Balancedvsunbalancedforces 3 physical science 1

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Unformatted text preview: External forces cause motion, internal forces do not. · A net force is the resultant of several forces acting in the same or different directions. Balanced forces are those that result in a net force of zero. Unbalanced forces are those that result in a net force greater than zero. Balanced vs. Unbalanced Forces 3 Physical Science 1 Chapter 3 N 2 D LAW OF MOTION The Force Law · The acceleration of a body is directly proportional to the net force acting on the body, and inversely proportional to the mass of the body, and in the direction of the net force. Net Force Acceleration= Mass F a= net or Fnet = ma m The relationship between Force, Mass and Acceleration 4 Physical Science 1 Chapter 3 N 2 D LAW OF MOTION Examples: 1. What constant net force will give 2.0­kg object an acceleration of 5.0 m/s2 ? F = ma =(2.0 kg)(5.0 m/s2 ) = 10 N 2. A net force of 90 N acts on a 60­kg ice skater. What is the acceleration? 3. A force of 100 N is applied to a box with a mass of 20­kg, to move it across a floor. If the friction between the box and the floor is 20 N, what is the acceleration of the box? 100 ¾ ¾ ¾ N ¾ ¾® Net force = Acceleration = 5 20 kg 20 ¬¾N¾ ¾ Physical Science 1 Chapter 3 WEIGHT & MASS · Weight of an object is the effect of gravity on the mass of the object, and is direct result of Newton’s 2nd Law. w eight = mass x gravity - - - F = m x a Examples: 1. Calculate the weight of a 70.0­kg person on earth and on the moon, where gravity is 1/6 of the earth. Earth w = mg = (70.0 kg)(10 m/s 2 )=700 N Moon w = mg = (70.0 kg)( 10 )m/s 2 )=117 N 6 2. A jar weighs 5.0 N. What is its mass? 3. An 80.0­kg persons weights 765­N on top of a mountain. Calculate the acceleration due to gravity on the mountain. g = w 765 N 2 = = 9.56 m/s m 80.0 kg 6 P...
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