In the old days, on a cold winter night it was common to bring a hot object to bed with you. Which would be better to keep you warm through the cold night - a 10 kg iron brick or a 10 kg jug of hot water at the same temperature?
10 kg iron brick
10 kg jug of hot water
WHY?!!
A 10 kg jug of hot water would be better for keeping you warm through the cold night compared to a 10 kg iron brick.
The reason is that water has a higher specific heat capacity than iron. Specific heat capacity is a measure of how much heat energy a substance can absorb or release without changing its temperature. Water has a specific heat capacity of around 4.18 J/g°C, while iron has a specific heat capacity of only around 0.45 J/g°C.
So, when the jug of hot water is at the same temperature as the iron brick, it will contain much more thermal energy (heat) compared to the brick. This means that the hot water jug can release more heat into the surrounding environment, including your bed, and keep you warmer for a longer time.
Additionally, water is a better conductor of heat than iron. This means that the hot water will transfer its heat to your body more efficiently than the iron brick. Therefore, the 10 kg jug of hot water would be a better choice for keeping you warm through the cold night.
To determine which object would be better at keeping you warm through the cold night, we need to consider their thermal properties and their ability to retain heat.
The 10 kg iron brick and the 10 kg jug of hot water have the same mass, but they differ in their specific heat capacities and temperatures.
Specific heat capacity is the amount of heat energy required to raise the temperature of a given substance by a certain amount. Water has a higher specific heat capacity than iron, which means it can retain heat more effectively. This is why water is often used in heating systems and hot water bottles.
Assuming both the iron brick and the hot water are initially at the same high temperature, the hot water will gradually lose heat to the surroundings during the night. However, since water has a higher specific heat capacity, it will retain more heat for a longer period compared to the iron brick.
Additionally, water has a higher thermal conductivity than iron. Thermal conductivity refers to the ability of a substance to conduct heat. This means that even if the jug of hot water loses some heat to the surrounding air, it can quickly transfer heat to your body, making you feel warmer.
Therefore, in this case, a 10 kg jug of hot water at the same temperature would be better at keeping you warm through the cold night compared to a 10 kg iron brick.
Heat Movement
Thermal energy is always moving. No matter what substance is heated, there is always another place for the heat to move, unless all available substances are the same temperature and equilibrium is reached. This is particularly true on earth, where thermal energy is concentrated in specific places, although some substances manage to hold onto their heat longer than others. Substances of similar temperatures will exchange heat more sluggishly, while substances with a large temperature difference, such as the air and fire, will exchange heat very quickly. Some substances can hold onto heat longer than others. Water, for instance, holds heat for longer periods than metal. (eHow)
Emissivity of iron is .91-.96, while the emissivity of water is 0.98, thus holding onto it's latent heat longer than iron.