Newton

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• Newtons 1st and 2nd laws of Motion

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4 Forces of the Universe

• Nuclear Strong forces holding the nucleus of an
  atom together (gluon)
• Weak Forces as a result of some atoms that
  decay the nucleus ( radioactive )
• Electromagnetic a force based on electricity,
  magnetism and light properties
• Gravitational The weakest force caused by the 2
  factors, MASS and DISTANCE

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Mechanical Forces

• Inertia Newtons First Law, net or unbalanced
  force is needed to change the state of motion
• Friction the contact force that acts to oppose
  sliding motion between surfaces
• Normal the contact force exerted perpendicular
  to the surface contact
• Tension the pull exerted by a cable when
  attached to a body
• Compression the push exerted to the object
• Weight force of attraction due to distance from
  the center of the earth and mass of the object
• Units are Measured in NEWTONS ( N )

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Newton's First Law of Motion ( inertia )

• An object at rest tends to stay at rest and an
  object in motion tends to stay in motion with the
  same speed and in the same direction unless acted
  upon by an unbalanced force.

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Stationary and Moving objects
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Balanced and Unbalanced Forces

• The book is said to be at equilibrium. There is
  no unbalanced force acting upon the book and thus
  the book maintains its state of motion

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Balanced and Unbalanced Forces

• The book is not at equilibrium and subsequently
  accelerates

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Newtons Second law of motion

• The acceleration of a body is directly
  proportional to the net force on it and inversely
  proportional to the mass. ( F ma )
• Unit of Force kg-m or N (Newton)
• s2
• Calculation
• mass of an apple is 100g or .1 kg
• F ma (.1kg) (10 m/s2) 1 kg-m/s2 1 N

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Sample Force Problem 1

• Using Newtons Second law of Motion ( the
  acceleration of a body is directly proportional
  to the net force on it and inversely proportional
  to the mass, F ma).
• What net force is
• required to accelerate
• a 1500 kg car
• at 3.00 m/s2?

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Solution Problem 1

• F m a
• F 1500 kg x 3.00 m/s2
• F 4500 kg-m/s2
• or
• F 4500 N

Given m 1500 Kg a 3.00 m/s2 Find F ?
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Static Balance (free body) Problem 2

• Forces of 10 N and 15N are arranged according to
  diagram. What is the net force on this object.
  What is the rate of acceleration of the 12 Kg
  object?

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15
12 Kg
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Solution 2

• Given
• Force 10 N and 15 N in opposite directions
• Mass 12 Kg
• Find
• Net Force
• Acceleration

Net Force F1 - F2 15N 10N 5 N
F ma 5N 12 Kg (a) 5N
a 12 Kg 0.417 m/s2 a
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Sample Question 3

• The figure shows a block that is being pulled
  along the floor. According to the figure, what is
  the acceleration of the block?

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Solution Problem 3

• F m a
• 40N 20 kg (a)
• 2 m/s2 a

Given m 20 Kg Ffriction 10 N Fpull 50
N Find a ?
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Sample problem 4
A 50-kg child on a skateboard experiences a 75-N
force as shown.
What is the expected acceleration of the child?
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Solution Problem 4

• F m a
• 75 N 50 kg (a)
• 1.5 m/s2 a

Given m 50 Kg Fpush 75 N Find a ?
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Uniform Circular Motion

• Circular motion at a constant
• speed HAS an ACCELERATION!
• Keeping the magnitude of the velocity constant,
  but changing the direction will create a change
  in acceleration
• Using vector addition, a centripetal v2
• 
  r

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Sample Problem 3

• During a hammer throw, an athlete rotates a 7.00
  kg hammer tied to the end of a 1.3 m chain. The
  hammer moves at the rate of 3 m/s in a circle.
• What is the centripetal acceleration of the
  hammer
• What is the tension in the chain?
• If the chain breaks at the point shown which
  direction will the hammer fly?

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Solution Problem 3

• m 7.00 kg v c 3.0 m/s r 1.3 m
• a c v2 / r
• a c (30 m/s)2 / 1.3 m
• a c 900 m2/s2 / 1.3 m
• a c 692.3 m/s2
• F c m a c
• F c 1.3 kg ( 692.3 m/s2)
• F c 900 N _at_ the tangent (direction 2)

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Summary

• Forces are invisible measurements that explain
  the states of motion
• Newton derived laws of motion that explained the
  way things move.
• Forces can be balanced (equilibrium) or
  unbalanced (acceleration).
• Uniform circular motion is accelerating because
  of the constant change in direction