Mental note for next year.

1
Mental note for next year. Do Hookes law here
with forces (or later with energy)
2
If an object is stationary, what will cause it
to start to move
A FORCE
3
But what is a force??
A force is a push or a pull on something by
something
Does a push have a direction?
FORCES ARE VECTORS, Magnitude and Direction
4
The force on the truck is a push by the man
Since the truck increased its speed we say that
it has..
Accelerated
5
Forces cause objects to accelerate in the
direction the force is applied.
6
What are the 3 ways an object can accelerate?
7
What is the direction of the force?
The car accelerates to the right (X)
8
Which way would you apply a force to cause the
truck to slow down?
The car accelerates to the left (-X) while slowing
9
In what direction should a force be applied in
order for the truck to make a right turn?
10
What if two people push equally hard on both
sides of the truck. In what direction will it
accelerate?
FORCES ARE BALANCED IF THEY ARE EQUAL AND
OPPOSITE.
But EQUAL what? and OPPOSITE what?
Equal Magnitude but Opposite Direction
11
What if two people push equally hard on both
sides of the truck. In what direction will it
accelerate?
FORCES ARE BALANCED IF THEY ARE EQUAL AND
OPPOSITE.
But EQUAL what? and OPPOSITE what?
Equal Magnitude but Opposite Direction
12
Forces are vectors if each what would you get if
you added to two vectors.
13
Balanced Forces cancel out in both magnitude and
direction
Consider the Forces acting on the balls below
balanced
NOT
balanced
NOT
balanced
balanced
14
If you shove a book across a table your
hand accelerates it. After it leaves your hand
what will happen to the books speed.
WHY does it slow down?
Friction
15
Galileo experimented with Spheres on a level
surface and found that they slowed very little.
Because they have very little friction
16
Galileo concluded if there was absolutely no
friction the ball would
JUST KEEP ROLLING AND NEVER STOP (Or even slow
down)
17
This is opposite what everyone thought (at the
time)
An objects natural state is at rest!
This was common sense regarding objects around
them. (planets had their own natural states)
18
Sir Isaac Newton studied how objects move too.
Developed calculus About the age of 20 in order
to describe motion
19
He lays the foundation for modern physics in his
book Principia when he was 24. The physics we
are learning now is called Newtonian Physics
which is modified by Einstein later. Newtonian
Physics is an approximation which works GREAT
unless you are dealing with EXTREME
circumstances. (moving close to the speed of
light etc)
20
In Newtons 1st of 3 laws of motion he restates
Galileo NEWTONs 1st LAW An object will move
at a constant velocity unless an unbalanced force
acts upon it
A force not cancelled out by another one
21
Which ball has a constant velocity?
Which ball has balanced forces?
Newtons first law is often stated as An object
at rest tends to stay at rest and an object in
motion tends to stay in motion UNLESS an
unbalanced force acts on the object.
22
If an object is stationary or moving in a
straight line at a constant speed its velocity is
constant. Forces must be balanced.
23
Two ping pong balls are launched into space and
experience no wind resistance or any other
forces. The first is launched at 25 m/s and the
other at 3 m/s. Which will come to a stop FIRST?
NEITHER--- THEY WILL BOTH KEEP MOVING FOREVER
24
Soccer ball hover disk demo
25
INERTIA the property of matter that resists
changing velocity. It is the laziness of matter
to just keep doing what it was doing.
26
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27
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28
Which way will tighten the hammer head to the
shaft.
29
Why isnt the top of the card flying forward?
30
If you are driving too fast and hit a tree head
on, What force would send you through the
windshield if you werent wearing your seat belt?
Crash Test - No seat belt
Crash Test - With seat belt
31
When people are hit from behind, sometimes they
experience whiplash. What is it and what causes
it?
32
You put your cell phone down in the seat next to
you while driving 60 mph. What happens?
33
What keeps a ball in motion after it is thrown?
Is inertia a force?
Does air exert a force? Does wind resistance
speed up or slow down a projectile?
34
A tennis ball has inertia, and you would have to
