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Classical Mechanics Lecture 4

Classical Mechanics Lecture 4. Today's Concepts: Newton’s Laws a) Acceleration is caused by forces b) Force changes momentum c) Forces always come in pairs d) Good reference frames. First Midterm Exam on Friday. Covers Units 1-3 plus “Math” One-dimensional Kinematics

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Classical Mechanics Lecture 4

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  1. Classical Mechanics Lecture 4

    Today's Concepts: Newton’s Laws a) Acceleration is caused by forces b) Force changes momentum c) Forces always come in pairs d) Good reference frames
  2. First Midterm Exam on Friday Covers Units 1-3 plus “Math” One-dimensional Kinematics Two-Dimensional Kinematics Relative and Circular Motion Unit conversion Trigonometry and Algebra 50 minute duration Multiple choice Review on Wednesday Unit 4 will resume on Monday
  3. Sir Isaac Newton and his 3 Laws
  4. Main Points
  5. Main Points
  6. Main Points
  7. Lecture Thoughts
  8. Let’s start with Newton’s 2nd Law
  9. Newton’s 2nd Law Acceleration is caused by force. A bigger mass makes this harder
  10. Force is a Vector Quantity Force is a vector. Acceleration vector is parallel to (same direction) as (Net) force vector.
  11. Newton’s 2nd Law Acceleration is caused by force. A bigger mass makes this harder
  12. Pre-lecture Question 1
  13. Pre-lecture Question 1
  14. Unit of Force Kinematics units Dynamics unit
  15. Momentum
  16. Spaceship example
  17. Newton’s First law
  18. Inertial Reference Frame
  19. Newton’s 3rd Law
  20. Newton’s 3rd Law The motion of an object is affected by only the forces acting upon it.
  21. Prelecture Question 2
  22. Prelecture Question 2
  23. Checkpoint 1 The net force on a box is in the positive x direction. Which of the following statements best describes the motion of the box : A) Its velocity is parallel to the x axis B) Its acceleration parallel to the x axis C) Both its velocity and its acceleration are parallel to the x axis D) Neither its velocity or its acceleration need be parallel to the x axis
  24. CheckPoint The net force on a box is in the positive x direction. Which of the following statements best describes the motion of the box : A) Its velocity is parallel to the x axis B)Its acceleration parallel to the x axis C) Both its velocity and its acceleration are parallel to the x axis D) Neither its velocity or its acceleration need be parallel to the x axis B) Net force causes acceleration, but it does not necessarily say anything about the direction of the velocity.
  25. Force on Two Masses A force F is applied to a small block, that pushes a larger block. The two blocks accelerate to the right. Compare the NET FORCE on the block with mass M, to the net force on the block with mass 5M. A)FM < F5M B)FM = F5M C)FM > F5M a 5M F M
  26. Force on Two Masses Net Force A force F is applied to a small block, that pushes a larger block. The two blocks accelerate to the right. Compare the NET FORCE on the block with mass M, to the net force on the block with mass 5M. A)FM < F5M B)FM = F5M C)FM > F5M Same acceleration, so larger mass has larger net force. a 5M F M
  27. Checkpoint You are driving a car with constant speed around a horizontal circular track. The net force acting on your car A) Points radially inward toward the center of the circular track B) Points radially outward, away from the center of the circular track C) Points forward in the same direction your car is moving D) Points backward, opposite to the direction your car is moving E) Is zero.
  28. CheckPoint
  29. Aside: Centripetal acceleration and force 1) Objects moving in a circle always have a component of acceleration, called centripetal, which is toward the center of the circle.* 2) Centripetal acceleration must be caused by a force: Friction, gravity – whatever force keeps it moving in a circle. This force is often called the “centripetal force” 3) There is no “new” kind of force here. 4) There is no such thing as centrifugal force. * They can have also have tangential acceleration if their speed is not constant
  30. Momentum & Force
  31. Checkpoint Momementum You are driving a car with constant speed around a horizontal circular track. The momentum of your car
  32. Momentum & Centripetal Acceleration
  33. Momentum & Centripetal Acceleration
  34. Newton’s 1st Law Ice-puck Fake Forces: Coriolis (YouTube)
  35. Hurricane Earl And makes hurricanes rotate CCW (CW) in the Northern (Southern) hemisphere. This effect can make cannons miss their targetif you don’t takeit into account. Physics 211 Lecture 4, Slide 41
  36. Newton’s 3rd Law Forces come in pairs! Fire-cart
  37. Clicker Question A small guy and a large football player moving at the same speed collide head-on. Which person experiences the larger force during the collision? A) The small guy. B) The football player. C) They experience the same force.
  38. Main Points
  39. Main Points
  40. Main Points
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