Lecture 12 Newton’s Laws of Motion

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Amount the contractors have collected during that time: $50,000,000

QUIZ Find this vector’s magnitude and angle with respect to the positive x axis and draw it Find the x- and y-components of the vector

What Causes Motion? In the absence of any forces acting on it, an object will continue moving forever. Motion needs no “cause.” Slide 4-8

Slide 4-9 Seat Belts: An Application of Newton’s First Law

Catalogue of Forces

Spring Force F sp Slide 4-13 

Tension Force Slide 4-14

Normal Force Slide 4-15

Slide 4-16 Friction f k and 

Drag and Thrust Slide 4-17

Example A block is dragged uphill by a rope. Identify all forces acting on the block. Slide 4-19

Exercise A ball, hanging from the ceiling by a string, is pulled back and released. Identify the forces acting on it just after its release. Slide 4-21

Newton’s Second Law Physics added to motion:

Example An elevator, lifted by a cable, is going up at a steady speed. Identify the forces acting on the elevator. Is T greater than, equal to, or less than w? Or is there not enough information to tell? Slide 4-23

Free body diagrams Make diagram of object showing all forces acting on it (as vectors). For now object will be represented by a point. Decide on the x and y-axes Find x- and y-components of each force Find Show F NET on diagram

Problems due Today 3: 26, 28, 30, 33, 70, 72

Problems due Friday Reading: 4: 5-8 Problems: 4: CQ1, MC21, 4, 7, 8, 9, 10, 11