Download Dynamics

Force and the resulting motion
Unification Theory)
Push or Pull
Influence
Contact
No contact
The push or pull is
delivered through
contact.
The influence is delivered
through space without
contact.
Examples are kick, tug,
punch, heave, friction,
buoyant force, etc.
Examples are magnetic,
electric, gravity, etc.
Push/Pull
Friction
Friction
Gravity
Electroma
gnetic
Magnetic
Electric
Gravity

Electromagnetic force results from the interactions
defined by law of poles and law of charges, in the
basic level.
 Involves the concept that a proton attracts an electron; an
electron repels another electron.

Gravitational force is present between matter as a
result of their mass.
 Greater mass, greater gravity; reduce the distance by half,
the force becomes four times as great.
Electroma
gnetic
Nuclear
Force
Electrom
agnetic
Weak
Nuclear
Strong
Nuclear
Gravity
Gravity

Strong nuclear force keeps the nucleus
together.

Weak nuclear force rips apart nucleons into
other particles: beta decay
 Involves the release of neutrinos and positrons
Electro
weak
Strong
Nuclear
Gravity
GUT
Grand Unified
Theory
Gravity
TOE
Theory of
Everything
http://ngm.nationalgeographic.
com/2008/03/godparticle/achenbach-text
Newton’s Laws of Motion
Philosophical
approach but
supported by
observations
Logical analysis
of thought
experiments
Why do objects differ in the way they fall?
A rock would fall faster than a leaf,
Movement of
smoke tends to rise
Movement that
Generally
celestial
and flame always point
upward.
results from an
motion in the
objects: stars,
vertical
Natural
Motion
sun, moon,
planets.
Celestial
Motion
application of
an effort
Violent
Motion
For Aristotle, the natural tendency of an object is to
be in its stable state (stay in its proper hierarchy).
For violent motion to persist, a constant effort must
be exerted on the object.
Wait, there’s a lot of
problems in the natural
setting. I will proceed
with reason and
experiments in my
mind.
First Observation: The roughness of the surface (takes something)
reduces the speed of the object
First Observation: The roughness of the surface (takes something)
reduces the speed of the object
First Observation: The roughness of the surface (takes something)
reduces the speed of the object
Rough surface
Smooth surface
First Observation: The roughness of the surface (takes something)
reduces the speed of the object
Perfectly smooth surface
Second Observation: The motion of an object is affected by a slope
Third Observation: An object that is not moving will stay in that way
unless an effort is exerted on it.
Therefore I can say
that no effort is
required to keep an
object moving. No
effort is required to
keep it at rest.
That means, the natural
tendency of every object
is to maintain its state of
motion.
I will call that property as
inertia.
Inertia comes from the Latin
word iners, which means idle or lazy.
To change state of
motion, apply an effort on
the object.
If it resists, still that is
inertia.
To change state of
motion, apply an effort on
the object.
If it resists, still that is
inertia.
I will make
that into a
law!!
Law of Inertia
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Born premature, three months after his father’s death, Isaac
Newton Sr.
At 3, his mother remarried. He was left at the care of
grandparents. “Threatening my father and mother Smith to burn
them and the house over them.”
Early part of his education… a school drop out… Asperger
syndrome.
At 16, his mother (now widowed again) tried to make a farmer out
of him. The legend of the falling apple.
Returned back to school, “motivated partly by revenge to a
schoolyard bully, he became the top-ranked student.”
Undistinguished as a Cambridge student. Advancement in
mathematics and science and all that came from it, including
calculus and mechanics fundamentally grow from seclusion to
self-study.
Law of Inertia – every object maintains its state of
motion unless a net force acts on it.
Law of Acceleration – the change in the state of motion
of an object is directly proportional to the
net force acting on it, but inversely
proportional to its mass.
Law of Interaction – for every action, there is an equal
but opposite reaction.
Law of inertia – every object tends to maintain
its state of motion unless a net
force acts on it.
So an object
maintains its motion
if there is no net
force or zero total
force acting on the
object.
What is the resultant of the following vectors:
30 newtons East
50 newtons West
20 newtons East
Every object
tends to
maintain its
state of motion
Unless a net
force acts on it
Law of Inertia
Objects at rest
remain at rest.
Objects in motion
remain in motion.
Unless a net force
acts on the object
Law of Inertia
Maintaining
state of motion
No force is
required to
keep it that way
Law of Inertia
A massive object
offers more
resistance to
changes in motion
A massive object
easily maintains
its state of motion
Law of Inertia


Change in the direction
Change in the speed

In short, changes in velocity are changes in
the state of motion.
Changing
state of
motion
A net force
must be acting
on the object
?
Inertia is the resistance of an object to changes
in its state of motion.
 Inertia is the property of matter to maintain its
state of motion.
 Without external forces, an object at rest will
remain at rest.
 Without external forces, a moved object will
proceed in a straight line at constant velocity.
 Inertia is measured by mass.

