push or a pull I A force F

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

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. Siudy 25 N Woods Stolarski exactly the same These two forces are drawn __________ mag. & ______ dir. b/c they have the same _____. exert a force on Woods and Stolarski are said to _____ apply a force to Siudy. We say the forces or ______ act on. Siudy. Sometimes, forces are ______ actions called______.

Fundamental B. ______________ forces: basic • most _______ forces known without • can push or pull _______physical contact. at a distance field • aka “__________” or “ _____ ” forces Earth Ex. Even though ______ is separated from the Moon vacuum _________ by a ______ (nothing), exert forces both objects are able to ___________ on each other. F E F m ¼ million miles

fundamental The 4 _________ forces are listed below from strongest to weakest: strong (nuclear) –force that binds _____ protons 1. _____ nucleus and ______ within the _______ neutrons electromagnetism 2. ___________ (e&m)- the force that acts electric between _______ charges; the source of bonds _______ ; responsible for chemical ____ magnetism molecules atoms or between _________ between _____ weak decay 3. _____ (nuclear)– causes nuclear _____ gravity masses 4. _____ – (Fg) a force between ______ holds planets, solar systems, and galaxies weakest of the 4 here together, but is the _____________ weight aka the _______ (w) of an object when it is on w or Fg planet or near a_______.

Contact C. ________ forces between 2 objects: electromagnetism • result from______________ physical contact • occur when there is _________ Tension 1. __________, T: pull • the _______ of wires, ropes, strings, cables, etc direction • _______ is the direction of the wire, etc length • _______ of wire, rope, etc, not important electron bonding • results from ____________ between within atoms and molecules _____ the wire itself. Ex: ceiling wire weight T tension The ______ is the force exerted by the wire as it pulls up ________on the weight.

Friction 2. _______, Ff : opposes motion (or ______ intended • usually ______ motion) opposite of velocity • direction - usually _______ along the surface • acts ___________ between 2 objects bonds • sliding friction: results as electron ____ between the molecules along the surface break and re-form _____________. v Ex: block sliding along floor to the right. pulls back The surface ________ left to the ____ on the block Ff

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

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

3. The ________ force, FN : normal surfaces • occurs when 2 ________ are in contact perpendicular • direction is _________ ( ) to both surfaces stretch as • results when electron bonds _______ press against surfaces ____________ each other Ex: standing on floor FN pushes The floor _____ the person on ________. Ex: block at rest on an incline FN pushes The incline _____ the block on ________.

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

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

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 FN w Ex 3: block hanging from a wire: ceiling T w

Ex 4: block pulled to left on frictionless table by a pull P Ex 5: block on table sliding to the left, no pull, but with friction P FN P w FN v w not drawn Notice: v is ________ ! Ex 6: block on floor being pulled to left by a rope but not moving rop e Ff T FN w Ff

E. Forces can be added like any other vectors: Add: head to tail: F 1 and: F F 2 parallelogram: F q F 1 Magnitude of resultant force: F = √(F 12 + F 22) Direction of resultant force: q = tan-1(F 2/F 1) F 2

Ex: The resultant of two forces, 3 N and 4 N as a function of q between them: q ( 0) Magnitude of resultant F: Resultant F 0 7 N F 90 5 N 180 F 1 N add Biggest possible magnitude _____ the magnitudes subtractthe magnitudes Smallest possible magnitude _____ As q increases, the magnitude ________ decreases.

resolved F. Forces can be ________ (broken down into ___________ )like any other vectors: x and y components F Fy q Fx Phys. RT: (Mechanics section) Fy = F sinq Fx = F cosq

Ex: Find the x and y components of the F below: 120 N Fy 300 Fx Fy = = F sinq 120 N sin 300 120 (0. 500) 60 N Fx = = F cosq 120 N cos 300 120 (0. 866) 104 N