# Energy could be defined as the capacity to do work

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Energy could be defined as the “capacity to do work.” And, in fact, the two are intrinsically related and thus have the same units. The SI units we will try to use most is the Joule, J (=kg m 2 s -2 ).

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ESM120: Global Environmental Interactions Houlton Winter 2015 How much is 1 Joule? About a heartbeat. How much is a Snickers Bar? Dietary “calories” are really scientific kilocalories, which is 4.19 kJ. So, a 275 “calorie” candy bar can yield 1.15 MJ of energy, equivalent to freezing 3.4 kg water, and a 2500 calories (per day) diet is 10 MJ . 1 gallon of gas ~ 120 MJ. In many instances it’s not the amount, but the amount per time (like Snickers per day) that is important. For energy this is power , having units of W (=Js -1 ). How much is a Watt? Human metabolism (at rest) is ~75 W. Laptop ~50 W. Hairdryer ~1.5 kW. Average household ~ 1 kW. US total ~3.9 Terawatts (TW=10 12 W). Hurricane ~100 TW. Energy budgeting – (convert to Joules) Radiant Energy : transferred by electromagnetic waves, which propagate through a vacuum, not heating the region between Heat Capacity , C p : energy required to raise given mass of substance by a certain temperature (ratio of energy absorbed:temperature increase). C p water = 4.18 kJ degree -1 kg -1 ; C p quartz/soil ~ 0.8 ; C p air ~ 1.0 Latent Heat : energy required to change a substance s phase L E (evaporation) water = 2,260 kJ kg -1 L M (melting) water = 335 kJ kg -1 Sensible Heat : energy that may be perceived by touch, proportional to temperature ESM120: Global Environmental Interactions Houlton Winter 2015 Heat Capacity Differences
ESM120: Global Environmental Interactions Houlton Winter 2015 ESM120: Global Environmental Interactions Houlton Winter 2015 The “Find the Continents” Game!

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• Winter '16
• Energy, atmospheric circulation, Global Environmental Interactions

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