Physics 151 Week 4 Notes
Physics 151 Week 4 Notes PHYS151
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This 4 page Class Notes was uploaded by Lindsey Notetaker on Saturday September 24, 2016. The Class Notes belongs to PHYS151 at University of Nevada - Las Vegas taught by Dr. Pang in Fall 2016. Since its upload, it has received 24 views. For similar materials see General Physics I in Physics at University of Nevada - Las Vegas.
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Date Created: 09/24/16
General Physics 151. Week 4 Notes (September 19, 2016) Chapter 4: Dynamics of a Particle Key to my notes: all notes that are taken from the lecture will be the first section, notes I take from the textbook will be the second section, and the vocabulary words from the chapter with definitions will be the last sections! (: Lecture Notes Point particle vs. extended objects If center of weight is all on one side, it is dangerous A point particle description of an object is valid if the size of the object is much smaller than the length scale of the dynamics involved, or ever point on the object behaves the same Equivalent between one dimensional and tangential motion o Force of x=mass X acceleration of x o Force of t= mass X acceleration of t o Acceleration of t=limit as change in t reaches 0 in the change of speed of object/change in time Uniform circle means the speed is constant Velocity is the tangential line of curve If speed is constant on a circle then velocity is found by (circumference [2*pi*r])/(period [T]) Velocity is not constant neither is acceleration=0 because it is changing direction The centripetal force is provided by static friction with o Centripetal force = mass X acceleration of centripetal =(mass X velocity squared)/radius = static friction What is most effective to increase safety on the road? o Reducing speed of car o Improving friction coefficient o Increasing the radius of the turn Centripetal force =(normal force X sine of theta) +/ (static/kinetic friction X cosine theta) o If car is not sliding the normal force can be obtained by (normal force X cosine theta) = (mass X gravity) +/ (static friction X sine of theta) If the circle is not uniform then you can fine the acceleration of the centripetal force by (velocity squared)/(radius) Kepler’s law of planetary motion is NOT a fundamental law o Elliptic orbits with the sun at a focal point o Equal areas over the elapsed time o Period squared is similar to radius cubed Fictitious force equals negative mass X inertial acceleration Centrifugal force equals mass X (velocity squared/radius ) o This is for a uniform rotating reference frame Page 1 of 4 General Physics 151. Week 4 Notes (September 19, 2016) o If made to be the same weight on earth the equation is mass X gravity The thrust on the rocket from burning fuel is found by mass X (the limit of time as it approaches zero of the [change in velocity]/[change in time]) o Velocity equals u X ln(mass initial/mass overall) – gravity High speed limits is found by (c/2)pAV^2 o C depends on the medium o P is the density of the medium o A and v are the cross sectional area of the object Low speed limits is found by bv o B for a square is 6piRn R is the radius N is the coefficient of viscosity of medium o V is velocity Textbook Notes Even big objects can be looked at as a point if the all other points move in the exact same way If a point is moving in one direction, its equation is force in the x direction = mass X acceleration of x If the object has a curve then you take the tangent line at the curve and find the force of the tangential line and treat it as a one dimension problem o To find the acceleration of the line, you take the limit as the tangent line nears 0 and find (change in velocity)/(change in time) A uniform circle means that the speed of the circle does NOT change o For a uniform circle the velocity can be found by (2 *pi*radius)/period Friction can either be static or kinetic, going down (plus sign) or going up (minus sign). If the object is not sliding when it is going in a circle then the normal force is (normal force X cosine theta) = mass X gravity +/ (static friction X sine theta) If the circle is not uniform then you can solve centripetal force by o Force of centripetal = tension +/ (mass X gravity X sine theta) Can also be written (mass X velocity squared)/ radius air resistance is always against the tangential acceleration o this causes the object to decrease you can always ﬁnd an equivalent circle for any point on the path o If the point is curve then for each curve, you can make it part of a circle to find the distance or velocity The dynamics of a planet is therefore dictated by the gravitational attraction between two point particles Page 2 of 4 General Physics 151. Week 4 Notes (September 19, 2016) o Force = (Gravitational constant)X[(mass of sun X mass of planet)/(distance between the planet and the solar center)] For a rocket in space where gravity does not affect it, the speedmass ration is: o Velocity= (initial speed ) + [(rate of burning the fuel) X (natural log of ((final mass of rocket)/(initial mass of rocket))] For a rocket in space where gravity does affect it, the speedmass ration is: o [(rate of burning the fuel) X (natural log of ((final mass of rocket)/(initial mass of rocket))] – (gravity X change in time) For a rocket in space where air resistance does affect it, the speedmass ration is: o (drag coeﬃcient of air resistance/2) X (density of air) X (crosssectional area of the rocket) X (speed squared) When an object is falling at very high speeds you find the speed by using: o (mass X gravity) (drag coeﬃcient of air resistance/2) X (density of air) X (crosssectional area of the rocket) X (speed squared) When an object is falling at low speeds you find the speed by using: o [6 X pi X (radius of the sphere) X (coeﬃcient of viscosity of the ﬂuid)] X velocity Vocabulary Words Note: These are in order as they showed up in the chapter, not in alphabetical Center of Mass: the geometric mean center of the mass distribution of an extended system, known as the Centripetal Direction: the change of motion along the tangential direction and the change of motion in the direction perpendicular to the tangential, toward the center of curvature Kepler’s First Law: states that all the orbits of the planets are elliptic with the sun at a focal point of the ellipses Kepler’s Second Law: states that for a given planet, the area swept by its radius from the sun is the same for any equal elapsed time Kepler’s Third Law: states that square of the period of a planet is proportional to the cube of its mean distance from the sun Fictitious Force: a fake force that is felt when comparing to a noninertial reference frame Page 3 of 4 General Physics 151. Week 4 Notes (September 19, 2016) Apparent Weight: when an object experiences a greater normal force than normal and it affects what their weight reads Page 4 of4
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