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Ch 9 – Day 2

Ch 9 – Day 2. March 17 & 18 . ω = 2 / T ω = 2 / (10s) = ~0.628 RPS. v t = ω r OR = (2 / T v t = (0.628 RPS) 3m v t = ~1.884 m/s. ω = 2 / T ω = 2 / ( 8 s)  CAREFUL !!! = ~0.785 RPM. v t = ω r OR = (2 / T v t = ( 0.785 RPM) 3m

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Ch 9 – Day 2

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  1. Ch 9 – Day 2 March 17 & 18

  2. ω = 2 / T ω = 2 / (10s) = ~0.628 RPS vt =ωrOR = (2 / T vt=(0.628 RPS) 3m vt =~1.884 m/s

  3. ω = 2 / T ω = 2 / (8s)  CAREFUL!!! = ~0.785 RPM vt =ωrOR = (2 / T vt=(0.785 RPM) 3m vt =~2.355 m/s

  4. See definitions. (spin vs. orbit, etc.) Revolves – the axis is EXTERNAL of the kid Linear/Tangential: circumference per time Rotational/Angular: # of spins per time Etc.

  5. 4. Tangential (speed, velocity, etc.) 5. As rotational speed increases, so does tangential speed… DIRECTLY PROPORTIONAL! 6. As RADIUSincreases, so does tangential DIRECTLY PROPORTIONAL! 7. larger diameter = larger tangential speed

  6. In Summary… No Yes Yes • Newton’s 1st Law states that if there is NO net force, • an object at rest will stay at rest • An object in motion will stay in motion without acceleration • In other words, it will not accelerate  it will not change its velocity  it will not speed up, slow down, or change direction. • Does the marble travel in a straight line? • So…does it change direction? • So… does it change velocity?

  7. In Summary… No Yes Yes Yes • Newton’s 2nd Law states that IF there is a net force, • an object will accelerate • In other words it will change its velocity  it will speed up, slow down, change direction or any combination of the 3. • Does the marble travel in a straight line? • So…does it change direction? • So… does it accelerate? • So… is there a force that causes this acceleration? Your goal is to figure out what direction this force acts (and therefore, what direction the acceleration acts, since the acceleration is in the same direction as the net force)

  8. In Summary… No Yes Yes Yes • Newton’s 2nd Law states that IF there is a net force, • an object will accelerate • In other words it will change its velocity  it will speed up, slow down, change direction or any combination of the 3. • Does the marble travel in a straight line? • So…does it change direction? • So… does it accelerate? • So… is there a force that causes this acceleration? Your goal is to figure out what direction this force acts (and therefore, what direction the acceleration acts, since the acceleration is in the same direction as the net force)

  9. Centripetal Force • Means “center seeking” or “towards the center” • Any force that causes an object to follow a circular path. • EXAMPLE: The force that holds the occupants in a rotating ride. • Name give to any force that is directed at a right angle to the path of a moving object and that tends to produce circular motion • If the centripetal force is removed, an object will follow a straight line, TANGENTIAL path (like in the plate & marble, and hula hoop demo!)

  10. Centrifugal Force • Means “center fleeing,” or “away from the center” • The Physics F-WORD!!!! F is for fake, false, fabricated, fictitious, forbidden, etc… • Very commonly misused. • (people say centrifugal when they should say centripetal) • It is NOT real force because it is NOT part of an action-reaction pair! • Misconception that centrifugal force pulls you outward during circular motion. THERE IS NO FORCE PULLING YOU OUTWARD! • Actually, it is just the inertia of the body traveling tangent to the circle.

  11. As a ball is whirled above the head, it is the inertia of the ball that wants to continue moving in a straight line. Instead, the ball is forced inward to change its direction (Centripetal Force-supplied by string). • Inward Force • Inward acceleration • Tangent velocity

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