Newton’s Laws & Forces Review

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1. Galileo wrote this: Objects naturally tend to go in straight lines at

constant speed.◦ He IMAGINED no friction/air resistance◦ He knew air resistance actually depended on speed.◦ Late 16th Century

Newton: Objects maintain constant velocity,

UNLESS http://www.scitechantiques.com/cycloidhtml / http://www.youtube.com/watch?v=5C5_dOEyAfk

Newton’s 1st Law of Motion

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Unless something makes them CHANGE.

SF = “Net Force” (N)M mass (kg)

=change in motion

(Newton Called it)acceleration!! a (m/s2)

Newton’s 2nd Law (The one that matters.)

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Causes of Change (Net Force) = a (Motion Change)

Resistance to Change (Inertia/mass)

SF α a Given constant mass, Acceleration is proportional to the Net Force

(1/m) α a Given a constant net force, the acceleration is inversely proportional to the mass.

Newton II Continued . . .

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S is the Greek letter “S”. It means “sum” or “add up”.

Force- A push or a pull. Touching is not required. (Like magnets.) VECTOR

So SF is a sum of all forces acting on an object.

So what types of pushes and pulls do we have?

Net Force (SF)

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Force of Gravity (near an object) (Fundamental Force=Gravity)

◦ Fg =mg◦ g= 9.8 m/s^2 on Earth, 1.6 on Moon, 25 on Jupiter◦ M= mass in kilograms 2.2lbs.=1kg.◦ Acts straight down toward object.

Normal Force (Latin for 90 degrees) (Fundamental Force=Electromagnetic)

◦ FN= That depends.◦ It’s from electrons repelling electrons◦ It’s a “contact” force.◦ 90 degrees to the surfaces◦ Always found via SF=ma.◦ When 0 Normal Force, things aren’t “in contact”.

Types of Forces

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Friction (Fundamental Force=Electromagnetic)

◦ F=mFN OR f=mN

◦ Acts to RETARD motion (opposite your direction of motion)◦ Parallel to a Surface◦ Think of it as a translation from Normal Force to Sideways Force◦ Two types Static- An object is not moving, yet forces act. Kinetic- once the object is “slipping”, “skidding”, “sliding”. Static is usually greater than kinetic.

“Mu” is the coefficient of friction.

◦ms

◦mk

◦Depends on BOTH surfaces touching.

Types of Forces

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F.O.R.F.B.D.Force Table (x and y)F=ma (x and y)Finish the Formula

5 F’s of SF=ma

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b

Forces come in pairs. Forces are fundamentally an interaction

between 2 objects!

Fa,b=-Fb,a

Newton’s 3rd Law

a

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http://www.youtube.com/watch?v=UJiC7U3J3Jk

Something is conserved What could that be?

http://www.physicsclassroom.com/class/momentum/u4l2b.cfm

Newton’s Cradle