phy2048-ch5_new

# phy2048-ch5_new - 1 Chapter 5 – Force and Motion II I...

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Unformatted text preview: 1 Chapter 5 – Force and Motion II I. Drag forces and terminal speed. II. Uniform circular motion. III. Non-Uniform circular motion. I. Drag force and terminal speed-Fluid: anything that can flow. Example : gas, liquid.-Drag force: D- Appears when there is a relative velocity between a fluid and a body.- Opposes the relative motion of a body in a fluid. - Points in the direction in which the fluid flows. Assumptions : * Fluid = air. * Body is blunt (baseball). * Fast relative motion b turbulent air. 2 ) 3 . 6 ( 2 1 2 Av C D ρ = ) 4 . 6 ( 2 A C F v g t ρ =-Terminal speed: v t 2 1 2 =- → = → =- g g F Av C a if ma F D ρ C = drag coefficient (0.4-1). ρ = air density (mass/volume). A= effective body’s cross sectional area b area perpendicular to v- Reached when the acceleration of an object that experiences a vertical movement through the air becomes zero b F g =D II. Uniform circular motion-Centripetal acceleration: ) 6 . 6 ( 2 R v m F = ) 5 . 6 ( 2 r v a = A centripetal force accelerates a body by changing the direction of the body’s velocity without changing its speed. v, a = ctes, but direction changes during motion.-Centripetal force: a, F are directed toward the center of curvature of the particle’s path. 3 III. Non-Uniform circular motion 2 2 t r a a a + =- A particle moves with varying speed in a circular path.- The acceleration has two components: - Radial b a r = v 2 /R- Tangential b a t = dv/dt- a t causes the change in the speed of the particle.- In uniform circular motion, v = constant b a t = 0 b a = a r r r v dt v d a a a r t ˆ ˆ 2- = + = θ a a a a ∑ ∑ ∑ + = t r F F F a a a 49. A puck of mass m slides on a frictionless table while attached to a hanging cylinder of mass M by a cord through a hole in the table. What speed keeps the cylinder at rest? Mg mg T T N = → = → c a Mg T M For 33E. Calculate the drag force on a missile 53cm in diameter cruising with a speed of 250m/s at low altitude, where the density of air is 1.2kg/m 3 ....
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phy2048-ch5_new - 1 Chapter 5 – Force and Motion II I...

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