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Displacement & velocity

Displacement & velocity. Divisions of classical physics. Kinematics: the study of motion w/o regard to cause. Have you ever seen the root word “kine” before? Where? Dynamics: the study of the forces which cause & change motion.

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Displacement & velocity

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  1. Displacement & velocity

  2. Divisions of classical physics • Kinematics: the study of motion w/o regard to cause. Have you ever seen the root word “kine” before? Where? • Dynamics: the study of the forces which cause & change motion. • We are going to begin our study of classical physics with a study of kinematics

  3. distance & displacement • distance – scalar (d) • displacement – vector (d) • Distance is the magnitude of displacement. • Dimensions of d (or d) = length m (MKS) or cm (CGS).

  4. speed & velocity • Dimensions of t (time)? MKS? CGS? • Dimensions of v or (v)? MKS? CGS? • By dimensional analysis – what must be the formula for d? • d = vt or d = vt

  5. What is the relationship b/w the direction of d and the direction of v? • How do you know?

  6. Given the formula, d = vt, derive the formula for velocity. • d = vt  d/t = vt/t  v = d/t • Now check the formula to see if it is dimensionally correct. • m/sec = m/sec

  7. Simplest motion • The simplest type of motion: motion with constant speed in a straight line. • Does constant v always have constant v? • Give an example when an object with constant speed does not have constant velocity.

  8. Principle of Relativity • All motion is relative. The velocity of an object depends on the “frame of reference” from which one observes the event. • Frame of reference: where you view an event. Point of view.

  9. What is the horizontal velocity of a ball throw straight up on a bus if the bus is traveling 50 mi./hr. E? • Vbe or Vbb? Which is correct? • What is your velocity right now? • Motion w/ constant velocity (constant mag. & dir.) cannot be proven. • Ex. Car @ a stoplight. • If one were in an airplane that is moving w/ constant velocity it would be impossible from inside the airplane to prove whether the plane or the earth is moving!

  10. Playing catch in a train

  11. Determining relative velocity • Vector addition or subtraction. You must learn which. This is not to be confused w/ + or – direction.

  12. Subscript system • Velocity of what – 1st subscript • Relative to what – 2nd subscript • second subscript same subtract • If 2nd subscripts are different -> add

  13. Sample relative velocity problem • A train is moving E @ 60 km/hr., a waiter is walking twd the rear of the train @ 2 km/hr., and a fly is crawling across the waiters tray @ 3 km/hr N. What is the velocity of the fly relative to earth? vfe vfw Vector diagram vwt vte

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