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Glencoe Chapter 3

Glencoe Chapter 3. Describing Motion. Who Wins?????. Racer with the fastest speed? Racer with the shortest elapsed time? What is motion? What is speed? How is speed different from velocity?. Battery Buggy.

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Glencoe Chapter 3

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  1. Glencoe Chapter 3 Describing Motion

  2. Who Wins????? • Racer with the fastest speed? • Racer with the shortest elapsed time? • What is motion? • What is speed? • How is speed different from velocity?

  3. Battery Buggy • After watching the buggy, how is it’s motion different/similar to a 100 meter sprinter? What if the batteries were close to dead?

  4. Motion is Relative • Perception of motion by humans is always related to nearby objects. • Even if there is motion, but no nearby reference, motion is not perceived by humans.

  5. 3.1 Picturing Motion • When an object moves, it’s position changes. • A MOTION DIAGRAM is a tool that may be used to study the motion of an object.

  6. How do you know the answer is correct?

  7. Motion Diagrams—you draw! What kind of motion does the diagram depict?

  8. Operational Definition • An Operational Definition defines a concept in terms of the procedure or operation used. • Examples • Rest? Object does not change position with relation to a reference point. • Constant speed? Object travels equal distances in equal time periods. • Acceleration? • Deceleration

  9. What’s Happening here?

  10. Or here?

  11. Particle Model • These types of Diagrams are a little difficult to draw. Maybe we can substitute something else for little pictures of the moving object…

  12. A ticker-tape timer

  13. Ticker Tape: "slower" acceleration Ticker Tape: "Faster" acceleration Ticker Tape: "faster" deceleration Ticker Tape: "slower" deceleration

  14. Ticker-tape Math Speed = distance time From timer device rate Time Taken = 5 X .025s = 0.125 s

  15. Now you try it…. • Page 46 of your text, #1-4

  16. 3.2 Where and When? • Coordinate Systems—Tell where zero point of variable you are studying is and the direction in which the value of the variable increases. • Origin—Point at which values for variable are zero.

  17. X-Y Coordinate System • Motion of many types may be shown on a coordinate system, for example • a ball thrown upward • A cannon firing a cannonball • a high diver diving off a board • A high jumper • We can use an x-y system, • X is horizontal movement • Y is vertical movement

  18. We can define upward as positive, which is standard. • We can define to the right as positive • However, you can choose any direction as either positive or negative, just make sure the opposite direction has an opposite sign.

  19. Symbols in Physics Symbols are frequently used to represent quantities in Physics m represents mass SI unit kg t represents time s s represents speed m/s d represents distance m a represents acceleration m/s2 v represents velocity m/s Δd represents displacement m

  20. Vectors and Scalars • Another way of representing the position of an object would be to use a vector. Vectors or scalars are used to represent quantities in physics. • A scalar is a line segment, whose length represents only magnitude • Time is a scalar quantity • A Time interval is the difference between two time periods i.e 2 hours interval between 2:00 and 4:00 • Mass is a scalar quantity, along with others

  21. Vectors • A vector is a ray whose length represents magnitude, and the ray points in the direction. • Vectors are used to represent quantities that have both magnitude as well as direction. • Displacement is a vector quantity • Is the distance and direction between two positions

  22. Examples • Speed……….. • Velocity……... • Acceleration.. • Time…………. • Distance……. • Force……… Scalar quantity Vector quantity Vector scalar scalar vector

  23. Vector Quantities • Vector quantities are represented with arrows over the symbol. • Velocity • acceleration

  24. Examples • Equation for acceleration

  25. A position vector drawn from origin to position of object y d0 x

  26. Position Vectors

  27. Another Position vector

  28. Velocity Vectors

  29. Displacement vs. Position • Position is the position where an object is located. • Indicated as “d”, or sometimes d0, d1 • Displacement is the change in position of an object between two time periods. • Indicated as “Δd” • Found by subtracting, d1-d0 • Δd = d1-d0

  30. Time Interval • Time intervals (Δt) are defined as the time between two time periods. Δt = t1-t0

  31. Displacement vectors drawn between positions at two different time periodsDisplacement (Δd) is equal to difference between two position vectors (d1-d0) Δd = d1-d0 Velocity vectors drawn for each time period, length indicates magnitude (speed)

  32. You drive the path, and your odometer goes up by 8 miles (your distance). Your displacement is the shorter directed distance from start to stop (purple arrow). What if you drove in a circle? Distance vs. Displacement start stop

  33. 3.3 Velocity and Acceleration • Motion diagrams can be used to show objects moving with different speeds and different kinds of motion. • Motion diagrams can show position and time, but can we combine them to determine a rate of motion?

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