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25 Cards in this Set
- Front
- Back
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force definition
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push or pull on an object
force has direction and magnitude |
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dynamics
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connection between force and motion
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newton's first law of motion
aka law of inertia |
every object continues in its state of rest or of uniform velocity in a straight line as long as no net force acts on it
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inertia
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tendency of an object to maintain its state of rest or uniform motion
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inertial reference frames
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law only holds in inertial reference frames
if it doesn't hold it is a noninertial reference frame |
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mass definition
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measure of inertia of an object
mass does NOT equal weight mass is not a force, it is a property of the object itself weight is a force upon the object |
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newton's second law of motion -definition
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acceleration of an object is directly proportional to the net force acting on it, and inversely proportional to its mass. the direction of the acceleration is in the direction of the net force acting on the object
relates description of motion to cause of motion - how forces affect motion also valid only in inertial reference frames |
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newton's second law of motion -equation
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sigmaF = ma
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force definition
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action capable of accelerating an object
force is a vector with magnitude and direction |
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N
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newton- unit of force
kg*m/s^2 force required to impart an acceleration of 1m/s^2 to 1kg |
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Newton's third law of motion - definition
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Whenever one object exerts a force on a second object, the second exerts an equal force in the opposite direction of the first
where forces come from - a force exerted ON an object is exerted BY another object |
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Newton's third law of motion - equation
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Fx=-Fx
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rocket propulsion - how it works
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rocket exerts force ON gases, expelling them gases exert equal an opposite force on the rocket, which propels it forward
gases pushing on the rocket NOT by gases rushing out back pushing the ground or atmosphere |
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what makes a car go forward or a person walk forward
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force of ground on the tires, force on person by ground
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weight - definition and equation
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weight=FG=mg
magnitude of the force of gravity on an object g=9.80 m/s^2 = 9.80 N/kg |
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contact force
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force that occurs when 2 objects are in contact
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normal force
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normal=perpendicular
contact force that acts perpendicular to common surface of contact |
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normal force and weight on an object- Caution!
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normal force and weight on an object are NOT action-reaction pairs because they are forces on a single object
action reaction is always a force BY ONE object ON ANOTHER |
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vertical - definition
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direction in which objects fall
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horizontal - definition
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surface on which a round object won't start rolling
gravity has no effect |
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net force
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vector sum of all forces acting on an object
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problem solving
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1.draw sketch
2. draw a diagram of all forces acting on the object in question and only on the object in question if 2 objects are in questions separate diagrams are needed 3. resolve into vertical and horizontal 4. apply second law of motion to horizontal and vertical motions separately 5 solve for unkwon(s) |
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cords and tension
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FsubT tension is the force a cord exerts on an object
cords have negligible mass and force is transmitted undiminished cords can only pull, not push forces pulling on the cord at its 2 ends must equal to 0 |
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kinetic friction
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sliding friction
Ffr = uk FN not a law, but an experimental relation not a vector equation - forces are perpendicular uk - coefficient of kinetic friction depends on both surfaces |
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static friction
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force parallel to surface/normal force on an object that is not moving
once object starts to move, kinetic friction takes over Ffr is lees than or equal to us * FN static friction is greater than kinetic friction - so it's easier to keep an object in motion than to get it moving |
