10.1 A Closer Look at the Sun Our Goals for Learning Why does the Sun shine? What is the Sun’s structure?

Why does the Sun shine?

Is it on FIRE?

Is it on FIRE? Chemical Energy Content ~ 10,000 years Luminosity

Is it on FIRE? … NO! Chemical Energy Content ~ 10,000 years Luminosity

Is it CONTRACTING?

Is it CONTRACTING? Gravitational Potential Energy ~ 25 million years Luminosity

Is it CONTRACTING? … NO! Gravitational Potential Energy ~ 25 million years Luminosity

E = mc2 - Einstein, 1905 Is it CONTRACTING? … NO! Gravitational Potential Energy ~ 25 million years Luminosity

Is it powered by NUCLEAR ENERGY? Nuclear Potential Energy (core) ~ 10 billion years Luminosity

Is it powered by NUCLEAR ENERGY? … YES! Nuclear Potential Energy (core) ~ 10 billion years Luminosity

Gravitational contraction: Provided energy that heated core as Sun was forming Contraction stopped when fusion began

Weight of upper layers compresses lower layers

Gravitational equilibrium: The outward push of pressure balances the inward pull of gravity

Gravitational equilibrium: Energy provided by fusion maintains the pressure

What have we learned? Why does the Sun shine? The Sun shines because gravitational equilibrium (pressure balancing gravity) keeps its core hot and dense enough to release energy through nuclear fusion.

Do Activity #30 (pages 103-105), Questions 8 through 16 …then we’ll have a clicker quiz

8. In which three stars (or balloons) in Figure 4 are the particles moving slowest? (30 seconds to answer) A B C All three have same speed of particles :00

9. Which star in Figure 4 has the highest temperature? Star A Star B Star C :00

10. If you cool down a rubber balloon in a fridge, what will happen to it? (45 sec) It will shrink, because lower temperature means less pressure to resist the inward pull of the rubber It will shrink because lower temperature means less volume Nothing will happen except it will feel colder :00

11. If a star cools, it shrinks because: Lower temperature means less volume Fusion reactions which occur at a lower temperature convert less mass into energy Lower temperature means less pressure to resist gravity :00

12. If the rate of hydrogen fusion in a star were to increase slightly, what would happen to the star? It would expand It would contract Nothing :00

13. When you expend energy to blow up a balloon, where does that energy go? Mostly into heating the air in the balloon Mostly into elastic energy stored in the material of the balloon Nowhere – energy is conserved :00