Week of August 21
Week of August 21 PHYS 1500
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This 7 page Class Notes was uploaded by Emma Shoupe on Friday August 26, 2016. The Class Notes belongs to PHYS 1500 at Auburn University taught by Dr. Hebert in Fall 2016. Since its upload, it has received 12 views. For similar materials see General Physics I in PHYSICS (PHY) at Auburn University.
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Date Created: 08/26/16
Physics 1500 – Dr. Hebert Week of August 21, 2016 Free Fall Motion If I hold an apple at some height and let it go, what happens? If I throw an apple straight up, what happens? Freely falling objects – objects moving under only the influence of gravity o Take the acceleration du2 to gravity as a constant a = g = 9.8 m/s o can use the kinematic equations to describe motion the acceleration due to gravity always points toward the surface of the Earth 3 cases of free fall motion – dropping the ball, throwing the ball up, throwing the ball down exa mpl e problem Kinematic equations do NOT depend at all on mass of the object This means, neglecting air resistance, two objects should fall at the same rate regardless of their respective masses o Apollo 15 tested this on the moon Vectors Acceleration, velocity, and displacement are all vectors In one dimension, dealing with vectors is easy: one way is positive, and the other is negative Two dimensions is more difficult Two vectors are equal if they have the same direction and the same magnitude Vectors don’t care where they are, just magnitude and direction To add two vectors graphically (“tip to tail” method) o Step one is to draw the first vector (orange) o Step two is to draw the second vector (blue) so that the tail of the second is on the tip of the first vector o The sum of the vectors is the vector that runs from the tail of the first tosthe tip of the second! Therefore, the sum (green) is A + B (if the 1 was labeled A, and second B) The negative of a vector has the same magnitude as the original, but the opposite direction o So if the blue is B, then the green is -B To subtract vectors, add the negative of the second vector o So the orange vector becomes A (blue) – B (green) When multiplying or dividing by a scalar, a vector is scaled accordingly Vector Components Any vector that we’ll deal with can be written as the sum of vectors parallel to the axes of our coordinate system Magnitudes of these vectors parallel to the axes are called the components of our vectors The three vectors (our original vector and the two parallel to the axes of our coordinate system) make a right triangle, helping us find information about components Example problem o A vector has an x-component of 3 and a y-component of 4. What angle does this vector make with respect to the x- axis? To add two vectors using components, add their x-components together, and their y-components together When multiplying or dividing a vector by a scalar, multiply or divide each of the components by that scalar Example problem August 25, 2016 Example problem Two Dimensional Motion All of this talk about vectors brings us to two dimensional motion For two dimensions, we can define things like displacement, velocity, and acceleration similarly to how it was done before, but now with vectors Motion in Two Dimensions Same kinematic equations as one dimension, but with multidimensional vectors Can be separated into x-components and y- components Two dimensional kinematic motion is equivalent to two separate, independent motions: 1 horizontal, 1 vertical Projectile Motion only Earth’s gravity affects the path of our object (free fall in two dimensions) a y 9.8 m/s and a x 0 an object is given an initial velocity with both horizontal and vertical components at the highest point of an object’s projectile motion, only the vertical velocity is necessarily zero Notably, the horizontal velocity will be the same at the top of the motion as it was at the beginning of the motion The vertical acceleration is NOT ZERO at the top of the motion Example problem o Alabama punter kick bot kicks a ball with an initial velocity of 29 m/s at an angle of 80 degrees above ground after it leaves his foot. How far horizontally has the ball gone once it reaches the ground? Assume the ball left the kick bot’s foot at ground level. Another problem o A ball is thrown with an initial speed of 10 m/s at an angle of 20 degrees above the x-axis. How far horizontally has the ball gone once it reaches its highest point? Final problem o I honestly didn’t write the word problem down. This one was about the monkey in the tree, and if we were hunting the monkey would we want to aim above the monkey, at the monkey, or below the monkey? I tried my best to follow the math we did in class, so bear with me.
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