1. I. A force, F, is a ____________________________. A. Forces are ______________. magnitude – how ___________________ direction –_________ shows dir. of push/pull Ex 1: F = mag. dir. 20 N SI force units__________________ (derived) 1 N = 1 N ≈ weight of 1______________________ fundamental Ex 2: w = mag. dir. 10 N push or a pull vectors strong or weak newtons, N stick of butter/small apple arrow 20 N, east 10 N (down) 1 kg m/s 2 Sketch:

2. Ex. Woods pushes Siudy with a 25 N force to the right. Stolarski pulls Siudy with a 25 N force to the right. Draw and label both forces using a scale of 1 cm = 5 N. These two forces are drawn ____________________ b/c they have the same __________ & ___________. Woods and Stolarski are said to __________ a force on or ____________ a force to Siudy. We say the forces ____________ Siudy. Sometimes, forces are called____________. Siudy exactly the same mag. dir. Woods Stolarski exert apply act on actions 25 N

3. B. ____________________________ forces: most _____________ forces known can push or pull ______________physical contact. aka “___________________” or “ __________ ” forces basic without at a distance field Fundamental Ex. Even though ___________ is separated from __________________ by a ____________ (nothing), both objects are able to _____________________ on each other. vacuum E m Earth the Moon exert forces F F ¼ million miles

4. The 4 __________________ forces are listed below from strongest to weakest: 1._________ (nuclear) –force that binds __________ and ____________ within the ______________ 2._____________________ (e&m)- the force that acts between _____________ charges; the source of ______________ ; responsible for chemical ________ between _________ or between __________________ 3. _________ (nuclear )– causes nuclear __________ 4.__________ – (F g ) a force between ____________  holds planets, solar systems, and galaxies together, but is the __________________________  aka the _____________ (w) of an object when it is on or near a_____________. strong e lectro m agnetism weak decay electric magnetism bonds atoms molecules gravity masses protons neutrons nucleus weakest of the 4 here planet weight fundamental w or F g

5. C. ________________ forces between 2 objects: result from___________________________ occur when there is _________________ 1.___________________, T: the _______ of wires, ropes, strings, cables, etc _____________ is the direction of the wire, etc ______________ of wire, rope, etc, not important results from ________________________ between atoms and molecules __________ the wire itself. weight wire T The ___________ is the force exerted by the wire as it _______________on the weight. Ex: ceiling electromagnetism physical contact Tension pull electron bonding length Contact direction tension within pulls up

6. 2. ______________, F f : usually ____________ motion (or ____________ motion) direction - usually _____________ of velocity acts _____________________ between 2 objects sliding friction: results as electron ________ between the molecules along the surface __________________________. opposes intended opposite along the surface bonds break and re-form Ex: block sliding along floor to the right. block v FfFf Friction The surface _______________ to the ________ on the block. pulls back left

7. FfFf v = 0 Ex: block at rest on an incline Ex: block being pulled up an incline (ramp) ____________ friction, the block would slide down. This would be its "_______________ " motion. Friction ____________ that motion from happening, so friction must be directed ____________________. v FfFf Without intended up the incline prevents

8. Ex: block accelerated by pulling surface under it: Sometimes friction actually is in the__________ direction as motion. same With respect to the surface, the block's intended motion is to the _______. So the friction must be to the ____________. Instead of _____________ motion, in this case friction ___________ motion: The block _________________ to the right. pull here… block remains at rest surface block left right opposing causes accelerates No friction : Friction : block is pulled along

9. 3. The ________________ force, F N : occurs when 2 ________________ are in contact direction is _________________ ( ) to both surfaces results when electron bonds _____________ as surfaces _______________________ each other Ex: standing on floor Ex: block at rest on an incline FNFN FNFN normal surfaces perpendicular stretch The floor _________ on _______________. pushes The incline _________ on _______________. pushes the personthe block press against

10. D. Usually __________________ force acts on an object at a time. ________________ diagrams make it easier to solve these problems. more than 1 "Free body" point Rules for drawing free-body diagrams: 1. Imagine a _____________ surrounding the object. 2. List all: a/ "______________" forces that cut through it b/ "_________________" forces that cut through it 3. Draw a _______________ to represent the object. 4. Draw each force in step 2 as an ___________ whose tail begins at that _____________. 5. Only draw _____. Do NOT draw _____________ ! surface contact at a distance arrow point F's v's, d's, etc

11. Drawing or sketch of object with many forces acting on it: Free body diagram (FBD) of same object: w T FNFN FfFf hill rope Ex: Mr. Siudy holds himself on a hillside by pulling on a rope.

12. Draw a FBD of the forces acting on the blocks in each case below. Ex 1: block in free fall (no air resistance) w Ex 2: block on table at rest w FNFN Ex 3: block hanging from a wire: w T ceiling

13. Ex 4: block pulled to left on frictionless table by a pull P Ex 6: block on floor being pulled to left by a rope but not moving w w FNFN FNFN P P T FfFf Ex 5: block on table sliding to the left, no pull, but with friction w FNFN v FfFf Notice: v is _______________ ! not drawn rope

14. E. Forces can be added like any other vectors: head to tail: parallel- ogram: Add: and: F F F1F1 F2F2 F1F1 F2F2 F1F1 F2F2 Magnitude of resultant force: F = Direction of resultant force:  = √ (F 1 2 + F 2 2 ) tan -1 (F 2 /F 1 )  

15. Ex: The resultant of two forces, 3 N and 4 N as a function of  between them:  ( 0 ) Resultant Magnitude of resultant F: 0 90 180 Biggest possible magnitude  __________ the magnitudes Smallest possible magnitude  __________ the magnitudes As  increases, the magnitude ________________. 7 N 5 N 1 N add subtract decreases F F F

16. F. Forces can be _______________ (broken down into _____________________ )like any other vectors: F F y =  resolved x and y components F sin  FxFx FyFy F cos  PhysRT: (Mechanics section) F x =

17. Ex: Find the x and y components of the F below: F cos  = 120 N cos30 0 = 120 (0.866) = 104 N 120 N   F sin  = 120N sin30 0 = 120 (0.500) = 60 N F y = F x = FxFx FyFy