Chapter 4: Basic of Forces | California State University, Northridge

University:
California State University, Northridge
Course:
PHYS 100A | General Physics I
Academic year:

2023
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KOLEJ MATRIKULASI SELANGOR physics\academic\1PN 2 Forces 4.1 Basic of Forces Weight, W: the force exerted on a body under gravitational field, W = mg Tension, T: the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends Normal, N/ Reaction, R: a reaction force that exerted by the surface to an object interact with it Friction, f: a force that resists the motion of one surface relative to another with which it is in contact Free body diagram: A diagram that shows the sizes and direction of all forces acting upon an object 4.2 Newton’s Laws of Motion 1st Law: An object at rest will remain at rest, or continues to move with uniform velocity in a straight line unless it is acted upon by an external forces Fnett = 0 Forces are balanced Objects at REST (v = 0 m s-1) a = 0 m s-1 Stay at rest 2nd Law the rate of change of linear momentum of a moving body is proportional to the resultant force and is in the same direction as the force acting on it 𝑑𝑝 F 𝑑𝑡 𝑑𝑝 𝐹 , 𝑝 = 𝑚𝑣 𝑑𝑡 𝑑(𝑚𝑣) 𝐹= 𝑑𝑡 𝑑𝑣 𝑑𝑣 𝑣−𝑢 𝐹 = 𝑚( ),( ) = ( ) 𝑑𝑡 𝑑𝑡 𝑡 𝑣−𝑢 𝑣−𝑢 𝐹=( ),( )=𝑎 𝑡 𝑡 F = ma Forces are unbalanced Fnett  0 There is an acceleration (a ≠ 0 m s-2) - The acceleration depends directly upon the nett FORCE The acceleration depends inversely upon the object's MASS Object in MOTION (v ≠ 0 m s-1) a = 0 m s-1 Stay in motion (same speed & direction) 3rd Law every action force has a reaction force that is equal in magnitude but opposite in direction FAB = – FBA