Force and Motion Physics 2053 Lecture Notes Laws of Motion (Chapter 4) 2053.ppt

Forces Types Range Size 100 Gravitational Unlimited 106 1020 1035 Gravitational Unlimited Electromagnetic Unlimited Weak Nuclear  10-12 m Strong Nuclear  10-15 m Laws of Motion (Chapter 4) 2053.ppt

If no external force acts, an object maintains a constant velocity. Newton’s First Law (Law of Inertia) If no external force acts, an object maintains a constant velocity. Laws of Motion (Chapter 4) 2053.ppt

Mass Gravitational mass mg Inertial mass mi mg = mi Laws of Motion (Chapter 4) 2053.ppt

Newton’s Second Law Units of Force System Mass Acceleration Force SI kg m/s2 N = kg m/s2 British slug ft/s2 lb = slug ft/s2 Laws of Motion (Chapter 4) 2053.ppt

m Force of Gravity and Weight Weight = mg Laws of Motion (Chapter 4) 2053.ppt

Action/Reaction Forces Force block exerts downward on table top Newton’s Third Law F1 Force table exerts upward on block F2 Action/Reaction Forces Laws of Motion (Chapter 4) 2053.ppt

Applications of Newton’s Laws Find Tensions T1 and T2 q T1 sin(60) T1 cos(60) T1 T2 mg m q = 60o m = 20 kg Laws of Motion (Chapter 4) 2053.ppt

Applications of Newton’s Laws Another method q mg T1 T2 T2 mg m Laws of Motion (Chapter 4) 2053.ppt

Applications of Newton’s Laws vo= 0 Dt = 5 s m = 5 kg F v = ? m Find velocity of block after Dt Laws of Motion (Chapter 4) 2053.ppt

Applications of Newton’s Laws vo= 20 m/s m = 5 kg v = 0 F m d Find distance block moves Laws of Motion (Chapter 4) 2053.ppt

Forces on m1 N T m1 T m1g m2 m2g Forces on m2 Laws of Motion (Chapter 4) 2053.ppt

Mass 1 Mass 2 T T m2 m2g m1 m1g Laws of Motion (Chapter 4) 2053.ppt

y x q mg Frictionless incline N mg sin(q) mg cos(q) q Laws of Motion (Chapter 4) 2053.ppt

m1 T T m2 m2g sin(q2) m1g sin(q1) m2g m1g q1 q2 Laws of Motion (Chapter 4) 2053.ppt

Friction: m mg Force of Static Friction N F fs Laws of Motion (Chapter 4) 2053.ppt

Friction: v Force of Kinetic Friction N F fk m mg Laws of Motion (Chapter 4) 2053.ppt

Table 5.2 Coefficients Of Friction Steel on steel 0.74 0.57 Aluminum on steel 0.61 0.47 Copper on steel 0.53 0.36 Rubber on concrete 1.0 0.8 Wood on wood 0.25-0.5 0.2 Glass on glass 0.94 0.4 Waxed wood on wet snow 0.14 0.1 Waxed wood on dry snow ------ 0.04 Metal on metal (lubricated) 0.15 0.06 Ice on ice 0.1 0.03 Teflon on Teflon 0.04 0.04 Laws of Motion (Chapter 4) 2053.ppt

y N fk q x q mg a mg sin(q) mg cos(q) Acceleration on a rough incline Laws of Motion (Chapter 4) 2053.ppt

Rough surface N T fk m1g T m2g Laws of Motion (Chapter 4) 2053.ppt

F m 2m 3m Three mass system - find acceleration Find the tensions in the string. First find the acceleration of the system. Laws of Motion (Chapter 4) 2053.ppt

T2 F m 2m 3m Three mass system - find T2 Laws of Motion (Chapter 4) 2053.ppt

T1 T2 F m 2m 3m Three mass system - find T1 Laws of Motion (Chapter 4) 2053.ppt

x y N q F N f mk F q f m mg mg Pulling a block Pulling a block with constant speed x y N q F N f mk F q f m mg mg The normal force A man drags a 20 kg crate at constant speed across a floor by pulling on a rope inclined at 35 degrees above the horizontal. The tension in the rope is 40 N. Find the magnitude of the a) normal force exerted on the crate by the floor. b) frictional force acting on the crate. c) coefficient of kinetic friction between the crate and floor. Laws of Motion (Chapter 4) 2053.ppt

y N F N mk F q f q m f x mg mg Pulling a block with constant speed The frictional force A man drags a 20 kg crate at constant speed across a floor by pulling on a rope inclined at 35 degrees above the horizontal. The tension in the rope is 40 N. Find the magnitude of the a) normal force exerted on the crate by the floor. b) frictional force acting on the crate. c) coefficient of kinetic friction between the crate and floor. Laws of Motion (Chapter 4) 2053.ppt

N y F N mk F q f q m f x mg mg Pulling a block with constant speed The coefficient of friction A man drags a 20 kg crate at constant speed across a floor by pulling on a rope inclined at 35 degrees above the horizontal. The tension in the rope is 40 N. Find the magnitude of the a) normal force exerted on the crate by the floor. b) frictional force acting on the crate. c) coefficient of kinetic friction between the crate and floor. Laws of Motion (Chapter 4) 2053.ppt

m = 200 kg vo= 20 m/s ms = 0.500 Truck’s maximum deceleration Crate on truck ms = 0.500 Truck’s maximum deceleration A flatbed truck traveling at 20 m/s is carrying a 200 kg crate of heavy machinery. The coefficient of static friction between the crate and the bed of the truck is 0.500. The driver applies the brakes and brings the truck to rest as quickly as possible without the crate sliding Find the a) magnitude of the trucks acceleration when coming to a stop? b) time of the acceleration? c) distance traveled during the acceleration? Laws of Motion (Chapter 4) 2053.ppt

A block is released from rest at the top of an incline. Frictionless A block is released from rest at the top of an incline. Find the final speed and the time to side to the bottom. N d q mg mg sinq mg cosq q Laws of Motion (Chapter 4) 2053.ppt

A block is released from rest at the top of an incline. With friction f = mkN = mkmg cosq A block is released from rest at the top of an incline. Find the final speed and the time to side to the bottom. N f d q mg mg sinq mg cosq q Laws of Motion (Chapter 4) 2053.ppt

Force and Motion END Laws of Motion (Chapter 4) 2053.ppt