First and Second Laws of Thermodynamics

First Law of Thermodynamics

What is the zeroth law of thermodynamics?

Zeroth Law

• Objects in Contact with one another have the same temperature if they are in thermal equilibrium. Nothing else matters

Discussion

A book is pushed across a table. It slows to a stop is energy lost? Why or why not?

Work affects energy

• E= final thermal energy

• initial thermal energy - work= E_i - W= E_f

• E_f- E_i= -W

• Thermal energy decreases when work is done by a system

• Thermal energy increases when work is done on a system

1st law of Thermodynamics

• Conservation law

• change in thermal energy= heat -work

•  $\Delta E=Q-W$  

• Heat gained by a system adds thermal energy

• Work done by a system takes away thermal energy

Jogging along the beach one day you do 4.3 x 105 J of work and give off 3.8 x 105 J of heat.

a) What is the change in your internal energy?

b) Switching over to walking, you give off 1.2 x 105 J of heat and your internal energy decreases by 2.6 x 105 J. How much work have you done while walking?

• a) Make sure you use correct signs here it all starts by defining the system

• b) what are we looking for? rearrange our 1st law to solve for it.

Open Ended

A swimmer does 4.3x10⁵ J of work and gives off 1.7x10⁵ J of heat during a workout. Determine ΔE, W, Q for the swimmer.

Go and research an example of thermal energy being transformed to mechanical energy(work). Share it with the class once you have found one. If someone has used your example find another.