1. 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______________________

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

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

13. 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

14. √(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)

15. 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

16. 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

17. 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

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

21. 270
34 N
13 N
510
2/ 1 cm:2N
1/ 1 cm:5N

22. 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