FACULTY OF SCIENCE, AUTUMN 2006
PHYS 124 LEC A1 : Particles and Waves
(Instructor: Marc de Montigny)
Walker, Physics, Chapter 9: Linear Momentum and Collisions
- Section 9-1: Linear Momentum
- P. 241, Eq. 9-1 (Definition of Linear Momentum): p = mv
- SI Units: kg⋅m/s
- P. 242, Eq. 9-2 (Total momentum vector of a system of objects):
ptotal = p1 + p2 +
p3 + ...
- Read P. 242, Example 9-1
- Section 9-2: Momentum and Newton's Second Law
- P. 244, Eq. 9-3 (Newton's Second Law): ∑ F = Δp/Δt
- P. 244 connects this equation to the usual form of Newton's 2nd Law.
- This form will allow us to state the principle of conservation of momentum.
- Section 9-3: Impulse
- P. 244, Eq. 9-5 (Definition of Impulse): I = FavΔt,
where Fav is the average net force acting on the object.
- P. 245, see Figure 9-2. Fav is such that
the area under the rectangle is equal to the sum under the curve.
- P. 245, Eq. 9-6 (Momentum-Impulse Theorem):
I = FavΔt = Δp
- P. 275, Problem 14
- Section 9-4: Conservation of Linear Momentum
- P. 248, Eq. 9-7: Δp = pf - pi =
∑ FΔt, follows from Eq. 9-3.
When the net force is zero,
∑ F = 0, this gives pf =
pi, P. 248, Eq. 9-8.
- Read P. 249: Internal Versus External Forces
- P. 250, Eq. 9-9 : Δpnet =
(∑ Fext) Δt
- P. 275, Problem 21
- P. 278, Problem 60
- Sections 9-5 and 9-6: Collisions
- In a collision, the momentum p of a system is conserved:
pf = pi
- Different types of collisions:
- P. 253 (Inelastic Collisions): Kinetic energy is not conserved, i.e.
Kf ≠ Ki.
- P. 253 (Completely Inelastic Collisions): When the objects stick together
after the collision.
- P. 259 (Elastic Collisions): Kinetic energy is conserved, i.e.
Kf = Ki.
- P. 279, Problem 75
- P. 276, Problem 35
- Section 9-7: Centre of Mass
- P. 265, Eq. 9-14/15 (Centre of Mass of N objects):
XCM = (∑ mx)/∑ m
YCM = (∑ my)/∑ m
- The Centre of Mass of a finite object is essentially the
average position of this object, weighted by the mass of its
constituents.
- P. 277, Problem 42
- P. 279, Problem 73
- P. 280, Problem 82
- P. 279, Problem 76 (May be solved by using the
"Trick of Negative Mass")
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