Chapter 10: Section 2

 Describe the First Law of Thermodynamics  Make calculations involving changes in internal energy  Create and analyze energy transfer diagrams

 I magine a roller coaster that operates on a frictionless track  Work, a force that causes a displacement, is initially necessary to raise the car against the gravitational force. ◦ Once the car is freely moving, it will have a certain kinetic and potential energy  With no friction, the mechanical energy (KE + PE) will remain constant

 If friction is taken into account, mechanical energy is no longer conserved  A steady decrease in the coaster’s total mechanical energy occurs because of work being done against friction

 Mechanical energy is transferred to particles throughout the entire coaster ◦ The increases in internal energy equal the decreases in mechanical energy  Most of this energy is gradually lost to the air as heat ◦ If the internal energy of the roller coaster and the energy dissipated to the surrounding air are taken into account, the total energy will be constant

 The principle of energy conservation that takes into account internal energy as well as work and heat is called the First Law of Thermodynamics  The First Law says that energy cannot be created nor destroyed.

 In terms of a machine, this means that the total energy output (work done by the machine) is equal to the heat supplied.  In other words, the change in the internal energy of a closed system is equal to the heat added to the system minus the work done by the system. ◦ If all of the heat supplied to the system (Q) is transformed into work (W), then the change in total internal energy should be zero

∆U = Q – W  Because the system operates in the real world, some energy always escapes into the outside world

 A total of 135 J of work is done on a gaseous refrigerant as it undergoes compression. If the internal energy of the gas increases by 114 J during the process, what is the total amount of energy transferred as heat? Has energy been added to or removed from the refrigerant as heat? ◦ -21 J ◦ Energy is removed

 Energy transfer diagrams show the locations of energy stores and energy transfers.  For example, consider the energy transfers in a simple electrical circuit.

 The battery is a store of chemical energy.  The energy is transferred by electricity to the lamp, which transfers the energy to the surroundings by light.