1Chapter 2Newton’s First Law of Motion –Inertia22Aristotle• Four elements:– Earth, water, air and fire• Natural motion– Any motion in which an element “strives” to be with the same element– Quintessence – celestial spheres; perfect and unchanging•Violent motion– Any motion where an outside force acts on an elementEarth falls to earth – the more earth, the faster it will fall (heavier objects fall faster).Smoke rises into the air.Give the feather example (this will be a lead in for the Apollo moon experiment).I got a little bit ahead of myself on this slide and covered all of the information on the next slide (geocentric universe).33Aristotle’s Universe• Aristotle said that the “heavens” did not obey the same laws as the Earth because the Earth was corrupted• Spheres where regarded as perfect and the most perfect motion was circular motion• Therefore, the Earth was the center of the universe with the heavens revolving around it in perfect circles– This is called the geocentric universeI showed this slide even though I covered all of this information on the last slide since it is nice to see the information in writing to get good notes.44The Geocentric UniverseNotice the order of the planets moving out from the Earth and that all of the stars are on the last sphere.55Copernicus’ Universe• For nearly 1800 years, Aristotle’s conception of the universe stood as fact, until..• In the early 16thcentury, Nicolaus Copernicus developed a view on the universe with the Earth revolving around the sun– This is called a heliocentric universe• Copernicus received a copy of his book on the day he diedExplain why Copernicus was hesitant on publishing his heliocentric ideas and the potential repercussions.66Galileo “Weighs” In•In the late 17thcentury, Galileo discredited Aristotle’s concept of motion by proving that all objects, no matter their weight, fall at the same rate• Discrediting Aristotle opened the door to give credit to Copernicus’ heliocentric universe• Galileo encountered great resistanceTalk about how Galileo was placed under house arrest by the church and his book was banned for 200 years, but today, even the Catholic church accepts his theories and apologized for his treatment.At the end of this slide, ask why, if everything falls at the same rate, does a feather fall slower than a hammer (this is a lead into the Apollo moon experiment).77Apollo 15This is the movie of the Apollo 15 hammer and feather drop – and yes, both hit the surface of the moon at the same time.88Galileo’s Inclined Planes• Galileo used inclined planes to prove that, no matter what the shape of the inclined plane, the ball always climbed back to the same height• This is an example of inertiaAfter explaining the first two illustrations, ask what would happen if there was no second inclined plane (this is a nice lead into the 1stlaw).99Newton’s First LawInertia:• “Every object continues in its state of rest, or uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it”• In other words: objects at rest stay at rest and objects in motion stay in motionHere would be a good place to give an in-class demonstration showing inertia -> Pull a sheet out from under a book.1010Net Force and Equilibrium• Force – any push or pull on an object; a force has both magnitude and direction• Equilibrium – a state of no change• When object are in equilibrium, the net force is zero• Two forces can add to zero net force by canceling directionsMake an example where the net force yields no motion and then an example of when the motion has constant velocity.1111Net Force IllustrationsThis is a slide that illustrates how forces can net out to zero.Add chalk board illustration on how to add forces.Perhaps this would be a good point for a more detailed discussion of vectors.1212Support Force• While you are sitting in your chair, you are exerting a force with your body on the chair• Support (normal) force is the force the chair needs to apply to you to bring you into equilibrium• Equilibrium can be also be achieved when something is moving in a straight line with constant speed– Example, a hockey puck moving over the iceNote that a bathroom scale works by measuring how much force the scale needs to apply to you to support your weight.Note that an object under the influence of only one force can NEVER be in equilibrium.By this the “Equilibrium of Moving Things” section will be covered.1313The Moving Earth• The Earth moves around the sun at more than 18 miles/second• Why then do we feel at rest?• Why does a dropped ball fall directly to the ground and not fly away as the Earth moves under it?Make sure to ask the answers from the students before moving onto the next slide with the answers.1414And the Answer is…• Inertia tells us that once something is in motion, it tends to stay in motion– To be at rest on the Earth, we must be moving with it• We do not feel this motion because it is so constant that we are essentially in equilibrium• The ball falls directly to the ground because it is moving at the same speed of the EarthWe are not undergoing any appreciable acceleration so we feel like we are at rest.After this slide, invite the students to try the tablecloth pull themselves and ask them to try to fail at it. Ask them to explain how both succeeding and failing are examples of