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Chapter 2

Chapter 2. Newton’s First Law. 2.1 Aristotle’s Classification. Motion requires push or pull (4 th century BC) Aristotle- two kinds of motion

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Chapter 2

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  1. Chapter 2 Newton’s First Law

  2. 2.1 Aristotle’s Classification • Motion requires push or pull (4th century BC) • Aristotle- two kinds of motion • Natural- on Earth, directed up or down, like boulders falling or smoke rising, objects have resting places that they naturally seek, does not need force • Unnatural motion- requires forces from people or animals (cart moving across ground)

  3. 2.2 Galileo • Aristotle’s ideas were fact for 2000 years • Galileo disproved that heavy things fall faster than light things (from same time @ leaning tower of Pisa) • Force required to start motion, but not required to keep it going (except to overcome friction) • Rolled balls on incline, horizontal plane • Incline = increase speed, horizontal = forever

  4. Inertia • Inertia- object in motion stays in motion, object at rest stays at rest • More mass = more inertia (resists change) • Theoretically could go on forever without something to stop the rolling • What would stop the rolling?

  5. 2.3 Speed and Velocity • Before Galileo, slow and fast only. How could these choices help us today? Hurt us? • Galileo came up with speed as distance covered in a length of time (distance/time) • Examples on board

  6. Velocity • Velocity = speed with a direction • The addition of a direction makes it a vector • Constant speed = no speed change • Constant velocity also means no direction change (not going in a circle) • Not constant motion leads to acceleration

  7. 2.4 Motion is Relative • You’re in constant motion, even when completely still • You are going 100,000 km/hr relative to the sun • Most often, use Earth as a reference point (otherwise, wouldn’t know if we’re going fast or slow)

  8. 2.5 Newton • Newton • Falling apple • Cofounder of Calculus • Extended Galileo’s work on inertia, creating laws • 3 laws of motion • First law- object in motion stays in motion, at rest stays at rest unless acted upon by another force • Second law = F = ma (Chapter 3) • Third law = law of action and reaction ( Chapter 4)

  9. First Law • Simply, objects keep on doing what they’re doing until they are made not to • Examples • Pull tablecloth out from under dishes, no broken dishes • Coin drops into glass after resting on card on mouth of glass • Can swing water over your head in a circle and not get wet (Steve Spangler)

  10. 2.6 Net force • Combination of all forces on an object = net • Net = overall, total, etc. • I pull with 5 newtons, you pull in same direction with 5 newtons, net = 10 newtons (remember, vectors) • If in opposite direction, subtract • Problems on board

  11. 2.7 Equilibrium for Resting Objects • Equilibrium means equal, or cancel out • No net force • ΣF = 0 • Σ means sigma, or sum (see Microsoft Excel) • All pluses and minuses cancel • Problems on board

  12. 2.8 Support Force • Why don’t we go through the floor? • Support force/ normal force (at a right angle) makes net force zero • We push down, floor pushes up

  13. 2.9 Equilibrium for moving objects • Equilibrium still means equal, so net force is still zero • Not resting, but no change (graph on board) • Forces oppose moving object • Usually this is friction • Static equilibrium = at rest • Dynamic equilibrium = constant velocity

  14. 2.10 Earth moves around sun • Remember Galileo proved Copernicus’ theory • People thought bird would not be able to swoop down and catch worm if planet moved • But we’re all moving! • We’re used to faster paces, such as …

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