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Unit 4 |
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Newton’s Laws of Motion |
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1st law - an object will maintain its state of
motion as long as the forces acting on the object are balanced (law of
inertia) |
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2nd law - an object will be accelerated at a
rate inversely proportional to its mass by an unbalanced force ( F = m a ) |
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3rd law - for every action there is an equal and
opposite reaction (action-reaction) |
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Inertia - the ability of an object to maintain its state of
motion |
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depends on: mass, shape, position … |
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Equilibrium - a state of motion in which all
forces are balanced |
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SF = 0 |
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no net force, no acceleration |
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Vector addition |
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sine |
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cosine |
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tangent |
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Pythagorean Theorem |
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law of sines, law of cosines |
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Problem Solving Steps |
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Identify Problem |
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Sketch a Free Body Diagram |
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If 3 forces: If more than 3: |
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force
triangle to scale “tip to tail” OR |
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OR law of sines &
cosines components |
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Solve for unknown forces |
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Evaluate results (check magnitude and direction) |
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Concurrent forces - all forces have a common
point of application |
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S Fx = 0 |
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S Fy = 0 |
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Nonconcurrent forces - forces do not have a
common point of application |
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S Fx = 0 |
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S Fy = 0 |
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S t = 0 |
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Torque - the product of the applied force (F)
and the moment arm ( r^) . |
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Concurrent forces - all forces have a common
point of application |
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S Fx = 0 |
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S Fy = 0 |
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Nonconcurrent forces - forces do not have a
common point of application |
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S Fx = 0 |
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S Fy = 0 |
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S t = 0 |
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Center of Gravity - point at which the entire
weight of an object could be balanced |
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c.g. = S t
/ S F |
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2nd law - an object will be accelerated at a
rate inversely proportional to its mass by an unbalanced force ( F = m a ) |
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Distance (displacement), speed (velocity),
acceleration, time |
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Weight - the force due to gravity |
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Measured in newtons (N) or pounds (lbs.) |
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Mass - the amount of matter |
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Measured in kilograms (kg) or slugs |
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The net force acting on an object will cause a
‘change in motion’ (acceleration) inversely proportional to the mass of the
object. |
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Thrust - Drag = m a |
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Motion in which the speed is constant but
direction is constantly changing. |
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A constant change in velocity. |
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Constant acceleration. |
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A constant acceleration (change in velocity)
must be caused by a constant force. (Newton’s 2nd law) |
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A constant acceleration (change in velocity)
must be caused by a constant force. (Newton’s 2nd law) |
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A constant acceleration (change in velocity)
must be caused by a constant force. (Newton’s 2nd law) |
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linear speed vs. rotational speed |
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centripetal acceleration |
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Centripetal Force is necessary for uniform
circular motion. (constant change of direction) The speed and radius of
rotation determine the acceleration. |
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Fc = m ac Fc
= m v2 / R |
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Petal means seeking or toward. Therefore
centripetal means toward the center. |
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Fugal means fleeing or away from the center.
Therefore centrifugal means away from the center. |
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There is no force on a rotating object away from
the center. The object may itself exert a force away from the center.
(Newton’s 3rd law) |
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For every action there is an equal but opposite
reaction. These DO NOT CANCEL because they act on different objects. |
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For example: Thrust - the propeller applies a
force to the air, the air applies an equal but opposite force to the
propeller . |
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Static friction (starting) |
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Kinetic friction (sliding) |
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F = m N |
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Always opposite direction to motion or forces
attempting motion |
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Directly proportional to the Normal force |
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m = coefficient of friction determined by the
type of surfaces in contact |
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Notes