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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
what is elastic pot nrg eq for
This equation is only for springs that havenotbeen stretchedbeyondtheirlimit of proportionality
26
displacement
Displacement is a measureofhow far somethingis from its startingposition, alongwith its direction it is a vector
27
speed
scalar quantity
28
factors affecting speed
Age Terrain Fitness Distance for vehicles: Shape Design Cost Purpose
29
speed of sound
330 m/s 1500m/s in seawater
30
velocity
vector force
31
vlecoity- circular motion
when obj travels along circular path, velocity always changing speed may be constant direction always changing
32
distance time graph
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
instantaneous pseed
to calcualte speed at point in time use tangent
34
acceleration
rate of change of velocity acc = delta velocity/time acc = m/s^2 delta v = m/s spd = s
35
acceleration - up and down
speed up - positive acc speed don - neg acc
36
Veolcity time graph
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
uniform (constant) acc
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
freefall
In theabsenceofairresistance, allobjects fallwith thesameacceleration This is calledtheaccelerationduetogravity: acc due to graviy = 9.8m/s^2
39
how to work out weight from freefall
acc due to gravity * mass = weight
40
terminal velocity
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
newton first law of motion
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
newton second law of motion
Newton's second lawof motion states: Theaccelerationof anobject is proportional totheresultant forceactingon it and inverselyproportional totheobject's mass
43
what does netwtonn 2nd law of motion eplain
An objectwill accelerate(changeits velocity) in responsetoa resultant force Thebiggerthis resultantforce,thelargertheacceleration For a given force,thegreatertheobject's mass,thesmallertheacceleration experienced
44
fore and acc
force = mass * acc force = netwton mass = kg acc = m/s^2
45
newton 3rd law of motion
Whenever twobodies interact, theforces they exert on eachother areequal and opposite
46
what does newton third law explain
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
inertia def
Thetendency of anobject tocontinuein its stateof rest, orin uniformmotion unless acted uponby an external force
48
inertia in more detail - when at rest and when in motion
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
intertial mass
Inertial mass is thepropertyofan objectwhich describes how diffcult itis tochangeits velocity is the ratio between force applied and acc it experiences
50
inertial mass eq
inertial mass = force / acc inertial mass - kg force - Netwons acc - m/s^2
51
stopping distance def
Thetotal distancetravelled duringthetimeit takes for a car tostop in responseto someemergency
52
stop dist eq
think dist + brake dist all measured in metres
53
reaction time def
Ameasureof howmuch timepasses between seeingsomethingand reactingtoit
54
think dist def
Thedistancetravelled by a car fromwhen a driverrealises they need tobraketo when they apply thebrakes
55
think dist eq
speed of car * driver reaction time
56
factors affecting think dist
car speed tiredness distractions intoxication
57
factors affecting brake dist
car speed vehicle condition - worn tires, poor brakes road condition - wet/icy roads harder to decelerate vehicle mass
58
braking and friction
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
braking force and spd
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
danger large decleration
brakes overheating loss of control of vehicle
61
estim decelrationg forces
brake force * brake distance = 1/2 * mass * velocity^2
62
calculting momentum
p = mv p = momentum (kg m/s) m = mass (kg) v = velocity (m/s)
63
what does momentum do
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
hen does momentum of obj change
if object accelerate or decelerate if obj change direction if obj mass changes
65
conservation of momentum
Theprincipleofconservation ofmomentum states that: In a closed system, thetotal momentumbeforean event is equal tothetotal momentumafter theevent Thetotal momentumbeforea collision=Thetotal momentumafter a collision
66
what is a system
certian number of objects under consideration can be 1 obj or multiple
67
is momentum scalar or vector
vector
68
is momentum conserved over time
always conserved over time
69
since momenum is vector, system of obj moving in opp directions have what
if objs moving in opp dir at same speed, have overall momentum of 0 as they cancel out
70
elastic collision
obj collid and move in opp dir
71
inelastic collision
obj collide and move in same dir
72
when elastic collision happen, the objs have
different velocity depending on its mass and initial momentum of system
73
when inealstic collision happen, objs have
combined mass and velocity
74
is momentum convervsed in collsion
always conserved in collsion
75
when analysing a collsion what do you do
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
perfect elastic collsions
kin energy conserved - always equal
77
perfect inelastic collsion
two objs stick together after colliding

science organisation (9 decks)

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