Chapter 6 Power

Chapter 6.1 Power in Mechanical Systems

Power Power is the amount of work done in a certain amount of time. In other words, power is the rate at which work is done.Power is the amount of work done in a certain amount of time. In other words, power is the rate at which work is done.

Calculating Power Power can be calculated using the following formulas:Power can be calculated using the following formulas: –Power (P) = Work (W)/Time (t) P = W/t –Power (P) = Energy (E)/Time(t) P = E/t –Units: Energy or Work – Joules (J)Energy or Work – Joules (J) Time – seconds (s)Time – seconds (s) Power – Watts (W) 1 WPower – Watts (W) 1 W 1 W is Equal to 1 J/sNOTE: J/s is NOT the unit for power!1 W is Equal to 1 J/s NOTE: J/s is NOT the unit for power!

Calculating Power Power can also be measured in kilowatts. The watt is such a small amount of power that many times kilowatts are used instead.Power can also be measured in kilowatts. The watt is such a small amount of power that many times kilowatts are used instead. 1 kW = 1000 watts1 kW = 1000 watts Another common measurement for power is horsepower (hp).Another common measurement for power is horsepower (hp). 1 hp = 746 W1 hp = 746 W

Chapter 6.3 Power in Electrical Systems

Electrical Power Electrical power is the rate at which electrical energy is converted into other forms of energy. P = I x VElectrical power is the rate at which electrical energy is converted into other forms of energy. P = I x V Units:Units: –Power – watts (W) –Current – Amperes (A) –Voltage difference – Volts (V)

Energy and Appliances To calculate the amount of electrical energy used by an appliance, multiply the power used times the time the appliance is used.To calculate the amount of electrical energy used by an appliance, multiply the power used times the time the appliance is used. E = P x t E = P x tUnits: Electrical energy – kilowatt-hour (kWh)Electrical energy – kilowatt-hour (kWh) Power – watts (W)Power – watts (W) Time – hours (h)Time – hours (h)

Energy and Appliances - 1 A kilowatt-hour (kWh) is the energy consumed by a 1 kW device operated continuously for 1 hour.A kilowatt-hour (kWh) is the energy consumed by a 1 kW device operated continuously for 1 hour. The equation E = P x t is part of the method the electric company uses to calculate your electric bill.The equation E = P x t is part of the method the electric company uses to calculate your electric bill. To calculate your bill, the number of kWh used is multiplied by how much the power company is charging per kWh.To calculate your bill, the number of kWh used is multiplied by how much the power company is charging per kWh.

Energy and Appliances - 2 For example, if your electric company charges 12 cents ($0.12) per kWh and you used 1,375 kW of electricity during the month, then your electricity would cost you $ For example, if your electric company charges 12 cents ($0.12) per kWh and you used 1,375 kW of electricity during the month, then your electricity would cost you $ Total Cost = Energy (E) x Cost per kWhTotal Cost = Energy (E) x Cost per kWh = 1,375 x $0.12 = 1,375 x $0.12 = $ = $ Power companies add other fees such as fuel Power companies add other fees such as fuel cost to this total, so your bill would actually be cost to this total, so your bill would actually be more than just the cost of the electricity. more than just the cost of the electricity.