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Chapt . 11

Chapt . 11. Motion. Motion. Problem: Is your desk moving?? What would you say? Someone on the moon? Someone on the sun? How about outside our own galaxy? We need a reference point - nonmoving point from which motion is measured

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Chapt . 11

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  1. Chapt. 11 Motion

  2. Motion • Problem: • Is your desk moving?? • What would you say? Someone on the moon? Someone on the sun? How about outside our own galaxy? • We need a reference point - nonmoving point from which motion is measured • Motion is the change in position in relation to a reference point

  3. Distance & Displacement • Distance: length of a path between 2 points • Usually calculated in meters - “walk 5 blocks from the bus stop” • Displacement: the direction from the starting point and the length of a straight line from the starting point to the ending point (change in position) -”walk 5 blocks north from the bus stop” -vector quantity: has direction & magnitude

  4. Distance vs. Displacement Problem: What would be the displacement of a rollercoaster one time around its track?

  5. Vectors • A vector is a quantity that has both magnitude and direction. It is represented by an arrow. The length of the vector represents the magnitude and the arrow indicates the direction of the vector. Blue and orange vectors have same magnitude but different direction. Blue and purple vectors have same magnitude and direction so they are equal. Blue and greenvectors have same direction but different magnitude. Two vectors are equal if they have the same direction and magnitude (length).

  6. Combining Vectors • When motion is in a straight line, vectors add and subtract easily 2 km 4 km 4 km + 2 km = 6 km 2 km 4 km – 2 km = 2 km 4 km

  7. Displacement that isn’t along a straight path (p. 331) School Resultant vector 3 Distance? 7 blocks 2 Displacement? 5 blocks 1 Home 1

  8. Speed • Distance an object travels over the amount of time it takes to travel • Usually measured in meters/sec (m/s) • Speed can be expressed in 2 ways: • Average speed : entire duration of trip • Instantaneous speed : measured at a particular instant

  9. Average Speed • During the time an object is moving, its speed may change, but this equation allows you to calculated average speed over entire trip • Practice: While traveling on vacation you measure the times and distances traveled. You travel 35 km in 0.4 hr, followed by 53 km in 0.6 hr. What is your average speed?

  10. Instantaneous Speed • Sometime, such as driving on a highway, you need to know how fast you are going at a particular moment

  11. Graphing Motion

  12. Velocity • The speed and direction in which an object is moving • Velocity is a vector quantity • Can change even when speed is constant • Velocity vectors can be added by vector addition: 5 km/hr Resultant vector 12 km/hr 13 km/hr

  13. Summary • What does velocity describe? • What shows the speed on a distance-time graph? • What is the difference between average speed and instantaneous speed? • How can 2 or more velocities be combined?

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