LEARNING OBJECTIVES:

1. I will be able to use Newton's 1st and 3rd Laws to provide qualitative interpretations of force/object ineractions after today's class.

2. I will be able to use Newton's 2nd Law (Be sure to use the SUM of the forces in each dimension and NOT just F=ma) and my knowledge of vectors to provide quantitative analysis of force/object interactions after today's class.

3. I will be able to add friction to each of our problem types during today's class.

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WORDS O' THE DAY:

1. Newtons ("a unit of force" with units of (kg)(m/sec²) (Newtons are vector quantities so the direction in which the force is exerted on an object is crucial)

2. Normal Force ("Perpindicular Force")

3. Weight ("mass multipled by gravity") weight is NOT equal to mass, this takes some getting used to.

4. Equilibrium ("Forces Balance!")

FORMULAE OBJECTUS:

• Newton's 2nd: ∑F_x = ma_x; ∑F_y = ma_y
• friction: f = μN (friction is FUN) = the coefficient of friction times the NORMAL force.

WORK O' THE DAY:

LAB Error Analysis - Mea Culpa (*sigh* quick note)

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Also -- In years past the AP has *recomended* that you save a "few" example lab reports to support a passing for credit (4 or 5) score IF you are asked to provide them to your college/university.... I'm checking on that.

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• Review force diagrams (often called "free body diagrams")
• Review friction:

Friction ALWAYS opposes forward motion. That is to say it is 100% directed against the motion of the object regardless of whether it is air molecules pressing against an object in flight or a falling object or atoms/molecules catching against each other when two objects roll or slide against each other.

Air friction can be a beast (we may take a swing at the differential equation needed to solve for that much later) so we'll constrain ourselves to working with:

static friction (f_s) -- which seems kind of odd. Static friction is the force required to overcome the the atomic/molecular grabbing/sticking that occurs WHENEVER two objects slide against each other.

It may interest you to know that friction is SO important to science and industry that there are massive tables of frictional coefficients published. Let's take a gander at the venerable old CRC Handbook... now in it's 99th edition!

kinetic friction (f_k) -- which is the frictional force that exists between two objects sliding against each other AFTER they have been set into motion.

We will almost always be working with f_s

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