Changing
state of
motion
A net force
must be acting
on the object
Law of
Acceleration
Acceleration of an object is directly
proportional to the net force applied on it but
inversely proportional to its mass.
Problem: According to Law of Gravitation, greater mass
results to greater gravitational attraction. Then why do
objects fall at the same rate when one experiences
greater force?

Law of Inertia
 ΣF = 0 ; the object has zero acceleration (at rest,
constant velocity

Law of Acceleration
 ΣF = ma; the object is accelerated (the direction of
acceleration is the same as the direction of the net
force)

Law of Interaction
 F action = F reaction

The simple force plus kinematics equation
The Atwood machine
The frictionless slope

Friction plus the three above
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A 1.0kg object is brought to Mercury where
the acceleration due to gravity is 0.38 times
its value on Earth.
 What is the weight of the object on Earth?
 What is the mass of the object on Mercury?
 What is its weight on planet Mercury?

A 10 kg object resting on a frictionless surface
is subjected to two forces: F1=30N directed
east and F2=50N directed west.
 Find its acceleration
 Find its displacement after 10s starting from rest.
What is the acceleration of a 100kg object when
subjected to a 10 N of force? If it starts from
rest, what is its speed after 5 seconds? Ignore
friction.
If a force of 15.0 N directed East acts on a
stationary 5.0 kg mass, what are its
acceleration (include direction), displacement
and velocity after 10.0 seconds?
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Dependent on the surface area that is
perpendicular to the direction of motion
Affected by streamlines
Affected by the speed of the object
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If forces are balanced, the net force is zero.
If the net force is zero, the object is either at
rest or at constant velocity.
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Independent of the surface area; generally not
affected by the surface area
Not affected by speed (though friction is less when
the object started moving)
Mostly dependent on the weight of the object; and,
Nature of the surfaces in contact
A reaction force; does not exist by itself
Opposes the direction of motion or impending motion
f – friction, whether static or kinetic
u- coefficient of friction of the surfaces
in contact
n – normal force
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If the object of analysis is not moving, the
convention for positive and negative
directions applies.
If the object of analysis is accelerated, the
positive direction follows the direction of
acceleration (second law).
m2
m1
What must be the acceleration of
the system on the left if m1 = 5.00 kg
and m2 = 8.00 kg? What magnitude
of tension is present on the string?
Assume that the pulley is
frictionless.
Find the tension between m1=5.00kg and m2=8.00 kg
below as they are pulled by a 500.N of force in the
direction shown, if the coefficient of friction for both
objects is 0.600.
Determine also the acceleration of the system as the
force is applied.
500. N
m1
m2

Block A weighs 2.70N and B weighs 5.40N. The
coefficient of kinetic friction between all surfaces in
contact is 0.25. Find the magnitude of force F
necessary to drag block B to the left at constant
speed.
A
F=?
B
A 3.00 kg object slides down at a constant velocity of 2.00
m/s down a 3o.0o slope. What must be the coefficient of
kinetic friction between the object and the surface?
A 1.00 kg book is pressed
against a vertical wall. If the
coefficient of static friction is
0.250, what minimum
horizontal force is required to
press it at rest on the wall?
F=?

Solve Problem #3 and #9 on pages 102-103.

#4a and 4b
15 minutes

#5a
#5b
#5c
5 minutes
5 minutes
5 minutes
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A 2.00 kg mass resting on a plane inclined at an
angle of 40.0o with the horizontal is attached to
a hanging mass by means of a frictionless pulley
as shown. The hanging mass takes 1.62 seconds
to fall through a distance of 1.52 meters starting
from rest. What is the mass of the hanging mass
if (a) the inclined surface is frictionless? (b) if
coefficient of friction between the sliding mass
and surface is 0.2?

Two blocks A and B are connected by a rope
and attached to the ceiling by another rope.
The mass of block A is 6.00 kg; the mass of
block B is 4.50 kg. Find the tensions in the
rope when the elevator (a) is at rest, (b)
accelerates upward at 2.00 m/s2, and (c)
accelerates downward at 2.00 m/s2