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Define the term motion. Give an example of something in motion. How do we know an object is in motion? How do we know if we are in motion even if our eyes are closed?

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SPS8 Students will determine relationships among force, mass, and motion. a. Calculate velocity and acceleration.

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What is needed to describe motion completely? How are distance and displacement different? How do you add displacements?

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How do we know an object is moving? Frame of reference Motion is always relative (compared to) something That something is called the Frame of Reference for us usually the earth)

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How do we know an object is moving? Frame of reference We choose a frame that makes sense. Using the ground as a frame, the ball is moving forward Using the truck as a frame of reference, the ball goes up then back down

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Distance – the length of a path between two points Displacement – straight line distance (and direction) between the start and end Example: Travel 3.5 miles south

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PHET Vector Addition PHET Vector Addition Adding Displacements (vector addition) Vector – has number value and direction If the vectors aren’t in a straight line, then we have to use trigonometry to add the vectors

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How are instantaneous speed and average speed different? How can you find the speed from a distance-time graph? How are speed and velocity different? How do velocities add?

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SR-71 Blackbird Speed: 2070 mph or 920 m/s Speed – ratio of distance to time Measured in meters per second (m/s) Average Speed Example: A car travels 25 km in 0.2 hours, then 45 km in 0.3 hours. What is the average speed? Total distance and then total distance

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Practice: A person jog 400 meters in 192 seconds, then 200 meters in 132 seconds, and finally 100 meters in 96 seconds. What is the joggers speed?

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Practice: A train travels 190 kilometers in 3.0 hours, and then 120 kilometers in 2.0 hours. What is its average speed?

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A speedometer does not measure average speed, it measures instantaneous speed.

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A distance time graph can be used to determine speed. The slope of the graph (distance divided by time) is average speed Gizmo Distance vs. Time

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Velocity – speed in a direction (vector) Velocity changes with either A change in speed A change in direction Velocity is added by vector addition (like displacement)

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How are changes in velocity described? How can you calculate acceleration? How does a speed-time graph indicate acceleration? What is instantaneous acceleration?

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Acceleration is a change in velocity, so Change in speed ▪ Either getting faster ▪ Or getting slower Change in direction ▪ Turning Measured in meters per second squared (m/s 2 )

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Calculating Acceleration – divide the change in velocity (speed) by the total time Example: A ball rolls down a ramp, starting from rest. 4 seconds later, it’s velocity is 13 m/s. What is the acceleration of the ball? First, what is the initial velocity? 0 m/s

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Practice Problem 1 A car traveling at 10 m/s slows down to 3 m/s in 20 seconds. What is the acceleration?

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Practice Problem 2 An airplane travels down a runway for 4.0 seconds with an acceleration of 9.0 m/s 2. What is its change in velocity during this time?

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Reading a Speed-Time graph The slope of the graph (rise over run) is the acceleration Straight upward – positive constant acceleration Straight downward – negative constant acceleration (slowing down) Flat – constant speed, no acceleration Curved – changing acceleration

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How does gravity cause acceleration?

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Free Fall – when an object is falling under only the influence of gravity The acceleration due to gravity on the surface of the earth is 9.80 m/s 2 So our acceleration equation becomes Everything else is the same

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Problem 1 How fast will a rock dropped from the top of the empire state building be going after 8.0 seconds?

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