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Published byDamon Horace Montgomery Modified over 6 years ago

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Chapter 3 Linear Motion

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5.DESCRIPTION OF MOTION Speed Velocity Acceleration

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Speed Average Speed = distance/time Units - m/s, ft/s, etc. Instantaneous Speed is the speed you would read from a speedometer

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Distance vs. Time graph Time Distance Instantaneous Speed is the slope of this graph at a point

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Average Velocity Time Distance Find end-points Connect with a line Find slope of the line

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Choose Different End-Points Time Distance Find end-points Connect with a line Find slope of the line

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Example of Average Speed You take a trip from A to B and back to A. You want to average 60 mph for the round trip A to B to A. A B 2 miles From A to B you average 30 mph. What is your average speed on the return trip from B to A? 30 mph

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Velocity Average Velocity = Displacement/time Units - m/s, ft/s, etc. Instantaneous Velocity of an object is its instantaneous speed plus the direction it is traveling Velocity is a vector.

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Displacement and Average Velocity Distance traveled is the length of the path taken. Average velocity =

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Acceleration Acceleration = "change" in velocity/time Units - m/s 2, ft/s 2, etc. Acceleration is also a vector Velocity Time Acceleration is the slope of a Velocity vs. Time graph.

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Motion at constant velocity Accelerated motion HereHere, too

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Demo - Ball on incline and ball on table Deceleration = negative acceleration

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Acceleration on Galileo's Inclined Planes (equal time slices)

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Velocity and Acceleration Galileo used inclined planes to study accelerations. He found constant accelerations for inclines. (It was too hard to measure time for free-falls.) He also found that the mass of the objects didn't matter.

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Relationships Between v and a for Linear Motion If initial velocity is zero, then

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Example A jogger starts at zero velocity with an acceleration of 3 ft/s 2. How fast is she moving after 4 seconds?

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6.FREE FALL Motion near the surface of the earth in the absence of air resistance. The acceleration of an object is g = 32 ft/s 2 = 9.8 m/s 2

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How Fast Velocity in gravitational field (starting from rest) v = gt = 32t English Or v = 10t Metric

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Distance Equation d o = initial distance v o = initial velocity g = acceleration due to gravity

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Free Fall Falling in a gravitational field: Take d o and v o to be zero (object starts from the origin at rest) Then: d = d o + v o t + ½at 2 becomes d = ½gt 2 d = 5t 2 (Metric)

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Free Fall Time of Fall (s) Velocity Acquired (m/s) – 10t Distance Fallen (m) – 5t 2 1 2 3 4 5 10 20 30 50 40 125 80 45 20 5

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Demonstrations Demo - Reaction timer Demo - Paper and book drop

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Free Fall Graphs Ball released from rest, down positive, measure distance from point of release.

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Different Assumptions Ball thrown up from origin with an initial speed of 10 m/s, up is positive

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Free Fall - How Quickly How Fast Acceleration Is How Quickly - How Fast - Changes in Velocity Acceleration is difficult to understand because it is a rate of a rate.

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