Transcript CHAPTER 5 NOTES - School District of La Crosse

CHAPTER 5 NOTES
KONICHEK
I. Dynamics- why objects move the way
they do,
A.. kinematics studied how objects move
1. Isaac Newton- First to study the
causes of accelerations
a. summarized them in 3 laws of
motion
Welcome to the concept of
universal forces
II.Force- a push or pull
 A. 4 types of forces
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1. Gravitational- the force of
attraction between all objects
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a. weakest of the 4 forces
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b. carried by the graviton
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1. only become significant with
large amounts of mass.
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2. Electromagnetic forces- the forces caused
by the charges between particlesa. carried by the photon
b. produced by the motion of charged
particles. The magnetic field and the electric
field vibrate at 90 to each other.
1. act as a single force- electromagnetic
force
► 3.
Strong nuclear- this is the force which
hold the nucleus together
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a. strongest of the 4 forces- 100 times
stronger
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b. acts for very short distances
► 4. Weak force-a form of EM forces
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a. decay of some types of nuclei
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Grand unified theory- at some
point in time all 4 forces acted as a
single unified force
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1. Planck time 10-43 this is the
conditions which may explain the big
bang
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a, all know physics breakdown
at this point
Isaac and his 3 laws
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III.Newtons Laws of Motion( Galileo based)
A. First law- an Object with no force acting on it moves with a constant
velocity.
1. unbalanced forces- This is a force which causes motion to occur.
2. Balanced forces- equilibrium- the sum of all the forces acting on an
object is zero
3. Must assign signs to show the direction of the force
a. positive forces to the right
b. negative forces to the left
4. To find the net force it is the summation of all the forces acting on
the object.
a. if the net force is zero the velocity is zero and no motion
results.
5. Expanding the first law- an Object with no net force acting on it
remains at rest or moves with a constant velocity in a straight line.
EXAMPLE OF FIRST LAW
POOR LITTLE TEST TUBE
Mr. Konichek testing the First Law.
wow man!
B. Second Law- The acceleration of a body
is directly proportional to the net force and
inversely proportional to its mass
1. F=ma
2. as force increases acceleration
must increase
3. as mass increases and force is
constant the acceleration must decrease
4. The net force on an object
causes an acceleration
5. unit for force- 1 Kgm/s2 = 1
Newton( N)
HEY- 2ND LAW EXAMPLES
C. Sample problems
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1. what is the net force of an
object accelerating at 5m/s2 and has a
mass of 500Kg?
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2. What is the acceleration of a
3000Kg truck which has a force of 8000N
applied to it?
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Finding force when acceleration
must be calculated, given the final
velocity, and distance,
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1.initial velocity is zero( Impulse
force)
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a. Use Vf2= Vi2+ 2ad, solve for a:
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a= Vf2-Vi2/ 2d
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substitute into F=Ma
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F= M(Vf2 –Vi2)/2d
PRACTICE, PRACTICE
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1. example - a cannon ball with a mass
of 60Kg is fired from a cannon at a
velocity of 70m/s. the cannon is 2.5m
long, assuming the force and acceleration
are constant. What would be the force on
the cannon ball while it is in the barrel of
the cannon?
ASSIGNMENT- PAGE 92 1-4
► E.
Third Law of Motion- For each action
force there is an opposite and equal
reaction force.
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1. walking, rocket blasting off.
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2. only the force exerted on the
object will cause an acceleration.
Kick of a gun
• IV. Using Newton's Laws
• A. Mass and weight•
1. mass- the quantity of matter
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2. weight- The gravitational force
exerted by a large body
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a. w=mg
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b. On earth. 1kg9.8m/s2= 1
Newton
B. Types of masses
1. Inertial mass- The ratio of the net force
exerted on an object and it’s acceleration
a. Mi= F/a
2. Comparison method- Compare the mass
of unknown quantity to one of known quantity on
a balance.
a. When the pans balance the masses
are equal.
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C. Friction- This is the force between two
surfaces which are in contact with each other.
1. Causes- all surfaces are rough, when
they rub against each other there is a weak
electromagnetic bond set up between the
surfaces
2. Static Friction- This is the force which
opposes the start of motion
a. Have the maximum values of
frictional forces
b. Must overcome the static friction
when moving something.
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3. Sliding friction-The force between sliding surfaces
a. Less that the static friction
4. Force of friction( assignment P 99- 9 and 10)
a. depends upon the force pushing the surfaces
together and the nature of the surfaces in contact.
1. Ff= MuFn (F=μFn)
a. μ(Mu)= coefficient of friction
b. Fn= Normal force- perpendicular to the
line of motion
1. It’s the sum of all the downward
forces on the object.
b. We will assume the coefficient of sliding friction
is independent of the surface area and velocity.
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The net force causes acceleration
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1. The acceleration of an object is the result
of the net force acting on the object.
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2. The net force is the vector sum of the
applied force and the frictional force
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a) Fnet= Fapplied + Ffriction
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b) Fnet=Fground+ weight
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c) throwing up the stone Fn= Fobject+
Weight
FREE FALL
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E. The fall of bodies in air
1. In a vacuum all objects accelerate at the
same rate
2. In the atmosphere objects will fall at
different rates because of air resistance
a. drag- The force of the atmosphere
against a moving object- form of friction
3. depends on:
a. size, shape, the air density, and the
speed of motion.
F. Universal Gravitation- all objects with
mass attracts themselves directly
proportional to the masses and inversely
proportional to the square of the distance.
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1) F= Gm1m1/R2
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2) G=6.67x10-11Nm2/kg2
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4. Falling objects gravity is pulling harder than the
drag
a. as the velocity of the object increases
the drag increases until the drag force equals the
pull of gravity... net force is zero
1. the object stops accelerating...
terminal velocity
2. a falling parachutist spread eagle
falls about 60m/s
3. with the chute open 5m/s.
PRACTICE PROBLEMS ASSIGNMENT
PAGE 105 :1, P106 :4,6,8,9,10, 12,15,p 10722 ,24