exert a force on it to slow it down from 25 mph
to a stop.
35
An 18 wheeler also has inertia, would you want to
slow it down from 25 mph?
36
HOW MUCH INERTIA an object has depends on its
Mass. The more mass an object has, the harder it
is to change its velocity. More massive objects
are lazier to speed up, slow down, or change
direction. INERTIA is NOT a force.
37
BOWLING BALL GRAND PRIX
38
Notation for Forces
The object of interest being pushed or pulled
F
Type, Feeler, Dealer
The thing doing the pushing or pulling
39
Fg
Gravity
Types of Forces
Fg
Always down or toward the center of the earth
Depends on the mass of an object
Fg, diver, earth
40
Normal
FN
Types of Forces
A push resulting from two objects contacting
Always perpendicular to the surface and away from
it
FN, elephant, pedestal
41
The normal force is always perpendicular to the
surface
42
What is the direction of the normal force on the
marble?
43
Is the elephant accelerating?
No, then all forces cancel. What is cancelling
out FN?
FN
44
If Forces do not cancel, then whats leftover is
called the NET force
F1
F2
20.00 made 15.00 spent 5.00 NET
(whats leftover)
45
If Forces do not cancel, then whats leftover is
called the NET force
F1
5 N
F2
-9 N
Realize that to find the Net force you have added
the two vectors and found the .....
46
IF forces DO cancel (balance) then FNET
F1
SF or FNET 0
9 N
F2
9 N
If SF 0, what is the motion like for the object
47
A Find the net force on each object
10 N
10 N
15 N
10 N
48
Tension
Types of Forces
FT
FT
Always a pull in the direction of the cable
FT, block, string
49
What is the direction of the tension force on her
hands?
50
Friction
Types of Forces
FF
FF
Contact Force
opposite direction of motion (or impending motion)
FF, player, dirt
51
A crate sits motionless on a hill, Which
direction is the FF acting?
52
What happens to the following rolling balls when
a force is applied, The direction of the movement
of the ball is shown on the ball in blue.
Slow down
Speed UP
Change Direction
53
What happens to the following rolling balls when
a force is applied, The direction of the movement
of the ball is shown on the ball in blue.
Slow down
Speed UP
Change Direction
54
What will happen to the ball at rest, when
balanced forces are applied?
Force
Force
still
IT REMAINS STILL
55
What will happen to the moving ball, when
balanced forces are applied?
It keeps moving at the same speed in a straight
line.
56
A Freebody diagram replaces the object of
interest with a dot (to simplify the scenario)
57
Then forces acting on the object are represented
by arrows (vectors) extending out from the dot in
the proper direction. It doesnt matter where
the forces act on the boy just the direction of
the force.
FN,boy,pillow
Fg,boy,earth
58
If the object doesnt accelerate then forces must
balance (SF0)
FN,boy,pillow
Fg,boy,earth
59
Draw a free body diagram for a motionless
wrecking ball.
Are the forces balanced?
SF0
60
What would be different if the ball was moving
upward at a constant speed?
Are the forces balanced?
SF0
FT,ball,cable
Fg,ball,earth
61
What would be different if the ball was moving
downward at a constant speed?
Are the forces balanced?
SF0
FT,ball,cable
Fg,ball,earth
62
What would be different if the ball was moving
upward faster and faster?
Are the forces balanced?
63
Force diagram practice sheet in class
64
Wind resistance
A force exerted by air which is opposite the
direction of motion. (like friction)
Does the magnitude of the force change based on
how fast an object is moving. (Think about
driving with your hand out the window)
65
Terminal Velocity
When a sky diver First jumps out of a plane they
are falling slowly so the force of air resistance
is low (at least upward)
Fg, diver, earth
66
Falling slowly
Falling Fast
FF, diver, air
Fg, diver, earth
FNET 0
Is there a net force?
When the forces are equal does the diver stop
falling?
67
The diver is falling fast and must slow down,
what does he do?
Opens a parachute (how will forces change)
FNET 0
Does he start going UPWARDS???
68
Equal weights on pulley demo
69
Bungee jumping when he first jumps off what
forces are acting on him (lets ignore wind
resistance on this one)
70
When the slack is out of the cord it starts to
pull but very weakly. Net FORCE? What happens
to the jumper?
FT, jumper, cord
Fg, jumper, earth
71
