Lecture 03 Dynamics Forces and Motion Along A Line

Dynamics: Forces and Motion Along A Line

Force ( ) - a vector quantity that basically affects the motion of the object - commonly defined as “push” or “pull” Units of Force: SI Unit: newton (N) Gaussian: dyne English: pound (lb) Net Force ( ) - resultant force or sum of all forces acting on the object.

Net force Physicists who contributed to the development of force and motion relationship: Aristotle (384-322 BC) Galileo (2000 years later, approx. 1678) Isaac Newton (1687) - Principia (book published) - “three laws of motion”

Newton’s First Law Law of Inertia:An object at rest or an object in motion at constant velocity will remain at rest or at constant velocity in the absence of a net force. ,[object Object]

The body moves at constant velocity. ,[object Object]

mass (m) - is a measure of inertia of a body. - synonymous to quantity of matter. This means that it is constant! * The more mass a body has, the harder it is to change its state of motion.

Newton’s Second Law: Law of Acceleration:Whenever a net force acts on an object, it produces an acceleration with a direction the same to the direction of the net force - an acceleration that is directly proportional to the net force and inversely proportional to the mass. Unit Conversion: 1 N = 1 kg m/s2; 1 dyne = 1 g cm/s2 1 lb = 1 slug ft/s2

Pushing the cart with twice the force produces twice the acceleration. Three times the force triples the acceleration. Acceleration and Force With Zero Friction Forces

F F a/2 a Pushing two carts with same force F produces one-half the acceleration. The acceleration varies inversely with the amount of material (the mass). Acceleration and Mass Again With Zero Friction

Newton’s Third Law Force of Man on Floor Force of Ceiling on Man Force of Wall on Hands Force of Floor on Man Force of Hands on Wall Force of Man on Ceiling Law of Interaction:Toevery action force there must be an equal and opposite reaction force. Action and reaction forces act on different objects.

Action Reaction Action Reaction Newton’s Third Law Two More Examples: Action and Reaction Forces Act on Different Objects. They Do Not Cancel Each Other!

Weight, Normal Force, and Tension Weight (w) – gravitational force w = mg where m = mass of the object g = acceleration due to gravity ,[object Object]

Weight is not constant while mass is!,[object Object]

Normal force (FN) - contact force that acts perpendicular to the common surface of contact. FN T w w Tension (T ) - force of a string, cable, wire running on the body

Lecture 03 Dynamics Forces and Motion Along A Line

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Lecture 03 Dynamics Forces and Motion Along A Line