Thermal Physics Lesson 3.1 3.1.3 State that the internal energy of a substance is the total potential energy and random kinetic energy of the molecules of the substance. 3.1.4 Explain and distinguish between the macroscopic concepts of temperature, internal energy and thermal energy (heat). 3.2.12 Explain the macroscopic behaviour of an ideal gas in terms of a molecular model.

Need to know Only qualitative explanations are required. Students should, for example, be able to explain how a change in volume results in a change in the frequency of particle collisions with the container and how this relates to a change in pressure and/or temperature

Moving molecules The kinetic energy of the molecules arises from their random/translational and rotational motion. Potential energy of the molecules arises from the forces between the molecules. Internal energy is the total K.E and P.E of the particles in an object. Temperature is a measure of the average kinetic energy of the particles. Thermal energy refers to the non-mechanical transfer of energy between a system and its surroundings. In this respect it is just as incorrect to refer to the “thermal energy in a body” as it would be to refer to the “work in a body”.

Brownian motion and what this tells us about air (and other gases) Matter is made up of particles (molecules and atoms). These particles are in constant motion i.e. They have kinetic energy. Evidence includes the combination laws of gases, and Brownian motion.

Boyle’s law Boyle’s law (PV = constant at constant temperature). You pump air in to pressurise the oil, which compresses an air space at the top. A series of about 10 P and V readings usually gives a good fit to a straight line when P is plotted against 1/V. http://chem.salve.edu/chemistry/ boyle.asp P trapped air oil pump

Boyles law demo Draw a diagram of the alternative apparatus. Plot a graph of p vs V Plot a graph of p vs 1/V Draw a conclusion Explain your findings in terms of the particles in the gas

To do - extension Read p 290 Answer q 1 p291 Answer q 7 p 317 a&b i-iii Challenge can you do part iv – this is not on your syllabus