As the cord stretches it pulls harder Net FORCE?
What happens to the jumper?
FT, jumper, cord
Fg, jumper, earth
72
Eventually it is pulling equally hard as
gravity Net FORCE? What happens to the jumper?
FT, jumper, cord
Fg, jumper, earth
73
The jumper keeps falling and stretching the cord
further. Net FORCE? What happens to the
jumper?
FT, jumper, cord
Fg, jumper, earth
74
free body diagrams WS 2
75
Hovercraft analysis WS
76
SF 0
In order for the
then
Forces Up Forces Down
Forces Left Forces Right
77
In what direction would the object below
accelerate?
SF 0
78
In what direction would the object below
accelerate?
SF 0
79
In what direction would the object below
accelerate?
SF 0
80
In what direction would the object below
accelerate?
81
Create a free-body diagram for the ball player
who is sliding (and slowing) into 2nd base.
Are the forces balanced?
We have left a few forces out of the picture,
lets fill them in now.
Which forces cancel?
Can friction cancel any of the other two forces?
82
Make free body diagrams for the hover puck that
is off and stationary
being slowed by a push
being pushed
coasting
on and stationary
83
Make a free-body diagram for the person who is
not moving
84
Forces that act at an angle can be thought of as
made up of an X component and a Y component.
F
85
For example if the object below is not
accelerating with 3 forces acting on it then....
C
A
B
86
If the force of gravity on each weight is 50
N. What is the tension in each cable?
87
SF0
Make a freebody diagram For the stationary ring
88
Make a freebody diagram for the ring supported by
a rod and cable. If the everything is stationary.
cable
rod
89
Make a free body diagram for the basketball,
Are the forces balanced?
F g, ball, earth
90
Create a free-body diagram for a cannonball,
moving at a constant 2,000 m/s through empty
space.
91
Draw a freebody diagram for the pendulum below.
92
Create a freebody diagram for the crate which is
pulled by a rope at a constant speed along level
ground
93
Draw a freebody diagram for a box which is
stationary on a ramp.
Is there a Net Force?
SF 0, Whats Missing?
FN
Fg
q
94
Turn the whole page so that it looks flat Break
gravity into its components
95
The object is at equilibrium so.
FUP FDown
FN
FLeft FRight
FF
Fg
96
Draw a freebody diagram for a box sliding down a
frictionless ramp
Will it accelerate?
Which way?
What is the direction of the net force?
97
A trick is to rotate the page until the slope is
flat
98
Use your turned page to define up/down left
right.
Now break gravity into its two components.
Consider the direction of acceleration, Which
forces must cancel?
FN
What is the Fnet
99
Freebody diagram WS 2
Gravity and page tilting
100
Mass Weight
101
What is matter?
I will summarize this at the end so dont take
notes on all this
MATTER -
anything that has mass and volume
Is everything matter?
102
What is matter and what is not?
Car
1 liter of nothing (a vacuum)
thought
Earth
feeling
water
air
light bulb
?
light
103
Volume
how much space an object takes up
104
Mass indicates how much matter is in an
object
On earth the more mass an object has the more it
weighs.
The more mass an object has the harder it is to
get moving or stop moving.(inertia)
105
Weight The force of gravity on an object
106
If you go into space, there is no gravity. So
you have no weight.
Did you lose any matter?
You still have the same mass but no weight.
107
Kicking cans 1 empty 1 filled with
sand 1 filled with lead.
The more mass an object has the more inertia it
has And the harder it is to get going.
108
If you and a huge fully loaded dump truck took a
trip to space
Could you grab it and shake it up and down easily?
109
Mass is measured in grams or kilograms
or slugs
Weight is measured in pounds or newtons
How do we measure mass on earth? With a scale
that basically measures its weight. If you took a
triple beam balance into space, even though it
says it measures mass it really measure weight.
110
SUMMARY write this down
Mass how much matter is in an object how
much inertia an object has How lazy an
object is to change what it is
doing Units of Kilograms
Weight the force of gravity on an object Units
of Newtons (N)
111
(weight)
Fg m g
Mass (kg)
9.8 m/s2 (on earth)
What is the force of gravity on 1 kg object (on
earth)
112
The force of gravity (weight) on a 1 kg object is
9.8 N
kg m
1 N
1
s2
113
An object weighs 250 N on earth, what is its mass?
