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Motion of an object Average Speed Velocity Acceleration

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Objects move in relation to a reference point. Reference point The tree is the reference point since it stays in place.

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When an object changes position over time relative to a reference point, the object is in motion. When the motorcycle changes position over time relative to the tree, the motorcycle is in motion.

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You can describe the direction of the object’s motion with the reference direction… North, south, east, west, up, or down.

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The speed of an object is the distance traveled by an object divided by the time taken to travel that distance. S = distance/time (S = d/t)

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If the motorcycle traveled 10 meters and it took it 2 seconds, how fast is the motorcycle traveling? S = d/t S = 10 meters/ 2 seconds S = 5 m/s Don’t forget units!

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Think to yourself about how you walk class to class….is it at a constant pace? Most often, objects do not travel at a constant speed, so we need to calculate the average speed. Average speed = total distance/total time

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Mr. Summers swims a distance from one end of a 50 m pool to the other end in a time of 25 s. What is Mr. Summer’s average speed? S = d/t S = 50 m/ 25 s S = 2 m/s

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Distance (m)Time (s) Create a graph of this data. Label your y-axis as “distance” and your x- axis as “time”.

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Since the graph is comparing distance to time, then the line represents SPEED! S = d/t Distance (m) Time (s) Speed of object

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Picture two birds leaving a tree at the same time. They both fly at 10 km/h for 5 min. Why don’ they end up at the same place? They went in different directions!

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The speed of an object in a particular direction is called velocity. The speeds of the birds were the same, but they had different velocities.

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Which is the correct way to describe the velocity of a car traveling on I-5? “A car’s velocity is 60 m/h” “A car’s velocity is 60 m/h south.”

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Picture sitting in a car at a stop light, when it turns green what happens to the car? “Speeding up” is commonly described by using the word acceleration. However, in science it means much more…

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Acceleration is the rate at which velocity changes over time….. So velocity changes when speed changes, direction changes, or both.

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A car accelerates when it increases it’s speed from 25 to 35 m/h. A car accelerates when it turns a corner. A car accelerates when it puts it’s brakes on for a stop sign.

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Positive acceleration – increase in velocity. Negative acceleration – decrease in velocity (also called deceleration) List two examples of each in your compbook. Share with your neighbor.

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Acceleration is also how fast velocity changes. … The faster the velocity changes, the faster the acceleration.

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Since acceleration is the rate at which velocity changes over time….. Acceleration = final velocity – starting velocity time it takes to change velocity A = V f – V i t

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Mrs. Rhoades is riding her bike south downhill. At the top of the hill she is going 1 m/s south and at the bottom she is going 5 m/s south. It took her 4 sec to go travel the entire hill. What was Mrs. Rhoades acceleration down the hill? A = V f – V i t A = 5 m/s – 1 m/s = 1 m/s/s South 4 s

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A plane passes over point A at a velocity of 240 m/s north. 40 seconds later, it passes point B at a velocity of 260 m/s north. What is the plane's average acceleration? A = V f – V i t A = 260 m/s – 240 m/s = 0.5 m/s/s north 40 s

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Create a graph of this data. Label your y-axis as “Velocity” and your x- axis as “time”. Velocity (m/s)Time (s)

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Since the graph is comparing velocity to time, then the line represents acceleration! A = V f – V i t Velocity (m/s) Time (s) Acceleration of object

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Think about a person spinning around on their feet… are they accelerating? Yes! An object traveling in a circular motion is always changing its direction, therefore always changing velocity. So its accelerating!

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The acceleration that occurs in a circular motion is called centripetal acceleration! Centripetal acceleration happens on a Ferris wheel or as the moon orbits the earth.

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