PHY 101 1st Edition Lecture 9Outline of Last LectureI. Projectile MotionII. Velocity ComponentsIII. DisplacementIV. Direction of Velocity Outline of Current Lecture V. Why do things move?VI. Aristotle vs. NewtonVII. 4.1 ForcesVIII. 4.2 Newton’s First LawCurrent Lecture- Why and how do things move?o Relationship between motion of object’s and forces acting on them = dynamicso Concepts: Force, mass acceleration, action & reactiono Laws: Newton’s three laws Newton’s law of universal gravitation- Aristotle vs. Newtono Aristotle: first theory of motion (wrong theory) Everything is in a state of rest until you give it a push “force is the cause of motion” Makes sense but is wrong – widely accepted until 17th centuryo Newton Force is NOT a cause of motion but it causes CHANGE in motion (acceleration) What are forces?- 4.1 Forceso Ex. Push/pull Contact forces: you need physical contact to apply forceo Ex. Gravitational, magnetic, and electricThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Field forces: don’t need direct physical contacto A force is a vector SI Unit: Newton (N)o Can be contact or field force Contact forces result from physical contact between objects Field forces occur between disconnected objectso Only field forces are fundamental At a microscopic level, contact force is also field forceo 4 fundamental forces in nature (strongest to weakest) Strong nuclear force (subatomic particles) Electromagnetic force (between charges, magnets) Weak nuclear force (radioactive decay) Gravitational force (between masses)- 4.2 Newton’s First Lawo First law of motion: “An object move with a velocity that is constant in magnitude and direction, unless acted on by a nonzero net force.”o Before the 17th century, people believed the natural state of matter was at resto Galileo: the natural state of matter is to continue its original state of motiono Newton formalized Galileo’s idea into the first law of motiono “things tend to stay where they are”o If an object is at rest, it will stay at rest until an external force is applied on ito If an object is moving, it will keep on moving at a constant velocity until an external force is applied on ito Mass: a measure of the resistance of an object to changes in its motion due to forceo Net Force: The vector sum of all the external forces exerted on the objecto External Force: Any force that results from an interaction with an object and it’s environmento Internal Force: Forces that originate within the object itself They cannot change the object’s velocity **you cannot pull yourself
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