114
Draw a freebody diagram for a 3 kg book sitting
motionless on a desk. Then give the magnitudes
of all forces.
115
A spring scale can be used to determine the mass
of an object.
Demo with a mass
Does it measure mass or force?
A spring scale measures force (show with
finger) It has a Newton scale also. How can it
tell us the mass of an object?
But the more mass an object has, the more weight
(Force) it has.
116
A spring scale reads 10 N when holding a 10 N
mass. What will 2 scales read when holding up the
same mass?
0 N
10 N
10 N
10 N
117
A girl sitting in a swing has weight of 100
N. What is the tension force in each chain?
118
How strong does the rope need to be in each case
if the person and seat have a mass of 72 kg? Is
it the same?
B
119
If unbalanced forces are applied to an object,
there is always a SINGLE force will cancel out
the other forces. It is called the EQUILIBRANT,
because it establishes equilibrium
What would the equilibrant be in the following
cases
10 N
120
What is the equilibrant in the following cases
with 2 or more forces. The length of the vector
indicates the magnitude of the force
10 N
10 N
121
What is the equilibrant in the case below
10 N
15 N
122
What single force would cancel out these two
forces?
First add them together and find their resultant,
then find the opposite
25 N
10 N
123
Lets try one on the board. What single force
will cancel a 50 N force at 30o N of E and a 25 N
force at 40o S of E?
50 N
30o
40o
25 N
124
Equilibrant WS
125
For an object at equilibrium, all forces must
cancel. So one of the forces must be the
equilibrant for all of the other forces?
A B C 0
B
A
C
126
The resultant of A B is equal and opposite of C
A B - C
B
A
C
127
The resultant of B C is equal and opposite of A
B C -A
B
A
C
128
The resultant of A C is equal and opposite of B
A C -B
B
A
C
129
Equilibrant WS
130
A 120 N girls sits in a swing The FT in each
chain is 60 N
60 N
60 N
120 N
131
If the chains are slanted out at 30o, will the
force in each go Up, down, or stay the same
?
?
Consider an example with 2 spring scales and a
mass
120 N
132
If the chains are slanted out, will the force in
each chain go Up, down, or stay the same
?
?
Draw a free body diagram
120 N
133
The length of the cable does not tell us its
force, just the direction of the force. To
find how much we need to draw to scale
30o
120 N
Fg 120 N
134
The two tension forces must cancel out the force
of gravity which means, that their resultant is..
30o
120 N
Fg 120 N
135
Now to finish off the parallelogram, but how?? I
only know the directions of the forces?
30o
120 N
Fg 120 N
136
Now draw the tension vectors
30o
120 N
Fg 120 N
How would we find the number of Newtons of
tension?
In this case the tension in EACH rope is 120 N.
137
Why is the tension in the cable twice what it
would be if they were both straight up?
FT1 120 N
FT2 120 N
30o
120 N
Fg 120 N
138
Just to connect with to what we have done before
in free body diagrams. What do we know about the
component vectors?
FT1
FT2
30o
120 N
Fg
139
Just to show you with all of the numbers
120
120
60 N
60 N
30o
104 N
104 N
120 N
120 N
Much of the tension in the rope just cancels
horizontally
140
120 N
Fg
Which cables will have more tension in them?
120 N
Fg
141
60o
Fg
145 kg
30o
145 kg
Fg
142
60o
Fg
145 kg
30o
145 kg
Fg
143
60o
Fg
30o
FTX
Fg
144
Which rope is more likely to break?
145
Which rope is more likely to break?
146
Two cables both at 40o from the horizontal are
holding up a 15 kg mass. Find the force of
tension in each cable.
147
What if 1 cable is at 45o and the other at 20o.
Is the tension in each the same?
5.0 kg
148
Fg
149
Fg
150
Book problems page 57-58
21, 25, 36
Concept WS
151
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152
Force Mass and Acceleration Lab
153
So if a net force is on an object it
accelerates Is that all there is too this?
What if I blew the yard blower on a tennis
ball, then a bowling ball?
154
IF the SAME Force is applied to different
objects, How quickly they speed up depends on
their
MASS
155
Newtons 2nd law
Force is proportional to mass x acceleration
F m a
NET
Note that Force and acceleration are vectors
An object will accelerate in the direction of NET
force,
156
UNITS???
F m a
m
Kg
s2
Newton
157
Newton
1 Newton of force is equivalent to the weight of
100 mL of water or about 1/5 of a pound.
158

