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1-2 Notes – Speed, Velocity, Acceleration

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Rate A rate measures the change in one quantity in a particular length of time. –(e.g.) 2 meters per second –(e.g.) 5 revolutions per minute –(e.g.) 30 belches per minute

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Speed Speed is the rate of change of position over a period of time.

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Speed Speed, velocity, and acceleration describe how an object’s position and motion change through time.

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Speed An object that moves at a constant speed travels the same distance each and every second. This hurdler is moving at a constant speed of 5 m/s (Every second, she goes 5 m):

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Speed Instantaneous speed, or the speed of an object at a specific instant of time, is especially useful to measure for objects whose speed changes. A car driving in town must slow down and speed up, therefore its speed is not constant.

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Speed An object’s average speed is its total distance traveled divided by the total time it traveled.

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Speed The equation for average speed is: average speed = total distance total time total timeor v = d t

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Speed Use the triangle to solve word problems Cover up what’s missing & it tells you the math operation to use (multiply or divide)

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Speed 1. Genna biked 20 km. in 2 hr. What is her speed? 10 km/hr

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Speed 2. Jason ran at 5 m/s for 30 s. How far did he run? 150 m

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Speed 3. Geoff skated at 2 m/s for 200 m. How long did he skate for? 100 s

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Speed If you know any two quantities in the average speed equation, you can use the equation to calculate the third.

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Speed The unit for speed is a distance unit (meters) divided by a time unit (seconds). The SI unit for speed is m/s.

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Velocity Velocity is a measurement of both the speed and direction of motion of an object.

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Velocity Velocity is a vector. It has both a size (the speed of the object) and a direction (the direction the object is moving). The velocity vector of a ball changes when the direction and speed of the ball change. Where is its speed increasing?

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Velocity Speed is different from velocity because speed does not include the direction in which the object is moving.

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Acceleration Acceleration, another vector, is the rate at which velocity changes over time. m/ss

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Acceleration When an object speeds up or slows down, its velocity changes, meaning that it is accelerating.

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Acceleration When an object speeds up, the direction of its acceleration is the same as the direction of its motion.

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Acceleration When an object slows down, its acceleration is in the opposite direction from the direction of its motion.

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Acceleration When an object changes the direction in which it is moving, its velocity changes. This means that it is accelerating. The horses on the carousel are constantly accelerating and changing direction, so they are constantly changing velocity even though their speed remains constant.

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Discuss: Is it possible to accelerate while standing still on the ground?

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Discuss: Yes! It all depends on your point of reference. Even if you are standing still with respect to the ground beneath you, you are moving because Earth itself is moving. It rotates around its axis, and revolves around the Sun.

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Acceleration is the rate of change of ____. Avelocity Bspeed Ctime Ddirection 1.2 Speed, Velocity, and Acceleration

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A car stopping at a red light is an example of a(n) ____. Adisplacement Bacceleration Cdirection Dvelocity 1.2 Speed, Velocity, and Acceleration

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It takes a runner 50 s to run a distance of 150 m. What is the runner’s average speed? A0.3 m/s B3 m/s C100 m/s D50 m/s 1.2 Speed, Velocity, and Acceleration

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A runner traveling at 5 m/s will cover what distance in 3 min? A900 m B90 m C9 m Dnone of the above

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If a car travels 10 km in 5 min, stops for 2 min, and then travels 4 km in 3 min, what is the average speed of the car? A14 km/h B14 km/min C1.4 km/min D1.4 km/h

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Cars on an oval race track are accelerating because ____. Athey are changing direction Btheir displacement is zero Call of the above Dnone of the above

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If an object increases its speed, then it is ____. Achanging velocity Bchanging direction Cchanging the reference direction Dnone of the above

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Which of the following is the rate of change in distance divided by time? Avector Bdisplacement Cinstantaneous speed Daverage speed SCI 1.b

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If a car travels 45 km in half an hour, what is the average speed of the car? A45 km/h B45 km/min C90 km/h D90 m/s SCI 1.c

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Velocity has both ____ and ____. Asize; magnitude Bsize; speed Cspeed; direction Ddirection; origin SCI 1.d

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What occurs when an object accelerates? AIt speeds up. BIt slows down. CIt changes direction. Dall of the above SCI 1.e

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