push or a pull I. A force, F, is a ____________________________ . vectors A. Forces are ______________ . magnitude – how ___________________ direction –_________ shows dir. of push/pull strong or weak arrow Ex 1: F = 20 N, east Ex 2: w = 10 N (down) mag. mag. dir. dir. 10 N Sketch: 20 N newtons, N SI force units__________________ (derived) 1 N = 1 kg m/s2 fundamental stick of butter/small apple 1 N ≈ weight of 1______________________

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

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

fundamental The 4 __________________ forces are listed below from strongest to weakest: _________ (nuclear) –force that binds __________ and ____________ within the ______________ _____________________ (e&m)- the force that acts between _____________ charges; the source of ______________ ; responsible for chemical ________ between _________ or between __________________ _________ (nuclear)– causes nuclear __________ 4.__________ – (Fg) 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 protons neutrons nucleus electromagnetism electric bonds magnetism atoms molecules weak decay gravity masses weakest of the 4 here weight w or Fg planet

C. ________________ forces between 2 objects: Contact C. ________________ forces between 2 objects: result from___________________________ occur when there is _________________ electromagnetism physical contact ___________________, 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. Tension pull direction length electron bonding within Ex: ceiling wire tension The ___________ is the force exerted by the wire as it _______________on the weight. T weight pulls up

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

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

Extra slide: Sometimes friction actually is in the__________ direction as motion. same Ex: block accelerated by pulling surface under it: block pull here… surface block remains at rest No friction: Friction: block is pulled along 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. left opposing right causes accelerates

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

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

Ex: A student holds herself on a hillside by pulling on a rope. Drawing or sketch of object with many forces acting on it: Free body diagram (FBD) of same object: T rope FN 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 ceiling Ex 3: block hanging from a wire: T w

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

√(F12 + F22) E. Forces can be added like any other vectors: Add: F1 and: F2 head to tail: parallel- ogram: F F F2 F2 q q F1 F1 Magnitude of resultant force: F = Direction of resultant force: q = √(F12 + F22) tan-1(F2/F1)

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

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

Ex: Find the x and y components of the F below: Fy 300 Fx Fy = F sinq = 120N sin300 = 120 (0.500) = 60 N Fx = F cosq = 120 N cos300 = 120 (0.866) = 104 N

Open your 3-ring binder to the Worksheet Table of Contents. Record the title of the worksheet: Sum of All Forces WS

270 34 N 13 N 510 2/ 1 cm:2N 1/ 1 cm:5N

1 cm:10 N 42N 1 cm:4 N 10 N 200 460 6.5 cm  26N 4.2 cm  42N 1 cm:3 N 1 cm:8 N Fx = 0 Fx = 40 N Fy = 0 Fy = -6 N