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# Conservation of Angular Momentum, Change in Angular Momentum and, Angular Impulse

Conservation of Angular Momentum, Change in Angular Momentum and, Angular Impulse. October. Conservation of Angular Momentum. L mom is a conserved quantity/remains constant in the absence of an external force (i.e. torque)

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## Conservation of Angular Momentum, Change in Angular Momentum and, Angular Impulse

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1. Conservation of Angular Momentum, Change in Angular Momentum and, Angular Impulse October

2. Conservation of Angular Momentum • Lmom is a conserved quantity/remains constant in the absence of an external force (i.e. torque) • Since Lmom is a constant for an isolated system, and because the Lmom formula can be rearranged to give v = Lmom /(mr), the velocity v and the separation r are inversely correlated. • thus, conservation of angular momentum demands that a decrease in the separation r be accompanied by an increase in the velocity v, and vice versa. • We observed this during our Ironman demo: mrBIGvsmall = mrsmallvBIG Another example

3. Change in Angular Momentum • How do we deal with a change in angular momentum (∆ Lmomor∆ Iω)? • The same way we did with a change in linear momentum • Recall, for linear momentum: Change in linear momentum = ∆P= m∆v • Same for change in angular momentum except symbols change: Change in Angular momentum = ∆Lmom= I ∆ ω where ∆ ω = ω2- ω1 • Let’s try Example 2 part “a” from pg.56

4. Angular Impulse • Recall from linear impulse that J=F∆t which means that a linear impulse is the result of a force applied in a certain amount of time ex. Hydraulic spreader (HUGE jaw force applied to outer edges of car door for 1min results in HUGE IMPULSE to pry open door) • Angular Impulse is what causes objects to start or stop rotating • Like linear impulse it still happens in a certain amount of time EXCEPT, since rotation, the force required to start that rotation is called TORQUE • TORQUE is a force applied from a certain distance from the center of object such that; Torque(T) = Fxd where F(N or lb), d (m or ft), T (N.m or lb.ft)

5. Working with Angular Impulse • Angular Impulse causes rotation when torque (F x d) is applied to an object in a certain period of time. • Screw begins to turn due to angular impulse applied from wrench Ang.Imp. = (Fxd)∆t where Ang.Imp. has units (N.m).s or (lb.ft).s • we could re-write equation as Ang.Imp.= T∆t • And of course don’t forget: Impulse (in this case angular impulse) is what causes change in momentum so: • Let’s try part “b” of Example 2 pg.56 T∆t = I∆ω

6. Classwork/Homework (whatever is not finished in class must be finished for hmwk) • Read pg.44-50 • Complete Qd-g from Let’s Review units on pg.55 • Complete Student Exercises(#1-11) on pg.51. You must write out the full question for Q1-10 and use GFS for #11. • Answer Qs #4-6 on pg.57 of workbook

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