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forces Flashcards

1
Q

when is work done

A

Work is donewhen an objectis movedover a distanceby a forceappliedin thedirectionof
its displacement

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2
Q

work done equation

A

work done (joules) = force (Newtons) * distance (m)

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3
Q

1 J = ?

A

1 Joule = 1 Newton metre

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4
Q

force and direction

A

Ifa forceacts in thedirection that an objectis moving,then theobjectwillgain energy

Iftheforceacts in theoppositedirection tothemovementthen theobjectwill loseenergy

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5
Q

how is nrg transferred to gpe nrg store of obj

A

mechancially

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6
Q

when friction is present wat happens

A

When friction is present, energy is transferredby heating
This raises thetemperature(energy is transferredtothethermal store) oftheobject
andits surroundings
Theworkdoneagainstthefrictionalforces causes this risein thetemperature

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7
Q

how does friction occur

A

Imperfections attheinterfacebetween theobject andthesurfacebumpintoandrubup
againsteach other
Notonlydoes this slow theobjectdown but alsocauses a transferofenergy tothe
thermal storeoftheobject andthesurroundings

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8
Q

air resisitance - what happens

A

Particles bumpintotheobject as itmoves through theair
As a result, energy is transferredby heatingduetotheworkdoneagainstthefrictional
forces

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9
Q

stationary objects - how many forces must be applied to change their shape?

A

For stationaryobjects, morethan oneforcehas tobeappliedtochangetheir shape

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10
Q

how can shape of obj change by

A

Their shapecan changeby:
Stretching(forces in oppositedirections away from theobject)
Bending(forces thatdistorttheobject)
Compressing(forces in oppositedirections towards theobject)

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11
Q

compression

A

An exampleofcompression is placinga mass on topofa springplacedon a flat surface

Thetwoforces are:
Theweightofthemass
Thereaction forcefrom thesurfacetothespring

the 2 forces are towards each other

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12
Q

stretching

A

An exampleof stretchingis placinga mass on thebottom ofa vertically hangingspring
Thetwoforces are:
Theweightofthemass
Thetension in thespring

forces are away from each othr

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13
Q

bending

A

An exampleofbendingis a divingboardbendingwhen a swimmer stands atthefarend
Thetwoforces are:
Theweightoftheswimmer
Thereaction forcefrom theblock tothedividingboard

forces act towards each other, but at different points on obj.

bending can alos be cuased by two forces at angle to each other

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14
Q

changes of shape

A

Achangeof shapeis calleda deformation andcan eitherbe:
Elastic
Inelastic

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15
Q

elastic deformaton

A

Whenobjects return totheiroriginal shapewhen thestretchingforceis removed
Examples ofmaterials that undergoelasticdeformation are:
Rubberbands
Fabrics
Steel springs

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16
Q

inelastic deformation

A

Whenobjects remain stretched and donot return completely totheiroriginal shape
even when thestretchingforceis removed

Examples ofmaterials that undergoinelasticdeformation are:
Plastic
Clay
Glass

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17
Q

hookes law

A

Therelationshipbetween theextension ofan elasticobject andtheappliedforceis defined
by Hooke’s Law

Hooke’s Law states that:
Theextensionof an elasticobject is directlyproportional totheforceapplied, up
tothelimit of proportionality

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18
Q

limit of proportionality

A

Thelimit of proportionality is whereifmoreforceis added,theobjectmay extendbutwill
not return toits original shapewhen theforceis removed(itwillbeinelasticallydeformed)
This varies accordingtothematerial

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19
Q

hookes lae eqaution

A

f = k * e

Where:
F =forcein newtons (N)
k=springconstantin newtons permetres (N/m)
e =extension in metres (m)

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20
Q

spring constant

A

how stif a spring is

higher the spring const, higher the stiffness

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21
Q

hookes law on graph

A

Hooke’s law is thelinearrelationshipbetween forceandextension
This is representedby a straight lineon a force-extension graph

materials not obeying this have non inear relationship - represenyed by curve on graph

Any materialbeyondits limitofproportionality will havea non-linearrelationshipbetween
forceandextension