m
F m a
a
F
The Force increases?
What happens to Acceleration if
The Mass increases?
159
If a force of 800 N is applied to a 1200 Kg car,
what is its acceleration?
What force is needed to accelerate a 1300 Kg car
at 2.5 m/s2?
A 3.0 Kg object has a force of 250 N pushing it
forward and 650 N pushing it backwards. What is
it acceleration?
A 3.0 Kg object has a force of 250 N pushing it
forward and 250 N pushing it backwards. What is
it acceleration?
What force would be required to accelerate a 1200
kg car from rest to 15 m/s in 6 seconds?
160
A 1 kg mass and a 10 kg mass are dropped which
hits the ground first?
BUT WHY?????
161
Does the larger mass have a bigger Force (of
gravity) accelerating it ???
force
1
force
10
YES 10 x as much
162
But the larger mass also has more inertia!!!!
a
force

1
mass
The 10 kg has 10 x as much Force on it and 10
times as much inertia
force
10

a
mass
163
If the same force is applied to a 1 kg mass and
a 2 kg mass. Compare their accelerations
Compared to the 2 kg object, After 2 seconds
will the 1 kg object have gone the same
distance twice as far ½ as far 4 times as
far?
164
A truck can accelerate at 5 m/s2 fully loaded. At
what rate can it accelerate after it drops off
its load And decreases its mass to ¼ of its
original mass?
165
Two forces are applied to boats, What is the
acceleration?
166
NET FORCE determines acceleration!!!!!!
167
A rope pulls on a 5 kg bucket with a a force of
120 N. What is the buckets acceleration? Dont
forget about gravity here.
How much force would need to be applied to move
it upward At a constant 2.5 m/s?
168
F ma WS
169
One student sits down in a wheeled chair. And
another student stands and pushes them.
Two students on wheeled chairs push off of each
other
Two students on wheeled chairs, one student
pushes the other
170
What force accelerates the car forward
FF tire, road
171
The answer can be found by simply jumping off an
untethered boat.
In order for you to make it to the dock the boat
must exert a force on you
FN, person, boat
172
The boat pushes you forward but.
You exert a force on the boat which is Equal in
magnitude Opposite in Direction
FN, boat, person
FN, person, boat
173
Forces come in pairs -action reaction
pairs For every action there is an equal and
opposite reaction (force)

174
Newtons 3rd Law
Or restated
Whenever two objects are in contact they exert
equal and opposite forces on each other called
action reaction.
this is NOT a conscious push or pull, it is an
inescapable law of nature.
175
Newtons 3rd Law
Reminder- the equal and opposite forces are on
DIFFERENT objects.
176
Activity Pair up and everyone take a spring
scale. Hook the ends together and
have 1 person pull with a force of 4 newtons and
the other with a force of 8 N
177
While the ball is in contact with the face There
is a force on the player
HOW DO WE KNOW THIS?
178
While the ball is in contact with the face There
is a force on the player AND ON THE BALL
HOW DO WE KNOW THIS?
179
These forces are equal and opposite
They are on different objects.
This is not a conscious push.
FN,Ball,Person
FN, Person, Ball
180
These forces are equal and opposite
They are on different objects.
Do the forces cancel each other out?
FN,Ball,Person
FN, Person, Ball
No, they are on different objects.
181
Action Reaction forces dont cancel each other
because they are on different objects.
5 N
5 N
5 N
5 N
182
Common Sceniarios
Catching a ball Hammering a nail Driving a car A
falling ball
What are the action reaction forces
183
When a gun or cannon is fired, what are the
action reaction pair?
Compare the forces each object feels
They will both accelerate, do they both speed up
the same?
184
Your jet pack stops working you are drifting
away. All you have is a hammer. What do you do?
185
What makes the shuttle go?
186
Think back to firing a gun. What are the action
reaction forces.
187
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188
Fuel
Oxygen
What is direction of the net force on the exhaust
What is the reaction force?
189
FORCES ON AN AIRPLANE
190
How does an airplane wing generate lift?
191
CONSIDER A WING MOVING THROUGH THE AIR
What direction is the force applied to the air
molecule, think about making El Nino perform a
sharp turn
192
Wings are usually at shallow angles
F N,wing, air
lift
F N,wing, air
lift
drag
drag
193
A person is stationary on a floor what is an
action reaction pair of forces?
Are these forces a action reaction pair?
No they are both parts of two interaction pairs
194
What is an action reaction pair for A person
standing on a scale If the force of gravity on
the person is 350 N. What does the scale read? A
car running into a tree
195
A big kid pushes a little kid on frictionless
ice, who feels the bigger force?
196
A little kid and a big kid are holding a rope (on
frictionless ice) If the big kid yanks on the
rope, who feels the greater force?
They both feel the same amount of force!! Again
a consequence of Newtons 3rd law. A rope just
transfers that force.
197
Both objects connected to a rope feel same amount
of force. Think about what happens if one side
lets go.
198
Newtons Third Law Competition
There are 6 questions, work in groups of 4 Write
your answers on a piece of paper with your group
names Dont write on the hand outs. OK The group
that gets the most correct will get 2 BP per
person A tie will result in 1 BP for all members
involved. You have 10 minutes to come up with
your answers. Then we will go over them
199
Book problems Page 84 85 24, 25, 28, 32, 33,
35, 36, 37, 38, 39 due Fri
200
Friction
What would life be like without it?
201
Friction
If an object slows down, where does its Kinetic
Energy go?
What causes it?
202

• all surfaces are rough on a microscopic scale.

