1. 4. Intro to Physics III Gravity Fundamental Forces of Nature Part 1 Text: Module 11 pages 255 - 284 Reading Assignments Module 11 pp 255 - 275 Module 11 pp 275 - 284 Homework Assignment Module 11 Study Guide Questions p 283 # 1 - 11 Module 11 Study Guide Questions p 284 # 12 - 23

2. Introduction (p 255) A force is a push or a pull it will cause motions. - F = ma, Relationship to energy and work F x d - Action at a distance versus contact forces

3. Four Fundamental Forces of Nature (p 255) Strong: The strong interaction is very strong, but very short-ranged. It acts only over ranges of order 10-13 centimeters and is responsible for holding the nuclei of atoms together. It is basically attractive, but can be effectively repulsive in some circumstances. Weak: The weak force is responsible for radioactive decay and neutrino interactions. It has a very short range and, as its name indicates, it is very weak. Electromagnetic: The electromagnetic force causes electric and magnetic effects such as the repulsion between like electrical charges or the interaction of bar magnets. It is long-ranged, but much weaker than the strong force. It can be attractive or repulsive, and acts only between pieces of matter carrying electrical charge. Gravitational: The gravitational force is weak, but very long ranged. Furthermore, it is always attractive, and acts between any two pieces of matter in the Universe since mass is its source.

4. The Gravitational Force (in more detail) (p255) - Action at a distance force - all matter attracts - Directly proportional to mass - Inversely proportional to square of the distance -- Follows an inverse square law F = Gm1/m2/r2

5. Force and Circular Motion (p 260) - Centripetal force - Centrifugal force

6. The Frictional Force (263) - Force opposes motion - Relationship to Centrifugal Force

7. The Gravitational Force at work in our solar system (p263) - Planets -- What about Pluto? (272) - Comets (269) What Causes Gravity (p 274)

8. Brief History of our Solar System (p278)

9. Half-Life: The half-life is the amount of time it takes for half of the atoms in a sample to decay. The halflife for a given isotope is always the same ; it doesn't depend on how many atoms you have or on how long they've been sitting around.always the same For example, the applet will tell you that the halflife of beryllium 11 is 13.81 seconds. Let's say you start with, oh, 16 grams of 11Be. Wait 13.81 seconds, and you'll have 8 grams left; the rest will have decayed to boron 11. Another 13.81 seconds go by, and you're left with 4 grams of 11Be; 13.81 seconds more, and you have 2 grams...you get the idea.

10. This article is about the scientific and mathematical term. For other uses, see Half-life (disambiguation).Half-life (disambiguation) The half-life of a quantity whose value decreases with time is the interval required for the quantity to decay to half of its initial value. The concept originated in the study of radioactive decay which is subject to exponential decay but applies to all phenomena including those which are described by non-exponential decays.radioactive decayexponential decay The term half-life was coined in 1907, but it was always referred to as half-life period. It was not until the early 1950s that the word period was dropped from the name. [1][1] Number of half-lives elapsed Fraction remaining As power of 201/11/2011/21/2121/41/2231/81/2341/161/2451/321/2561/641/267 1/1281/2781/2561/28N1 / 2N1 / 2N

11. The table at right shows the reduction of the quantity in terms of the number of half-lives elapsed Number of half-lives elapsed Fraction remaining As power of 2 01/11/2 0 11/21/2 1 21/41/2 2 31/81/2 3 41/161/2 4 51/321/2 5 61/641/2 6 71/1281/2 7 81/2561/2 8 N1 / 2 N

12. . It can be shown that, for exponential decay, the half-life t1 / 2 obeys this relation: where ln(2) is the natural logarithm of 2 (approximately 0.693), andnatural logarithm λ is the decay constant, a positive constant used to describe the rate of exponential decay.λdecay constantpositive The half-life is related to the mean lifetime τ by the following relation:mean lifetime