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Chapter 3: LINEAR MOTION

Chapter 3: LINEAR MOTION. Motion Is Relative. Motion of objects is always described as relative to something else. For example:. You walk on the road relative to Earth, but Earth is moving relative to the Sun.

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Chapter 3: LINEAR MOTION

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  1. Chapter 3: LINEAR MOTION

  2. Motion Is Relative Motion of objects is always described as relative to something else. For example: • You walk on the road relative to Earth, but Earth is moving relative to the Sun. • So your motion relative to the Sun is different from your motion relative to Earth.

  3. Speed • Defined as the distance covered per amount of travel time (meters per second). • In equation form: Example: A girl runs 4 meters in 2 sec. Her speed is 2 m/s.

  4. Average Speed • The entire distance covered divided by the total travel time • Doesn’t indicate various instantaneous speeds along the way. • In equation form: Example: Drive a distance of 200 km in 2 h and your average speed is 100 km/h.

  5. Instantaneous Speed Instantaneous speed is the speed at any instant. Example: • When you ride in your car, you may speed up and slow down. • Your instantaneous speed is given by your speedometer.

  6. Velocity • A description of • the instantaneous speed of the object • what direction the object is moving • Velocity is a vector quantity. It has • magnitude: instantaneous speed • direction: direction of object’s motion • Average velocity = (initial vel + final vel )/ 2

  7. Speed and Velocity • Constant speed is steady speed, neither speeding up nor slowing down. • Constant velocity is • constant speed and • constant direction (straight-line path with no acceleration).

  8. Acceleration Formulated by Galileo based on his experiments with inclined planes. Rate at which velocitychanges over time

  9. Acceleration Involves a • change in speed, or • change in direction, or • both. Example: Car making a turn

  10. Acceleration In equation form: Unit of acceleration is m/s2. or Final velocity – Initial velocity= Acceleration x time

  11. An automobile is accelerating when it is slowing down to a stop. rounding a curve at a steady speed. Both of the above. Neither of the above. Acceleration CHECK YOUR NEIGHBOR

  12. An automobile is accelerating when it is slowing down to a stop. rounding a curve at a steady speed. Both of the above. Neither of the above. Acceleration CHECK YOUR ANSWER Explanation: • Change in speed (increase or decrease) is acceleration, so slowing is acceleration. • Change in direction is acceleration (even if speed stays the same), so rounding a curve is acceleration.

  13. Kinematic equations of motion: • Vf = V0 +at • Vf2 = V02 + 2aD • D = V0t+0.5at2 • Note: • valid only if acceleration is constant. • If the object is in free fall; acceleration = g = 9.8 m/s2 • Note: The above equations will be provided during the test.

  14. Free Fall Falling under the influence of gravity only - with no air resistance • Freely falling objects on Earth accelerate at the rate of 9.8 m/s2.

  15. Free Fall—How Fast? The velocity acquired by an object starting from rest is So, under free fall, when acceleration is 10 m/s2, the speed is • 10 m/s after 1 s. • 20 m/s after 2 s. • 30 m/s after 3 s. And so on.

  16. Free Fall—How Far? The distance covered by an accelerating object starting from rest is So, under free fall, when acceleration is 10 m/s2, the distance is • 5 m/s after 1 s. • 20 m/s after 2 s. • 45 m/s after 3 s. And so on.

  17. The following are short problems which should give you ample exercise to get comfortable with problem solving. Also you can use these as a study guide for the test. • Problem solving book: 10c, 11b, 16b & c, 24b &c, 26b &c. We will try to solve these (as many as possible) in class. • If you are comfortable with the above, try the following at home: 38, 39, 42, 43, 45, 46, 51,55.(Most of these problems are very similar.)

  18. Conceptual Physics textbook: • Pg 46 – 7, 8, 10 • Pg 47 – 18, 21, 23 • Pg 49 – 5, 8, 17, 20, 27, 38, 40

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