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## Chapter 2 Motion in One Dimension

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**An object can be moving with respect to one object and at**the same time be at rest or moving at a different speed with respect to another.**Frame of Reference**• Is the point with which a motion is described.**Depends upon how you look at it?**If you look at it from the point of view with the room, most of you are not moving.**If you look at it from the point of view from outer space,**then you are moving as fast as the earth is rotating.**Or from out side the solar system, the earth is moving**around the sun at a speed of approximately 100,000 km/hr.**Vector**A physical quantity that has both magnitude and direction.**Ex: 10 km, North**15 m/s, SW**Scalar**A physical quantity that has magnitude, but no direction.**Ex: 55 km/hr**19 m**Distance**How far an object has moved. No direction, therefore a scalar. Ex: 20 km**Displacement**The change in position of an object**Displacement**= Change in position = Final position – Initial position**Displacement has a specific direction, therefore it is a**vector.**On the x-axis displacement to the right is (+) and**displacement to the left is (-). On the y-axis displacement upwards is (+) and displacement downwards is (-).**Speed**Measure of how fast something is moving.**Is the distance covered per unit of time.**ex: 72 km/hr or 20 m/s**Speed Units**• m/s, km/hr, or cm/s, same as velocity units. • Since speed has no direction, it is a scalar.**The fast speed possible is the speed of light.**Which is 3 x 108 m/s (299,792,458 m/s)**Instantaneous Speed**• Is the speed of an object at any instant.**Instantaneous Speed**• Is the speed of an object at any instant. • Ex: speedometer reading**Average Speed**The total distance divided by the time interval during which the displacement occurred. (Vavg)**Change in position**Vavg = ---------------------- Change in time total distance = ----------------------- time interval**x**D v t D avg**The cheetah averages 70 m/s over 30 seconds. How far does it**travel in those 30 seconds?**Velocity**Is the rate of change of displacement. • It is speed with a direction. (vector)**The Vavg can be (+) or (-), depending on the sign of the**displacement.**Ex 1: During a trip, a plane flies directly East with an**average velocity of 35 m/s. What distance does the plane cover in 45 minutes?**G: Vavg = 35 m/s, D t= 45 min= 2700 s**U:D X = ? E: D X = (Vavg)(D t) S: DX=(35m/s)(2700s) S: D X = 94,500 m, E**With your group, work together to solve practice problems:**2, 4, and 6 on page 44 (HP). Do these problems in your notes. I will check for them in the notebook check. Also use the GUESS method.**2) 3.1 km**4) 3 hr 6a) 6.4 Hour 6b) 77 km/hr South**Uniform Motion**Both velocity/speed and direction of the body/object remain the same.**Accelerated Motion**• Is when the velocity/speed of the object is changing.**Acceleration (aavg)**Is the rate of change of velocity. How fast you change your velocity**aavg has direction and magnitude; therefore, it is a vector.****Change in Velocity**aavg = --------------- Time interval for change