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22
Q

spring constant from a graph

A

Iftheforceis on they axis andtheextension on thex axis,thespringconstantis the
gradient ofthestraight line(Hooke’s law) region ofthegraph

Iftheforceis on thex axis andtheextension on they axis,thespringconstantis 1 ÷gradient
ofthestraight line(Hooke’s law) region ofthegraph

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23
Q

elastic pot nrg

A

Theenergy stored in an elasticobject when work is doneon theobject

Providedthespringis notinelasticallydeformed(i.ehas notexceededits limitof
proportionality),theworkdoneon thespringandits elasticpotentialenergy storedare
equal

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24
Q

equation elsastic pot nrg

A

1/2 k e^2

Where:
E =elasticpotentialenergy in joules (J)
k=springconstantin newtons permetre(N/m)
e =extension in metres (m)

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25
Q

what is elastic pot nrg eq for

A

This equation is only for springs that havenotbeen stretchedbeyondtheirlimit of
proportionality

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26
Q

displacement

A

Displacement is a measureofhow far somethingis from its startingposition, alongwith its
direction

it is a vector

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27
Q

speed

A

scalar quantity

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28
Q

factors affecting speed

A

Age
Terrain
Fitness
Distance

for vehicles:
Shape
Design
Cost
Purpose

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29
Q

speed of sound

A

330 m/s

1500m/s in seawater

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30
Q

velocity

A

vector force

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31
Q

vlecoity- circular motion

A

when obj travels along circular path, velocity always changing

speed may be constant
direction always changing

32
Q

distance time graph

A

straight line - constant speed
slope of straight line - magnitude of peed (steeper the line, faster the speed)
horizonalline - obj is stationary

curve - speed is changing

gradient of the line is the speed of the obj

33
Q

instantaneous pseed

A

to calcualte speed at point in time use tangent

34
Q

acceleration

A

rate of change of velocity

acc = delta velocity/time

acc = m/s^2
delta v = m/s
spd = s

35
Q

acceleration - up and down

A

speed up - positive acc
speed don - neg acc

36
Q

Veolcity time graph

A

straight line - const acc
slope - magnitude of acc
(steeper the slope, higher the acc)
flat line - const velocity

acc - gradient of the graph
area under velocity time graph - distance travelled

37
Q

uniform (constant) acc

A

v^2= u^2 + 2as

Where:
s =distancetravelledin metres (m)
u =initial speedin metres per second(m/s)
v =final speedin metres per second(m/s)
a =acceleration in metres per secondsquared(m/s )

used for when time is not knon

38
Q

freefall

A

In theabsenceofairresistance, allobjects fallwith thesameacceleration
This is calledtheaccelerationduetogravity:

acc due to graviy = 9.8m/s^2

39
Q

how to work out weight from freefall

A

acc due to gravity * mass = weight

40
Q

terminal velocity

A

When a skydiverjumps outofa plane, twoforces act:
Weight (duetogravity)
Airresistance(duetofriction)

as they fall, air resiistance increases
one air resistance = weight, no more resultant force.
now they fall at const speed which is their terminal velocity

therefore smaller the weight of obj, smaller th terminal velocity

41
Q

newton first law of motion

A

Newton’s first lawof motion states:
Objects willremain at rest, or movewith a constant velocity unless acted onby a
resultant force

This means iftheresultantforceactingon an objectis zero:
Theobjectwillremain stationary ifitwas stationarybefore
Theobjectwillcontinuetomoveatthesamevelocity ifitwas moving

42
Q

newton second law of motion

A

Newton’s second lawof motion states:
Theaccelerationof anobject is proportional totheresultant forceactingon it and
inverselyproportional totheobject’s mass

43
Q

what does netwtonn 2nd law of motion eplain

A

An objectwill accelerate(changeits velocity) in responsetoa resultant force
Thebiggerthis resultantforce,thelargertheacceleration
For a given force,thegreatertheobject’s mass,thesmallertheacceleration
experienced

44
Q

fore and acc

A

force = mass * acc

force = netwton
mass = kg
acc = m/s^2

45
Q

newton 3rd law of motion

A

Whenever twobodies interact, theforces they exert on eachother areequal and
opposite

