1. Lecture: Forces, Motion, Gravity and Friction http://www.youtube.com/watch?v=YyJSlcIb d-s

2. What is the metric unit for mass? What is the English unit for Mass (watch it, it’s slimy)? What is the English unit for weight? What is the metric unit for weight? How does weight relate to a force?

3. Variable:English:Metric: MassslugGram (g) WeightpoundNewton (N) (Newton is a force) (F= Mass x Accel) (1N= 1kg x 1m/s 2) the Newton is a measure of two things: 1. weight 2. force THEY ARE THE SAME THING: (YOUR NAMES?) But, this also means weight is a different measure than mass

4. 1. Force: can only occur as two types: A. pull or B. push C. all forces transfer energy to an object, whether it moves or not: wall? D. motion can only be caused by an applied force (w/ direction and magnitude), thus force is a vector E. the amount of force needed to move an object depends on: 1) the mass of the object (prius vs hummer?) and 2) the amount of friction applied to the object resisting motion(ie: smooth vs. rough floor?)

5. F. The metric unit for force is the Newton (N): the amount of force to cause 1kilogram to accelerate at 1 meter per second squared: -the same force a mouse applies to a table top due the gravity acting on its mass; -also = cube of butter in your hand G.force formula: 1N = 1kg x 1m (note: mass in kg) s 2 (measured with a Newton spring scale: ?) H. forces always come in pairs: applied force (draw box w/ pairs?) and the object’s resistant force I. Mass is a measure of the amount of matter (atoms: # amu, see periodic table)

6. J. Weight (not mass!!) a measure (in Newtons of force) of the mass of the object and the amount of acceleration acting on the object: 1. so, what two variables affect weight (force)? weight (force in N) = mass(kg) x acceleration F = M x A (Newton’s 2nd law of motion) 2. so, how much does 1kg of mass weigh on Earth? a. weight = 1kg x 9.8 m/s 2 so it is 9.8N, because the acceleration of gravity on Earth is, for all objects, 9.8m/s 2 (spring scale) and weight is always in units of Newtons b. if we were on the moon, would we weigh six times less or six times more? c. are people on the moon really weightless?

7. K. Show your work: (k, ?k, F, cu, ca, sf): A 50.0 kg mouse runs w/ an acceleration of 2.30 m/s 2, what force is it running at? A 1.2 g humming bird is caught in a birding net w/ an applied force of 0.07 N. What was the bird’s acceleration at the time of capture? L. Forces video #2: http://www.youtube.com/watch?v=MztWyY9z1j Y http://www.youtube.com/watch?v=MztWyY9z1j Y

8. 2. There are four universal forces: A. gravity force 1. always a pull force 2. the size of this force depends on two aspects: a. the mass of the object: thus everything with mass creates its own gravity and the more massive the object, the greater its gravitational field: moon vs Earth vs Sun: this is what keeps planets in orbit, otherwise they fly off into space you vs your neighbor?

9. b. the distance from another object: the greater the distance = less effect of its gravitational force The sun is a more massive object, but what object in our skies effects our tides and why? c. so: increase mass = increase g force (direct relationship) increase distance = decrease g force (indirect relationship)

10. B. electromagnetic force 1. when electricity flows, it creates a magnetic field. Thus, there are two types of forces created which are related: a. electric -between opposite charged particles: balloon -holds atoms together: protons/electrons -stronger than gravity: why the ceiling does not fall down b. magnetic force field -can attract or repel (push or pull): magnets? -magnetic levitation trains?

11. C. strong nuclear force 1. protons and neutrons are made of quarks those quarks are each individually held together by a strong force 2. occurs only over very short distances, w/ non contact 3. break the strong force: produce a nuclear explosion with electricity release D. weak nuclear force 1. holds particles (p & n) within the nucleus together w/non-contact: weak force 2. weak force decay causes neutrons to change (“flavor”) into protons 3. loss of weak force causes the nucleus to decay, releasing radioactivity (beta decay)

12. 3. Friction A. a force opposing motion B. when surfaces move past each other they create this force, of which there are three types: 1. sliding friction: greatest frictional force a. objects slide past one another: feet sliding, tires screeching to a stop b. weight of object effects its amount: greater = more friction rubbing hands together? c. surface types effect its amount: rough vs smooth?

13. 2. rolling friction a. object rolling over another -bowling ball -tires rolling on street -ball bearings 3. fluid friction: least frictional force a. fluid is any object which flows b. ie: gases (wind), liquids (water) c. lubricants change sliding friction to fluid friction: reduces friction C. friction is not always bad: need it to walk, drive: start/stop D. terminal velocity: due to the friction acting on the object such that it is still moving but is slowed by the friction so that it is not accelerating = 0 m/s 2 thus reached it maximum (terminal) velocity

14. 4. Forces and equilibrium things begin moving only if the forces acting on them are unequal. A. balanced forces are when all the forces acting on an object equal zero; thus, there is no speeding up or down in that direction: it is a constant motion (including stopped) for the airplane, which forces are balanced? is it moving in that direction? which forces are unbalanced? is it moving in that direction?

15. B. when the net force is zero the object is in equilibrium: the object is either: not moving: or moving at a constant speed

16. if the net force is not zero (unbalanced), the object is accelerating: positive = going faster negative = going slower

17. if the net force is not zero (unbalanced), the object is accelerating: positive = going faster negative = going slower

18. C. Normal force: an object resting on a surface is applying a downward force on the surface it is resting upon. Because the object does not sink into the surface there is a force pushing it upward. This upward force is the Normal force. It occurs opposite to the direction pushing into the surface.

19. D. free-body diagram a single object only with all forces acting are drawn on the object up forces are positive down forces are negative