# Chapter 9 Notes.

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Chapter 9 Notes

Section 1 - Describing and Measuring Motion
Chapter 9

Section 1 - Motion An object is in motion if its distance from another object is changing. Earth moving at 30 km/sec Chapter 9

Section 1 - Reference point
A reference point is a place or object used for comparison to determine if something is in motion. Bus appears to move forward An object is in motion if it changes position relative to a reference point. Chapter 9

Section 1 - Standard Metric (SI) Base Units
International System of Units Système International d’Unités Length - meter Volume - liter Mass - gram prefixes - kilo = 1000 centi = 1/100 milli = 1/1000 Chapter 9

Section 2-Speed and Velocity
If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object To calculate the speed of an object, divide the distance the object travels by the amount of time it take to travel that distance. Speed = Distance/Time Units Chapter 9

Section 2-Speed and Velocity
Many objects do not move at a constant speed. To calculate the Average Speed, divide the total distance traveled by the total time. Example pg. 313 Chapter 9

Section 2-Speed and Velocity
Instantaneous speed is the rate at which an object is moving in a given instant in time. Chapter 9

Section 2-Speed and Velocity
When you know both the speed and direction of an object’s motion, you know the velocity of the object. Velocity = speed + direction 25 m/sec forward or 25 m/sec east Explore motion graphs - pg. 316 & 317 Chapter 9

Section 2-Speed and Velocity
Graphing Motion You can show the motion of an object on a line graph in which you plot distance versus time. Slope - steepness, or slant, of a line on a graph The faster the motion the steeper the slope slope = rise/run = y/x Chapter 9

Section 3 - Acceleration
Rate at which velocity changes In science, acceleration refers to increasing speed, decreasing speed, or change in direction. Increasing velocity - foot on gas Decreasing velocity - braking Change of direction = change in velocity (centripetal acceleration) Chapter 9

Section 3 - Acceleration
To determine the acceleration of an object moving in a straight line, you must calculate the change in speed per unit of time. Acceleration = (final velocity - initial velocity)/time Calculation example pg. 323 Chapter 9

Graphing Acceleration
You can use both a speed-versus-time graph and a distance-versus-time graph to analyze the motion of an accelerating object. Chapter 9

Graphing Acceleration
Speed vs. Time Graph Straight line = constant acceleration Curved line = changing acceleration Acceleration = slope Distance vs. Time Graph Straight line = constant speed Curved line = acceleration Speed = slope (Changing slope = acceleration) Chapter 9