46
Q

what does newton third law explain

A

Allforces arisein pairs - ifobjectAexerts a forceon objectB,then objectBexerts an
equal andoppositeforceon objectA
Forcepairs areofthesametype- forexample, ifobjectAexerts a gravitational force
on objectB,then objectBexerts an equal andoppositegravitational forceon object
A

47
Q

inertia def

A

Thetendency of anobject tocontinuein its stateof rest, orin uniformmotion
unless acted uponby an external force

48
Q

inertia in more detail - when at rest and when in motion

A

In otherwords, inertia is an object’s resistancetoa changein motion
Ifan objectis at rest, itwilltendtoremain at rest
Ifan objectis movingat a constant velocity (constant speedin a straightline), itwill
continuetodoso

49
Q

intertial mass

A

Inertial mass is thepropertyofan objectwhich describes how diffcult itis tochangeits velocity

is the ratio between force applied and acc it experiences

50
Q

inertial mass eq

A

inertial mass = force / acc

inertial mass - kg
force - Netwons
acc - m/s^2

51
Q

stopping distance def

A

Thetotal distancetravelled duringthetimeit takes for a car tostop in responseto
someemergency

52
Q

stop dist eq

A

think dist + brake dist

all measured in metres

53
Q

reaction time def

A

Ameasureof howmuch timepasses between seeingsomethingand reactingtoit

54
Q

think dist def

A

Thedistancetravelled by a car fromwhen a driverrealises they need tobraketo
when they apply thebrakes

55
Q

think dist eq

A

speed of car * driver reaction time

56
Q

factors affecting think dist

A

car speed
tiredness
distractions
intoxication

57
Q

factors affecting brake dist

A

car speed
vehicle condition - worn tires, poor brakes
road condition - wet/icy roads harder to decelerate
vehicle mass

58
Q

braking and friction

A

when driver apply brakes, friction occur between brakes and wheels
meaning kin nrg of car decrs, thermal nrg brakes incrs

this means car decelerate

59
Q

braking force and spd

A

greater spd of vehicle, greater braking foce needed to be applied
this means decelration will be large as well

due to newton 2nd law motion

60
Q

danger large decleration

A

brakes overheating
loss of control of vehicle

61
Q

estim decelrationg forces

A

brake force * brake distance = 1/2 * mass * velocity^2

62
Q

calculting momentum

A

p = mv

p = momentum (kg m/s)
m = mass (kg)
v = velocity (m/s)

63
Q

what does momentum do

A

keep an obj moving in same direction
makes it difficult to change direction of obj with large momentum

momentum dpend on direction of travel
therefore can be pos or neg

if obj travelling right has pos momentum, obj going left has neg momejtm

64
Q

hen does momentum of obj change

A

if object accelerate or decelerate
if obj change direction
if obj mass changes

65
Q

conservation of momentum

A

Theprincipleofconservation ofmomentum states that:

In a closed system, thetotal momentumbeforean event is equal tothetotal
momentumafter theevent

Thetotal momentumbeforea collision=Thetotal momentumafter a collision

66
Q

what is a system

A

certian number of objects under consideration

can be 1 obj or multiple

67
Q

is momentum scalar or vector

A

vector

68
Q

is momentum conserved over time

A

always conserved over time

69
Q

since momenum is vector, system of obj moving in opp directions have what

A

if objs moving in opp dir at same speed, have overall momentum of 0 as they cancel out

70
Q

elastic collision

A

obj collid and move in opp dir

71
Q

inelastic collision

A

obj collide and move in same dir

72
Q

when elastic collision happen, the objs have

A

different velocity depending on its mass and initial momentum of system

73
Q

when inealstic collision happen, objs have

A

combined mass and velocity

74
Q

is momentum convervsed in collsion

A

always conserved in collsion

75
Q

when analysing a collsion what do you do

A

consider motion before and after collsion and state the velcoity of each obj and direction each obj moves

state whether collision was elastic or inelastic and explain

describe any energy transfers if kin nrg not conserved

76
Q

perfect elastic collsions

A

kin energy conserved - always equal

77
Q

perfect inelastic collsion

A

two objs stick together after colliding

science organisation (9 decks)

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