III.PHYSICAL PRINCIPALS - TERMINOLOGY A. Temperature and Heat 1. Temperature Intensity of Energy Units; Degrees C or F

–Heat (energy) Capacity to work BTU (British Thermal Unit)- energy to raise temperature of one pound (2 cups) of water 1°F Calorie- energy to Raise temperature of one gram of water 1 0 C

2.Heat Transfer –Heat moving due to temperature difference a. Conduction Heat transfer from touching objects Energy moves from high to low temperature Examples : –Touching cold or hot surface –Metal spoon in boiling water –Heat loss through greenhouse covering

b. Convection Transfer from surface to moving air or water 1) Forced convection –Examples Fan blows air over warm surface Wind blows over black driveway

2)Natural convection Hot air (less dense) rises, replaced by cooler air (more dense) Examples: –Hot air rises from black driveway –Air rising from hot pipe in greenhouse Warm airCool air

c.Radiation All surfaces emit energy Energy moves from high to low temperature Requires no air, water etc. between objects - transfer better in vacuum Examples: –Two people –Person and building –Person and clear sky –Objects in greenhouse & clear sky

B.Relative Humidity 1.Definition % RH = Amount of moisture in air divided by the Maximum amount of moisture air can hold at temp. x Effect of Temperature As air temperature increases air can hold more moisture

4.Evaporation –Requires 1060 BTU to convert 1 lb (2 cups) of H 2 O from liquid to vapor 5.Condensation –Moisture in the vapor form is converted to a liquid –air cools below dew point condensation occurs