 # Happyphysics.com Physics Lecture Resources Prof. Mineesh Gulati Head-Physics Wing Happy Model Hr. Sec. School, Udhampur, J&K Website: happyphysics.com.

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happyphysics.com Physics Lecture Resources Prof. Mineesh Gulati Head-Physics Wing Happy Model Hr. Sec. School, Udhampur, J&K Website: happyphysics.com

Ch 4 Newton’s Laws of Motion © 2005 Pearson Education

4.1 Force and interactions Force is a vector quantity Force is a vector quantity SI unit of force is Newton SI unit of force is Newton Pulling force Pushing force © 2005 Pearson Education

Typical Force Magnitudes © 2005 Pearson Education

Same effect as F © 2005 Pearson Education

Net Force © 2005 Pearson Education

4.2 Newton’s First Law A body acted on by no net force moves with constant velocity ( which may be zero) and zero acceleration A body acted on by no net force moves with constant velocity ( which may be zero) and zero acceleration F1 = F2 a = 0 In equilibrium © 2005 Pearson Education

Inertial Frames of Reference A frame of reference in which Newton’s first law is valid is called inertial frame of reference A frame of reference in which Newton’s first law is valid is called inertial frame of reference © 2005 Pearson Education

You and vehicle initially at rest You tend to remain at rest as the vehicle accelerates around you © 2005 Pearson Education

You and the vehicle are initially moving You tend to moving with constant velocity

4.3 Newton ’ s second Law Constant v Increasing v Decreasing v © 2005 Pearson Education

Acceleration is proportio n al to net force © 2005 Pearson Education

Newton’s second Law If a net external force acts on a body, the body accelerates. The direction of acceleration is the same as the direction of the net force. The net force vector is equal to the mass of the body times the acceleration of the body. If a net external force acts on a body, the body accelerates. The direction of acceleration is the same as the direction of the net force. The net force vector is equal to the mass of the body times the acceleration of the body. © 2005 Pearson Education

4.4 Mass and Weight © 2005 Pearson Education

Example 4.7 A 1.96x10 4 N Lincoln Town Car traveling in the +x-direction makes a fast stop; the x-component of the net force acting on it is -1.5x10 4 N. What is its acceleration? A 1.96x10 4 N Lincoln Town Car traveling in the +x-direction makes a fast stop; the x-component of the net force acting on it is -1.5x10 4 N. What is its acceleration? Ans: Ans: The mass of the car : The mass of the car : © 2005 Pearson Education

Newton’s Third Law If body A exerts a force on body B, then body B exerts a force on body A. These two forces have the same magnitude but are opposite in direction. These two forces act on different bodies. If body A exerts a force on body B, then body B exerts a force on body A. These two forces have the same magnitude but are opposite in direction. These two forces act on different bodies. © 2005 Pearson Education

Force diagrams © 2005 Pearson Education

Free body Diagrams mg N © 2005 Pearson Education

Summary

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