Chapter 2. Newton's First Law of Motion: Inertia

Transcription

1 Chapter 2 Newton's First Law of Motion: Inertia 2.1 Aristotle on Motion natural motion up/down/circular violent motion pushing or pulling forces proceeds from the nature of an object 1

2 proceeds from the nature of an object Aristotle said: "all motions are due to the nature of the moving objects or due to a sustained push or pull. If an object is in its proper place it will not move unless subjected to a force" sounds good, but incorrect!!!! 2

3 Chpt 2 notes.notebook Copernicus suggest the theory of a moving earth copernicus/ the earth circles the Sun in circular orbits heliocentric not popular with church leaders 2.2 Galileo's Experiments Aristotle said "heavier objects fall faster" Galileo showed that all object fall at the same rate!!!! 3

4 Inclined planes Galileo studied "how" things moved, not "why" if there is no interference a moving object will move in a straight line forever push or pull we call this property of wanting to move in a straight line continually inertia inertia is a resistance to a change in motion it is a tendency of a objects that are moving or at rest!!! 4

5 headrest football slideplayer.com mass is a measure of an objects inertia when it's at rest mass and velocity is measure of an objects inertia when it's moving! mass is a basic unit of measure of the amount of matter in an object 5

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8 Mass is measured by a pan balance! mass = force/acceleration force = mass x acceleration acceleration = force/mass m = f/a f = ma a = f/m 8

9 Force: push or pull gravity electrical magnetic nuclear Net Force: when more than one force acts! algebraic sum! 9

10 Net Force: when more than one force acts! algebraic sum! 2 1 C 2 60 N C 1 70 N Net Force: when more than one force acts! algebraic sum! c 2 head to tail method 1) draw vectors to scale c

11 Net Force: when more than one force acts! algebraic sum! c 2 head to tail method 1) draw vectors to scale 2) place the tail of the 2nd component at the head of the first c 1 c 1 c 2 Net Force: when more than one force acts! algebraic sum! head to tail method 1) draw vectors to scale 2) place the tail of the 2nd component at the head of the first 3) the resultant is from the tail of the first to the head of the 2nd c 2 c 1 c 2 c 1 R 11

12 Net Force: when more than one force acts! algebraic sum! head to tail method c 2 1) draw vectors to scale 2) place the tail of the 2nd component at the head of the first 3) the resultant is from the head of the first to the tail of the 2nd c

13 Vectors: size and direction 13

14 Net force: "sum of" the forces acting combination of all forces acting a b b a a b a b measured in Newtons (N) b b a a R R b a R b R a 14

15 2.5 The Equilibrium Rule the stretching force is called "tension" Note the mass is at rest!!!! tension weight the stretching force is called "tension"... Note the mass is at rest!!!! tension weight That's Newton's 1 st Law of Motion! ΣF = 0 Rest or v c means that ΣF = 0 15

16 .... T 2 T 2 F w1 F w F w2 ΣF = T 2 = 700 N T 2 = 600 N F w1 = 500 N Fw = 200 N F w2 = 600 N ΣF = 0 16

17 .... T 2 = 700 N T 2 = 600 N F w1 = 500 N Fw = 200 N F w2 = 600 N ΣF = Support Force weight: Force of gravity on an object F w = mg F N support: Force object (like the table) pushes back with (reactive) F w normal: The part of the support that is 90 0 from the surface 17

18 mattresstime.blogspot.com catalog.flatworldknowledge.com 2.6 Support Force What are all the forces? F N F s F ws F w 18

19 2.7 Equilibrium of Moving Things ΣF = 0 1 st Law...an object in motion will stay in motion in a straight line at a constant velocity UNLESS acted on by an outside force Equilibrium of Moving Things ΣF =

20 2.8 The Moving Earth Copernicus inertia not understood??? amount of force needed to keep it moving 30 km/s...107,000 Km/hr convertible vs sedan 20

21 slideplayer.com 21