203
Frictional force can also be thought of as a lot
of teeny weeny normal forces resulting from
points of contact
204
also may be some attraction between the atoms and
molecules between two surfaces
This is definitely the case when it comes to many
adhesives
205
Two types of Friction

• Force that opposes the motion or impending motion
  of two surfaces in contact

FF,box,ground
206
Kinetic or Sliding Friction- objects are sliding
Static Friction- objects are not sliding
FF,box,ground
207
Friction Lab
208
Friction Lab Recap
Factor
Effect on FF
Weight pushing down
Area of Contact
No Effect
Materials in Contact
Depends on Materials
Static vs Kinetic
Static gt Kinetic
Velocity of Object
No effect
209
DOES depends on

• Types of material in contact (rougher more)

FF

• Greater Normal force more friction

• Whether the object is moving or not
• (static is more than kinetic)

• It does NOT depend on

• the area of contact
• the speed of movement

210
FF mFN
Normal Force in N
Friction Force in N
Coefficient of Friction Fudge Factor based on
Materials in contact Moving (kinetic, mK)
or Stationary (static, mS )
What are the units on m?
211
Why FN not just Fg
(sometimes they are the same) consider a
stationary box
FN
Fg
212
Why FN not just Fg
(sometimes they are different) If another force
is pushing down or up
FN, box, floor
Fg, box, earth
Frocket
213
Why FN not just Fg
(sometimes they are different) If another force
is pushing down or up
FT, box, rope
FN, box, floor
Fg, box, earth
214
Why FN not just Fg
(sometimes they are different) If the surface is
not level
FN, box, floor
Fg, box, earth
215
Some examples of coefficients of friction
ms
mk
.65
.8
rubber/dry concrete
.40
.60
rubber/wet concrete
.58
.78
steel / steel (dry)
.06
.15
steel / steel (oiled)
.4
dry auto brakes
.2
wet auto brakes
Why is it easier to spin your tires when it is
wet?
216
Smooth Surface
Rougher Surface
217
(No Transcript)
218
Block is stationary - STATIC FRICTION
(the harder you pull, the greater Friction
resists)
FF ms FN
FF (N)
Time
219
When the applied force exceeds the maximum
FF, the object slips and begins to move
kinetic friction
FF ms FN
FF (N)
FF mk FN
Time
220
The wheel of a tire is rolling down the road, the
driver hits the gas and friction drives the wheel
forward.
Is this Static Friction or Kinetic
Friction?
221
People have been known to let some air out of
their tires when street drag racing to get more
contact with the road. Does this help
acceleration?
222
What is weight?
What is a situation that makes you feel heavier
or lighter?
223
What does your bathroom scale measure?
Mass or Force
224
Is mass a force?
NO, but it can exert a force, What is causing the
person to exert a force
Fg m g
225
Weight is a force
It changes depending on where you are earth vs.
the moon
the acceleration on object would experience on
the moon is 1.6 m/s2 What force would 65.8 kg
exert there?
F ma 65.8 kg 1.6 m/s 110 N I have lost
84 of my weight!!
226
The FEELING of weight or weightlessness (like
that tickle in your stomach when you go over a
hill) comes from feeling the forces at work you.
Forces on your outside- like your butt in a
chair or feet on the floor Forces on your
inside- your guts being pushed by your pelvic
bone
227
Your apparent weight also depends on if youre
movement
How do you feel when?
The elevator starts upward
Heavier
after you get going
Same
Slowing down to a stop
Lighter
the elevator cord is cut
Weightless
228
FN,you,floor
you feel normal
F net 0
stationary
Fg,you,earth
You feel heavier not because you weigh more but
because the floor is pushing harder on you.
(Your pelvic bone has to push harder on your
insides as well)
229
FN,you,floor
you feel normal
F net 0
stationary
Fg,you,earth
moving up but slowing
You feel lighter not because you weigh more but
because the floor is barely pushing on you. You
get a tickle in your stomach