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Chapter 2 Notes

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**Scientific models Used to solve complex questions 3 types**

Physical model- Something you can physically manipulate The car and ramp are examples Conceptual model- Descriptive models usually describing how something works Copernicus describing how planets revolve around sun Graphical model Shows relationship between 2 variables

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Graphical models Can use graphs to predict values that you did not measure Ex. Predicting speed in lab 2.1

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**Types of relationships**

Strong positive relationship Strong inverse relationship Weak relationship No relationship

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Position vs. distance Position: where something is compared to where it started including direction- as things move, position changes Distance: interval of length without regard to direction- you could walk in a circle and your position would be the same, but you would have traveled a distance Ex: You walk 7km north away from school, then walk back to the school- What is your position? What is your distance traveled?

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**Position vs. Time Graph The slope of this graph is speed at**

any given time and position

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**Finding slope in general**

Choose two points on a graph Pt 1 (0.5, 30) Pt 2 (1.5, 60) Use the following formula: The units show you that the slope you found is speed

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**Average vs. Instantaneous speed**

Average speed- speed that results from whole journey Total distance/time Instantaneous speed- speed at a particular point on the journey Position/ time

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**Acceleration Rate of change in speed of an object**

Formula: Change in speed/change in time Units: cm/ sec2

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**Acceleration Occurs when Deceleration- decrease in speed over time**

You speed up You slow down You change direction Deceleration- decrease in speed over time 0 acceleration- traveling at a constant rate or stopped

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An example

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**Free Fall Acceleration due to gravity: 9.8m/s2**

This means that for every second an object falls, its speed increases by a factor of 9.8m/s Ignore air resistance

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**Speed vs time graph Find slope- the units you get are cm/sec2**

In other words, slope of a speed vs time graph is acceleration

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