_Mrs. B._ Very well. This figure (fig. 4. plate 2.) represents a billiard table; now if you draw a line A B from the point where the ball A strikes perpendicular to the cushion, you will find that it will divide the angle which the ball describes into two parts, or two angles; the one will show the obliquity of the direction of the ball in its passage towards the cushion, the other its obliquity in its passage back from the cushion. The first is called _the angle of incidence_, the other _the angle of reflection_; and these angles are always equal, if the bodies are perfectly elastic. _Caroline._ This then is the reason why, when I throw a ball obliquely against the wall, it rebounds in an opposite oblique direction, forming equal angles of incidence and of reflection. _Mrs. B._ Certainly; and you will find that the more obliquely you throw the ball, the more obliquely it will rebound. We must now conclude; but I shall have some further observations to make upon the laws of motion, at our next meeting. Questions 1. (Pg. 32) On what is the science of mechanics founded? 2. (Pg. 32) In what does motion consist? 3. (Pg. 33) What is the consequence of inertia, on a body at rest? 4. (Pg. 33) What do we call that which produces motion? 5. (Pg. 33) Give some examples. 6. (Pg. 33) What may we say of gravity, of cohesion, and of heat, as forces? 7. (Pg. 33) How will a body move, if acted on by a single force? 8. (Pg. 33) What is the reason of this? 9. (Pg. 33) What do we intend by the term velocity, and to what is it proportional? 10. (Pg. 33) Velocity is divided into absolute and relative; what is meant by absolute velocity? 11. (Pg. 33) How is relative velocity distinguished? 12. (Pg. 34) How do we measure the velocity of a body? 13. (Pg. 34) The time? 14. (Pg. 34) The space? 15. (Pg. 34) What is uniform motion? and give an example. 16. (Pg. 34) How is uniform motion produced? 17. (Pg. 34) A ball struck by a bat gradually loses its motion; what causes produce this effect? 18. (Pg. 35) If gravity did not draw a projected body towards the earth, and the resistance of the air were removed, what would be the consequence? 19. (Pg. 35) In this case would not a great degree of force be required to produce a continued motion? 20. (Pg. 35) What is retarded motion? 21. (Pg. 35) Give some examples. 22. (Pg. 36) What is accelerated motion? 23. (Pg. 36) Give an example. 24. (Pg. 36) Explain the mode in which gravity operates in producing this effect. 25. (Pg. 37) What number of feet will a heavy body descend in the first second of its fall, and at what rate will its velocity increase? 26. (Pg. 37) What is the difference in the time of the ascent and descent, of a stone, or other body thrown upwards? 27. (Pg. 37) By what reasoning is it proved that there is no difference? 28. (Pg. 38) What is meant by the momentum of a body? 29. (Pg. 38) How do we ascertain the momentum?