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Published byVincent Maxwell Modified over 4 years ago

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The speed of an in-line skater is usually described in meters per second. The speed of a car is usually described in kilometers per hour.

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Speed and Velocity Speed- the distance traveled divided by the time taken to travel the distance. formula: speed = distance/time (s=d/t) units: meters per second (m/s)- standard SI unit, (km/hr), (cm/s) A swimmer who swims 100 m in 56s 100 m ? 56s d d= s= t= s t

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A cyclist travels a total distance of 45 km at an average speed of 15 km/hr. How long did it take for him to go this distance? 45km 15 km/hr ? d d= s= t= s t

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An object in motion can change speeds many times as it moves from one point to another, speeding up or slowing down Average speed- total distance traveled divided by total time taken Constant speed- When an object covers equal distances in equal amounts of time. A race car travels at a constant speed of 96 m/s means for every second the car goes exactly 96 meters. Instantaneous speed- the rate at which an object is moving at a given instant in time.

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Speed The speedometer in a car measures the car’s instantaneous speed. Note the scale markings are given both in km/h and miles per hour, mph.

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Graphing motion You can show the motion of an object on a line graph in which you plot distance verses time. Slope- the steepness of a line on a graph Calculating slope (pg .23) Formula : Unit of measure:

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**The slope of a line on a distance-time graph is speed**

A steeper slope on a distance-time graph indicates a higher speed.

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Graphing Motion

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Graphing Motion

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Graphing Motion

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**Velocity- speed of an object AND its direction of motion**

Velocity is also a vector that shows changes in motion Vectors of varying lengths, each vector corresponding to the velocity at a particular instant, can represent motion. A longer vector represents a faster speed, and a shorter one a slower speed. Vectors point in different directions to represent direction at any moment

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Velocity A cheetah’s speed may be as fast as 90 km/h. To describe the cheetah’s velocity, you must also know the direction in which it is moving.

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Velocity As the sailboat’s direction changes, its velocity also changes, even if its speed stays the same.

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Assessment Questions A woman jogs 10 kilometers in one hour, stops at a restaurant for one hour, and then walks 10 kilometers in two hours. What is her average speed for the outing? 0.2 km/h 4 km/h 5 km/h 10 km/h

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Assessment Questions A woman jogs 10 kilometers in one hour, stops at a restaurant for one hour, and then walks 10 kilometers in two hours. What is her average speed for the outing? 0.2 km/h 4 km/h 5 km/h 10 km/h ANS: C

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Assessment Questions Lisa plotted time on the x-axis of a line graph and distance on the y-axis. What does the slope of her graph represent? total distance traveled velocity speed displacement

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Assessment Questions Lisa plotted time on the x-axis of a line graph and distance on the y-axis. What does the slope of her graph represent? total distance traveled velocity speed displacement ANS: C

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Assessment Questions Lisa plotted time in seconds on the x-axis of a line graph and distance in centimeters on the y-axis. Her plot showed a straight line from (0,0) to (10, 20). What is the speed? 0.5 cm/s 2 cm/s 10 cm/s 20 cm/s

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Assessment Questions Lisa plotted time in seconds on the x-axis of a line graph and distance in centimeters on the y-axis. Her plot showed a straight line from (0,0) to (10, 20). What is the speed? 0.5 cm/s 2 cm/s 10 cm/s 20 cm/s ANS: B

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**Two velocities of an object are combined by using**

Assessment Questions Two velocities of an object are combined by using division of the larger velocity by the smaller velocity. addition of the two speeds. vector addition. numeric addition.

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**Two velocities of an object are combined by using**

Assessment Questions Two velocities of an object are combined by using division of the larger velocity by the smaller velocity. addition of the two speeds. vector addition. numeric addition. ANS: C

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Assessment Questions The SI unit for speed of an airplane is miles per hour. True False

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Assessment Questions The SI unit for speed of an airplane is miles per hour. True False ANS: F, kilometers per hour

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