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4 Force Physics IVC

# 4 Force Physics IVC - Newton's First Law Law I Everybody...

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Newton’s First Law Law I Everybody continues in its state of rest, or in uniform straight- line motion, unless a force acts upon it. Object at rest remains at rest unless a force acts upon it. Force acted on red ball: Cause and effect.

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Less friction object goes further before slowing. Note the puck below would go forever without the frictional forces as we see once we turn on the air to the air glider table. This can be demonstrated on the air-glider track.
Newton’s Second Law Σ F = m a The sum of forces on an object, cause the object to accelerate—velocity changes with time .

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To every action there is a reaction. Newton’s Third Law: Force of hand pushes on wall. Wall Pushes back with the same force, but not same accelerations would result if wall moved. Why not?
Applying Newton’s Laws The mathematical expression above says: the sum of forces on the object equals the mass times acceleration of the object. Σ F = m a ΣF x = ma x ΣF y = ma y ΣF z = ma z Note if the object is in equilibrium the all sums of forces equal zero, i.e. no acceleration: Σ F = m a = 0 Force is a vector. We have learned vectors must be analyzed component-wise.

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1) Write down what you are trying to solve? 2) Draw a picture of problem 3) Write down knowns and initial conditions of problem 4) Choose appropriate coordinate system 5) Draw free body diagrams 6) Write out F = ma in component form 7) Draw component forces 8) Solve F = ma for acceleration or other related variables and information. Setup for Force problems: E.g. How much force is needed? A = 5, B = 2x, z = 9 x y F x = ma x F F x
Newton’s third Law A force acting on a body is always the result of its interaction with another body. Thus forces always form in pairs . Newton’s third law of motion: If Body A exerts a force on body B (an action), then body B exerts a force on body A (a reaction). These two forces have the same magnitude but are opposite in direction. These two forces act on different bodies. F AB = - F BA

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Action-reaction pair. Foot on ball, ball on foot.
Two forces are acting on same object. Hence not action- reaction force pairs. Pair of forces acting equal and oppositely on each other. Hence are action-reaction pairs.

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An object moving at a constant velocity does not need a force to keep it moving. This is essentially the First Law of Motion: An object will remain in whatever state of motion it is in unless it is acted on by an outside, unbalanced force. In this Exploration, you will investigate what happens when there is an external, unbalanced force acting on an object. The first law also lets us know if we are in an inertial frame or not. For if you see something accelerate without a force acting the object, then you are not in an inertial frame of reference. I.e. and airplane taking off on the runway.

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4 Force Physics IVC - Newton's First Law Law I Everybody...

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