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This 3 page Class Notes was uploaded by Udbluehen03 on Saturday October 8, 2016. The Class Notes belongs to PHYS201012 at University of Delaware taught by Gogoladze,Ilia in Summer 2016. Since its upload, it has received 6 views. For similar materials see Introductory Physics I in PHYSICS (PHY) at University of Delaware.
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Date Created: 10/08/16
Forces of Friction - To slide one such surface across another requires a force larger enough to overcome the resistance of microscopic hills and valley bumping together. This is the origin of the force we call friction - When an object is in motion on a surface or through a viscous medium, there will be a resistance to the motion. - This is due to the interactions between the object and its environment. o This resistance is called the force of friction. - Force that slows down or stops motion. - Force that helps to start motion. - Problem-Solving Hints o Conceptualize Draw a diagram Choose a convenient coordinate system for each object o Categorize Is the model a particle in equilibrium? If so, ????F = 0 Is the model a particle under a net force? If so, ???????? = ma Kinetic friction - Is the friction encounter when surfaces slide against one another with a finite relative speed - Fk acts to oppose the sliding motion at the point of contact between the surfaces - The kinetic frictional force is also independent of the relative speed of the surfaces, and of their area of contact - The force of kinetic friction is proportional to the magnitude of the normal force, N o Fk = µkN - µk o coefficient of kinetic friction o always positive o typically, between 0 and 1 - the normal force is greater than the weight if someone pushes down on the bricks, and this would cause more friction, or less than the weight if the bricks are placed on an incline - the greater the µk, the greater the friction - the smaller the µk, the smaller the friction Static Friction µs) - Coefficient of friction does not depend to the mass and area, but frictional force does - f s,max =µ s N Tension - When you pull on a string or rope, it becomes taut. We say that there is tension in the string - The tension in a real rope will vary along its length, due to the weight of the rope - An ideal pulley is one that simply changes the direction of the tension but not magnitude of the tension - T = mg Connected Objects - When forces are exerted on connected objects, their accelerations are the same. - If there are two objects connected by a string, and we know the force and the masses, we can find the acceleration and the tension Hook’s Law - Hooke’s law for springs states that the force increases with the amount the spring is stretched or compressed - F = -kx - The constant k is called the spring constant and it is measured in ????/????. Uniform Circular Motion, Acceleration - A particle moves with a constant speed in a circular path of radius ???? with an acceleration. - The magnitude of the acceleration is given by ???? 2 - ⃗????= ???? - The centripetal acceleration,????⃗ , is directed toward the center of the circle. ???? - The centripetal acceleration is always perpendicular to the velocity Uniform Circular Motion, Force - A force????⃗, is associated with the centripetal acceleration. - The force is also directed toward the center of the circle. - Applying Newton’s Second Law along the radial direction gives ???? 2 - ???????????? ???????? ???????? = ???? ???? - A force causing a centripetal acceleration acts toward the center of the circle. - It causes a change in the direction of the velocity vector. - If the force vanishes, the object would move in a straight-line path tangent to the circle Horizontal (Flat) Curve - Car in equilibrium in the vertical direction. - The force of static friction supplies the centripetal force. - Car in uniform circular motion in the horizontal direction - The maximum speed at which the car can negotiate the curve is: - ???? = µ ???????? √ ???? - Note, this does not depend on the mass of the car.
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