Static Friction: no surface motion. ch.5

Friction is dependent on FN --- Not on contact area Friction is dependent on FN --- Not on contact area ch.5

Kinetic & Rolling Friction: surface motion Sliding Block: ch.5

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A pickup truck accelerates smoothly and a box in back does not slide A pickup truck accelerates smoothly and a box in back does not slide. Is there surface motion as defined? Yes No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 ch.5

As defined, coefficients of friction are Dependent on normal force. Dependent on materials used. Dependent on both the above. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 ch.5

Block at rest. Draw a Force Diagram for the block. ch.5

Three boxes are pushed by force F with v > 0 along a horizontal surface with mk = 0.291. F=26N 3kg 5kg 2kg fk ch.5

Motion Along a Curved Path Motion Along a Curved Path ch.5

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Assume the car has m = 1200kg and ms = 0.92. Assume the car has m = 1200kg and ms = 0.92. At what speed would the car begin to slide? ch.5

Which force diagram applies to the object at Point D?

5-4 Numerical Integration: Euler’s Method Skip 5-4 Numerical Integration: Euler’s Method ch.5

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Both have same centripetal acceleration A disk rotates at a constant rate. Consider two points on the disk, one at radius R/2 and one at radius R. Which point has larger centripetal acceleration? Point at R/2 Point at R Both have same centripetal acceleration 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 ch.5

Is it possible for an object to have a non-zero acceleration when the velocity is constant? Yes No Cannot be determined 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 ch.5

Maximum angle block remains at rest: Derive the Angle of Repose relation: ch.5

Atwood with Friction: ch.5

Can you stop in time? Buggy rolls. You slide. ch.5

Insert values, determine ax. Given m = 75kg, M = 20kg, D = 3.5m, vo =1.1m/s. What frictional coefficient is needed? Insert values, determine ax. ch.5

Diagramming Refresher: ch.5

Stopping with 4W Disc-Brakes Accelerating with F2WD. Stopping with 4W Disc-Brakes ch.5

(60° is close to maximum angle) A 3kg box at rest on level surface with ms = 0.55. What is the largest F acting 60° below horizontal for which the box remains at rest? fs (60° is close to maximum angle) ch.5

Relative vs. Absolute Velocity vpc vpg P ch.5

Which force diagram applies to the object at Point B?

Which force diagram applies to the object at Point C?

Assume mass = 1. 2kg and radius = 45cm. If speed at Point D is 3 Assume mass = 1.2kg and radius = 45cm. If speed at Point D is 3.6m/s, what is the size of the normal force acting at Point D? -cen +cen ch.5

Q. Assume mass = 1. 2kg and radius = 45cm. If speed at Point B is 5 Q. Assume mass = 1.2kg and radius = 45cm. If speed at Point B is 5.1m/s, what is the size of the normal force acting at Point B? +cen -cen ch.5

Given: T = 50N, q = 30°, r = 1m Find: mg and v. Net ch.5

The speed is now 6.5m/s and r = 1.0m. Angle, tension, mass? Net For example, if m = 1.0kg, then T = 42.3N. ch.5

Q. The speed of a mass on a string of length L is 6. 5m/s Q. The speed of a mass on a string of length L is 6.5m/s. The radius r = 2.0m. Find angle, tension, mass, and L. Net For example, if m = 1.0kg, then T = 23.9N. ch.5

Practice Q: What is F such that 0 Practice Q: What is F such that 0.5kg block stays at rest if all surfaces are frictionless? ch.5

Banked Turn: ch.5

Banked Turn: ch.5

Modified Atwood Machine with friction. Objects are in CW motion. Let m1 = 2kg, m2 = 3kg, q = 30°, sliding friction coeff. 0.44 ch.5

Q. Recalculate last problem with m1 = 6kg m2 = 1kg Q. Recalculate last problem with m1 = 6kg m2 = 1kg. (All else remaining the same) ch.5

Practice Q: Find the variable relationships. ch.5

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Q. Assume the car has m = 1200kg and ms = 0.92. Q. Assume the car has m = 1200kg and ms = 0.92. How large is the frictional force if v = 15m/s? ch.5

5-3 Drag Forces ch.5

Drag Forces Can be approximated as, Fdrag = bvn Drag Forces Can be approximated as, Fdrag = bvn where b and n are constants ch.5

Example: Air drag, n = 2. If b = 25N/(m/s)2, at what speed would the object be resisted by 10N? At what speed would the same object be resisted by 30N? ch.5

Drag force grows quickly with v: Terminal Velocity: Reached when drag force equals weight force ch.5