Introduction to SAT II Physics - FreeExamPapers

10. B
Kepler’s Third Law tells us that T 2 /a 3 is a constant for every planet in a system. If we let xT be the value
for the period of planet B ’s orbit, then we can solve for x using a bit of algebra:
Thermal Physics
THERMAL PHYSICS IS ESSENTIALLY THE study of heat, temperature, and heat transfer.
As we shall see—particularly when we look at the Second Law of Thermodynamics—these
concepts have a far broader range of application than you may at first imagine. All of these
concepts are closely related to thermal energy, which is one of the most important forms of
energy. In almost every energy transformation, some thermal energy is produced in the form of
heat. To take an example that by now should be familiar, friction produces heat. Rub your hands
briskly together and you’ll feel heat produced by friction.
When you slide a book along a table, the book will not remain in motion, as Newton’s First Law
would lead us to expect, because friction between the book and the table causes the book to slow
down and stop. As the velocity of the book decreases, so does its kinetic energy, but this decrease
is not a startling violation of the law of conservation of energy. Rather, the kinetic energy of the
book is slowly transformed into thermal energy. Because friction acts over a relatively large
distance, neither the table nor the book will be noticeably warmer. However, if you were somehow
able to measure the heat produced through friction, you would find that the total heat produced in
bringing the book to a stop is equal to the book’s initial kinetic energy.
Technically speaking, thermal energy is the energy associated with the random vibration and
movement of molecules. All matter consists of trillions of trillions of tiny molecules, none of
which are entirely still. The degree to which they move determines the amount of thermal energy
in an object.
While thermal energy comes into play in a wide range of phenomena, SAT II Physics will focus
primarily on the sorts of things you might associate with words like heat and temperature. We’ll
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