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Ch. 5: Newton’s Laws of Motion DYNAMICS

Ch. 5: Newton’s Laws of Motion DYNAMICS. Concept of Force. Force : “A push or a pull”. F is a VECTOR ! Need vector addition to add forces!. Vector addition to add Forces!. Examples of Forces. “Pushing” forces. “Contact” forces. “Pulling” forces. “Field” forces (Physics II).

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Ch. 5: Newton’s Laws of Motion DYNAMICS

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  1. Ch. 5: Newton’s Laws of Motion DYNAMICS

  2. Concept of Force • Force: “A push or a pull”. F is a VECTOR! • Need vector addition to add forces! Vector addition to add Forces!

  3. Examples of Forces “Pushing” forces “Contact” forces “Pulling” forces “Field” forces (Physics II)

  4. Measurement of Forces:Spring Scale Vector addition to add Forces! 

  5. Newton’s Laws of Motion A common MISCONCEPTION in the 21st Century! • The ancient (&wrong!) view (of Artistotle): • Need a force to keep an object in motion. • The “natural” state of an object is at rest. • CORRECT VIEW(of Galileo & Newton): • It’s just as natural for an object to be in motion at constant speed in a straight line as to be at rest. • At first, imagine the case of NO FRICTION • Experiment:If NO FORCE is appliedto an object moving at a constant speed in straight line,it will continuemovingat the same speed in a straight line! If I succeed in having you overcome the wrong ancient misconception & understand the correct view of this, A MAJOR GOAL of the COURSE WILL HAVE BEEN ACHIEVED! Proven by Galileo in the 1620’s! 

  6. Reference Frames • Inertial Reference Frame (As defined by Newton) ≡A reference frame(coordinate system)which is moving with constant velocity (no acceleration!) with respect to the “fixed stars”. • Clearly, an idealization! Rigorously, Newton’s Laws are ONLY valid in an Inertial Reference Frame

  7. Newton’s Laws • Galileo laid the ground work for Newton’s Laws. • Newton: Built on Galileo’s work • Newton’s 3 Laws:One at a time Galileo Galilei  in middle age  Sir Isaac Newton as a young man

  8. Newton’s First Law • 1st Law:(“Law of Inertia”): “In the absence of external forces and when viewed from an inertial reference frame, an object at rest remains at rest and an object in motion remains in motion with a constant velocity (constant speed in a straight line).” Newton was born the same year Galileo died! Sir Isaac Newton as an older man

  9. Newton’s 1st Law:(Alternate Language): 1. “When no net force (∑F = 0) acts on an object, the acceleration of the object is zero.” ∑ = a math symbol meaning sum (capital sigma) 2. “If an object does not interact with other objects, it is always possible to identify a reference frame (an inertial frame) in which the object has zero acceleration.” • From 1st Law:Can define aForceas “An action which causes a change in the motion of an object.”

  10. Newton’s 1st Law: First stated by Galileo!

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