This law, mostly referred to as Newton’s law of cooling, which states that the rate of cooling of a body is directly proportional to the difference of temperature of the body and the surrounding. It implies that the body will loose heat faster initially, as the difference between the temperature of the body and that of the surrounding will be high, but that rate of heat loss will keep decreasing as the temperature of the body decreases. When the medium into which the hot body is placed varies beyond a simple fluid, such as in the case of a gas, solid, or vacuum, etc., this becomes a residual effect requiring further analysis. [5]

In mathematic terms, the cooling rate is equal to the temperature difference between the two objects, multiplied by a material constant. The cooling rate has units of degrees/unit-time, thus the constant has units of 1/unit-time. The equation is shown below.

Cooling rate =
This is called Newton's law of cooling. It is an empirical law and there are conditions under which it does not hold. The rate constant σ depends on physical properties of the system. such as its mass, specific heat capacity, surface area, etc. Newton's law of cooling can be rewritten as dΔT /ΔT = -kdt and integrated to With:
= The water’s temperature at a given time, t
The initial temperature difference and
The air temperature
Thus, the temperature of any body approaches exponentially to the temperature of the surrounding

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