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What is Motion? Chapter 9 Section 1 and 3

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Reference point a place or object used for comparison to determine if something is in motion.

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Suppose you are standing on a sidewalk and your friend rides past you on her skateboard. –Which one of you is moving relative to the Earth? –Are you moving relative to your friend?

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Motion an object is in motion if it changes position relative to a reference point. An object moves when its distance from another object is changing. Whether an object is moving or not depends on your point of view (reference point).

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Speed The distance an object travels in one unit of time is its speed. Speed = Distance Time Units of Speed = (m/sec) or (km/hr) Average speed = total distance total time

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Sample Problem: At what speed did a plane fly if it traveled 1760 meters in 8 seconds?

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Practice Problems: A car travels 240 kilometers in 3 hours. What is the speed of the car during that time? The speed of a cruise ship is 50 km/hr. How far will the ship travel in 14 hours? A cyclist travels 32 km during the first 2 hours of riding, and 13 km during the next hour. What is the average speed of the cyclist?

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Velocity speed in a given direction. Velocity = Distance Time Note that the velocity equation is the same as the speed equation

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Graphing motion Always use a distance vs. time graph (distance on the vertical or y-axis and time on the horizontal or x-axis). Slope – tells you the rate of change (speed). slope = rise run

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Acceleration the rate of change in velocity. Refers to increasing speed, decreasing speed, or changing direction. (a)=Final Velocity (fv)-Initial Velocity (iv) Time (t) a = fv – iv t Units for Acceleration: km/hr2, km/hr/s or m/sec2

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Practice Problems: A roller coaster is moving at 25m/sec at the bottom of a hill. Three seconds later it reaches the top of the next hill, moving at 10m/sec. What is the deceleration of the roller coaster? A car is traveling at 60km/hr. It accelerates to 85km/hr in 5 seconds. What is the acceleration of the car?

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Graphing Acceleration Velocity vs. Time –Velocity on y-axis –Time on x-axis The slope of the line gives you the acceleration of the object.

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Final Practice Problems One jet plane is flying east at 880 km/h, and another plane is traveling north at 880 km/h. Do they have the same velocities? The same speeds? Explain. A swimmer speeds up from 1.1 m/s to 1.3 m/s during the last 20 seconds of the workout. What is the acceleration during this interval? Describe three different ways to change your velocity when youre riding a bicycle. An object is said to be accelerating if it ___________. a) speeds upc) changes direction b) slows down d) all of these

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