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Projectile Motion 9/27/11 Bellwork • 3 ways to accelerate: • - Speeding up (gas pedal) • - Slowing down (brake pedal) • - Turning (steering wheel) Throwing a ball in the air • On the way up: • velocity decreases • acceleration stays the same. • At the top of the • velocity zero throw: • acceleration stays the same. • On the way down: • velocity increases • acceleration stays the same. Throwing a ball in the air • The velocity changes. • The acceleration is constant, it stays the same 9.81 m/s/s throughout the flight. Projectiles • Projectile are objects where gravity and air resistance are the only forces acting • The force of gravity does not affect the horizontal component of motion • A projectile’s horizontal component is independent of the vertical component • Projectiles travel with a parabolic trajectory Mythbusters • Dropped vs. Fired Bullet • http://dsc.discovery.com/videos/mythbuste rs-dropped-vs-fired-bullet.html • http://www.youtube.com/watch?v=D9wQVI EdKh8 Air Resistance • Air Resistance: A force of friction that acts on an object moving through the air • For projectile motion we will neglect or assume that air resistance is extremely small Horizontal Vertical Motion Motion Force No Yes, the force of gravity acts downward Acceleration No Yes "g" is downward at 9.81 m/s/s Velocity Constant Changing (by 9.81 m/s each second) Projectile • What happens to a projectile’s horizontal and vertical velocity? • What happens to a projectile’s horizontal and vertical displacement? • Example: An object with a initial horizontal velocity of 20 m/s to the right and vertical velocity of 0 m/s. Velocity Time Horizontal Vertical Velocity Velocity 0s 20 m/s, right 0 m/s 1s 20 m/s, right 10 m/s, down 2s 20 m/s, right 20 m/s, down 3s 20 m/s, right 30 m/s, down 4s 20 m/s, right 40 m/s, down 5s 20 m/s, right 50 m/s, down Displacement Time Horizontal Vertical Displacement Displacement 0s 0 m, right 0m 1s 20 m, right 5 m, down 2s 40 m, right 20 m, down 3s 60 m, right 45 m, down 4s 80 m, right 80 m, down 5s 100 m, right 125 m, down A falling object A falling object Projectile Animation • http://ngsir.netfirms.com/englishhtm/Throw ABall.htm Projectile Motion 9/28/11 Components • Component: the projection of a vector quantity along a perpendicular axis Components Horizontal • Right = +x • Left = -x Vertical • Up = +y • Down = -y Projectile Quantities • Displacement (m) dx = horizontal displacement dy = vertical displacement • Velocity (m/s) vx = horizontal velocity vy = vertical velocity Projectile Quantities • Acceleration ax = 0 m/s2 (no horizontal accel.) ay = -9.81 m/s2 or “g” • Time (s) t = time does not depend on direction (scalar) is the same for horizontal and vertical components Projectile Problems 1. Draw a sketch of the problem to determine horizontal and vertical components 2. Use a T-Chart to organize the problem 3. Time (often needed to be solved for 1st) is a scalar, it is the same for the horizontal and vertical components Formula Cards • Component axis • Projectile (horizontal) • Projectile (vertical) Homework • Example of velocity vectors of an object going up and down • Example of projectile motion problem

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posted: | 12/21/2011 |

language: | English |

pages: | 23 |

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