I. A force, F, is a ____________________________. A. Forces are ______________. magnitude – how ___________________ direction –_________ shows dir. of.

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

vectorsstrong or weak

newtons, N

stick of butter/small apple

arrow

20 N, east 10 N (down)

1 kg m/s2

Sketch:

Ex. Woods pushes Siudy with a 25 N force to theright. 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 samemag. dir.

Woods Stolarski

exertapply

act on

actions

25 N 25 N

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

The 4 __________________ forces are listed belowfrom 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.__________ – (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

electromagnetism

weak decay

electricmagnetism bonds

atoms molecules

gravity masses

protonsneutrons nucleus

weakest of the 4 here

planet

weight

fundamental

w or Fg

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

TThe ___________ is the forceexerted by the wire as it_______________on the weight.

Ex: ceiling

electromagnetismphysical contact

Tension

pull

electron bonding

length

Contact

direction

tension

within

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

__________________________ .

opposes intended

opposite

along the surface

bonds

break and re-form

Ex: block slidingalong floor to theright.

block

v

Ff

Friction

The surface _______________to the ________ on the block.

pulls backleft

Ffv = 0Ex: 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

Ff

Withoutintended

up the inclineprevents

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 intendedmotion 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

surfaceblock

leftright opposing

causesaccelerates

No friction:

Friction: block is pulled along

3. The ________________ force, FN :

• 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 inclineFN

FN

normal

surfacesperpendicular

stretch

The floor _________on _______________.

pushes The incline _________on _______________.

pushesthe person the block

press against

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

contactat a distance

arrow

point

F's v's, d's , etc

Drawing or sketch of object with many forces acting on it:

Free body diagram (FBD) of same object:

w

TFN

Ff

hill

rope

Ex: Mr. Siudy holds himself on a hillsideby pulling on a rope.

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

FN

Ex 3: block hangingfrom a wire:

w

Tceiling

Ex 4: block pulled to left on frictionlesstable by a pull P

Ex 6: block on floor being pulled to left bya rope but not moving

w

w

FN

FN

P P

TFf

Ex 5: block on table sliding to the left, nopull, but with friction

w

FNv Ff

Notice: v is _______________ !not drawn

rope

E. Forces can be added like any other vectors:

head to tail:

parallel-ogram:

Add: and:

F F

F1 F2

F1

F2

F1

F2

Magnitude of resultant force: F =

Direction of resultant force: =

√(F12 + F2

2)

tan-1(F2/F1)

Ex: The resultant of two forces, 3 N and 4 N as a function of between them:

(0) ResultantMagnitude 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

addsubtract

decreases

F

F

F

F. Forces can be _______________ (broken downinto _____________________ )like any other vectors:

F

Fy =

resolvedx and y components

F sin

Fx

Fy

F cos

PhysRT:(Mechanics

section) Fx =

Ex: Find the x and y components of the F below:

F cos = 120 N cos300

= 120 (0.866) = 104 N

120 N

F sin = 120N sin300

= 120 (0.500) = 60 N

Fy = Fx =

Fx

Fy