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Chapter 4 - Motion

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Frames of Reference Is this train in motion? How do you know?

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Frames of Reference Frames of reference help us to describe the motion of something

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Frames of Reference RELATIVE MOTION is movement in relation to a frame of reference.

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Frames of Reference Frame of Reference ObjectRelative Motion You – on a moving bus Your friend – in a nearby seat You – on a moving bus Your friend – standing at the bus stop You – standing at the bus stop Your friend – on the moving bus

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Measuring Distance Distance is the length between 2 points When measuring the length, be sure to include units (cm, km, m)

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Measuring Displacement Displacement is direction + length between starting and ending points

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Displacement Along a Straight Line A VECTOR is a quantity the describes size, length or amount, and direction – Same direction = add them – Opposite directions = subtract the difference – Example: Figure 4.2 on page 78

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Displacement That Isn’t Along a Straight Path Use graphing to help determine displacement Displacement is always shorter than or equal to the distance

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QUICK LAB!!! Using graph paper and rulers, draw a path on your paper with at least 3 turns. Measure the total distance of the path and displacement.

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Review! What’s a frame of reference? What’s is distance? How is displacement different than distance?

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4.1 Vocabulary Speed Average speed Instantaneous speed velocity

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Speed SPEED is the ratio between the distance an object travels to the amount of time is takes Example: 50 miles/hour

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Average Speed vs. Instantaneous Speed Average speed = total distance/total time – Formula: s = d/t Instantaneous Speed = how fast something is moving at any given movement – Example: a speedometer in a car measures instantaneous speed

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Graphing Motion The slope of a line on a distance-time graph is speed The steeper the slope, the faster the speed! Check out page 83-84 for comparing graphs!

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Velocity Speed in a given direction! Velocities in the same direction are added Velocities in opposite directions are subtracted

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4.3 Vocabulary Acceleration Free fall Constant acceleration Linear graph Nonlinear graph

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What is acceleration?? Acceleration = rate at which velocity changes Can be described as a change in speed, change in direction, or change in both The rate of acceleration, due to gravity is 9.8m/s/s

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Changes in Speed FREE FALL – movement of an object toward Earth solely because of gravity

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Changes In Direction You can accelerate even if your speed is constant! Example: the speed may be constant on a carousel, but the direction is always changing

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Changes in Speed and Direction Sometimes speed and direction can change at the same time Example: riding a roller coaster!

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Constant Acceleration A steady change in velocity The velocity of the object changes by the same amount each second

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Calculating Acceleration Acceleration = change in velocity/total time – Formula = (v f – v i ) t Complete the Math Practice problems on page 346

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Graphs of Accelerated Motion The slope of a speed-time graph is acceleration Check out pages 86 & 89 for graphing examples!

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