# Shared Flashcard Set

## Details

2-D Motion, Laws of Motion
Unit 2
35
Physics
10/13/2011

Term
 State, discuss, and give examples of Newton's first law of motion
Definition
 1st--law of inertia an object at rest and an object in motion at constant speed and sirection will remain so unless acted upon by a net external forcea=0inertia is a resistance to an object's change in velocityex: pulling a table cloth out from under dishes
Term
 State, discuss, and give examples of Newton's second law of motion
Definition
 2nd law--Fnet=ma, if there is a net force on a mass it must be acceleratingif Fnet=0, a=0if you keep mass constant, F proportional to aif you keep force constant, m proportional to 1/aforce is defined as the act necessary to make a mass accelerate lineralyex: pushing a block along a table
Term
 State, discuss, and give examples of Newton's third law of motion
Definition
 3rd--action-reaction, forces occur in equal and opposite pairs(on and by)ex: a--force BY earth ON moon r--force ON earth BY moonexternal force only concered with ON forces
Term
 Compare the velocity in the x- and y-direction for projectile motion
Definition
 inital velocity has both x- and y-componentsx-component of velocity stays constant, no a in the x-directionVx=VocosΘy-component at top Vy=0 then increase in the negative direction from that pointVy=VosinΘ-gt
Term
 using velocity vectors, describe the motion of a ball in projectile motion
Definition
 velocity has an x- and y-componentVo also has x- and y-partsx-component always stays constant, but y part increases, reaches 0 at the top, and increases again but in the negative direction
Term
 How long does it take a ball in two dimensions to reach the top of its path? One dimension? Why are they different?
Definition
 2D: ttop=VosinΘ/g1D: ttoop=Vo/gDifference: Because in 1D motion v=0 at the top..in 2D motion, Vy=0, but Vx=constant, so V does not =0 have to consider the angle Θ
Term
 what is a free body diagram?
Definition
 pictorial representation used to analyze the forces acting on a body of interest
Term
 Are mass and weight the same thing? how is weight calculated?
Definition
 No, mass is quantity of matter in an object or the measure of an objects inertionweight is the mass of an object times the gravitational pull of an objectW=mg
Term
 Define inertia
Definition
 a resistance to an object's change in velocity
Term
 define force
Definition
 the act necessary to make a mass accelerate lineraly
Term
 Define friction
Definition
 the force resisting the relative motion of surfaces sliding against each otherdependent on types of materials and normal forcef=µN
Term
 Define normal force
Definition
 force perpendicular to a surfaceforce BY resting surface ON object
Term
 Define coefficient of friction
Definition
 a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them togetherdepends on the materials used
Term
 Why does the equation for x not have g in the equation?
Definition
 Hooke's Law: F=kΔxbecause F proportional to x, constant is spring constant, k
Term
 Incline at angle Θ, what are components of weight parallel and perpendicular to the incline?
Definition
 parallel--mgsinΘperpendicular--mgcosΘ
Term
 If an object is at rest, what is known about that object?
Definition
 a=0Fnet=0N=mg
Term
 What are the forces acting on a kicked football at the top of its path?
Definition
 g is straight down towards earth, there is air drag (f)in the opposite direction of velocity
Term
 When Fnet is constant, how are m and a related?
Definition
 m α 1/a
Term
 When m is constant, how are Fnet and a related?
Definition
 F α a
Term
 compare static and kinetic friction
Definition
 fs is always larger than fk, it cannot be quantified except at fsmaxfk can be quantified, it stays constantwhen fs reaches its maximum point, it drops off to fk then becomes a constant fk
Term
 What makes a car go fast?
Definition
 acceleration is a vector, change in speed or change in directiongas pedal, steering wheel, etc
Term
 Can one pull themselves up by the boot straps?
Definition
 No, because in order to have acceleration there MUST be a net external force acting on the object(Force on you by you cannot happen)
Term
 Determine the action-reaction forces for Janet, Chair, and Keyboard
Definition
 A:Force BY janet ON chairR:Force ON janet BY chairA:Force BY janet ON keyboardR:Force ON janet BY keyboard
Term
 When is the normal force equal to the weight of the object? Not equal?
Definition
 On a flat surfaceOn an incline or when being pushed or pulled
Term
 Why is a box more difficult to push than pull?
Definition
 When pushing, normal force is weight plus force component, which makes N largerWhen pulling, N is mg minus force component, makes N smaller and therefore easier
Term
 Determine your mass in kg (1kg=2.2lb)
Definition
 117lb(1kg/2.2lb)=53.2kg
Term
 What keeps your book from falling through the table?
Definition
 Newton's law of motion explain it--no a, Fnet=0, because force up (N) is equal to force down (W)
Term
 What does Fnet mean?
Definition
 means if there is a net force acting on a mass that it must be accelerating
Term
 If an object has zero acceleration, are there no forces acting upon it?
Definition
 No, there may be forces acting on it that add to zero (N and mg=0)
Term
 If a brick is thrown through a window, describe the forces on the brick and the window.
Definition
 Action-Reaction forces, equal and opposite (NEVER cancel bc they act on different objects)A:Force BY brick ON windowR:Force ON brick BY window
Term
 Person jumps out of an airplane with a parachute. Describe the forces acting on the person, including friction
Definition
 mg down towards earth, friction up from the parachute and air drag
Term
 Why is it a good idea to wear seat belts in cars?
Definition
 If you slam on the breaks, F is throwing you forwards, friction from the seat belt will be a force acting opposite the force of your body forwards
Term
 Measure the coefficient of friction for a block of wood on a peice of wood
Definition
 Fnet=ma, at constant speed Fnet=0
Term
 Discuss Galileo's life
Definition
 1564-1642evidence of experimentally discovering laws of naturebook: "Dialogue of the Two Cheif World Systems"born in Italy, wrote in Italian and had his book mass produced, house arrest and blind for last several years of his life
Term
 Discuss Newton's life
Definition
 1642-1727discovered the laws of nature using mathematicswrote "Principa" elected a member of parliament, made warden of mint and introduced ridges on coins, remained active in mind and body until death but had emotional breakdowns
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