# AQA Physics Unit 3

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• Created on: 21-04-11 16:43

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Unit 3 Physics
Turning Forces
Moment
s
The
turni
ng ef
fect
of
t
he f
orce
is
cal
led
the
mo ment
and
it
can
be
incr
eased
by
i
ncreasi
ng t
he si
ze of
t
he f
orce
or
the
perpendi
cul
ar
dis
tance.
Cent
re
of
mass
The
centr
e of
ma ss
of
an obj
ect
i
s where i
ts
mass
may t
hought
t
o be
concentrat
ed
and
w hen
a suspended
object
i
s i
n equi
li
bri
um
i
ts
cent
re
of
mass i
s di
rect
l
y
beneat
h i
ts
point
of
suspensi
on.
The
cent
re
of
mass
of
a s
y mmet
ri
cal
obj
ect
i
s al
ong
the
axi
s
of
symmet
ry.
Moment
s i
n bal
ance
The
pri
n c
ipl
e of
moment
s i
s t
hat
the
sum
of
the
anti
cl
ockwise
moment
any
poi
nt
is
the
sum of
t
he
cl
ockw i
se
mo ment
t
hat
poi
nt.
St
abi
li
ty
The
stabi
li
ty
of
an obj
ect
is
incr
eased by
ma ki
ng i
ts
base as
w i
de as
possi
ble
and
maki
ng
it
s cent
re
of
ma ss
as l
ow
as possi
ble.
An
object
wi
ll
t
end
to
toppl
e over
i
f
t
he l
i
n e
of
acti
on of
i
ts
w ei
ght
is
outs
ide i
ts
base.
Ci
rcul
ar
Mot
ion
For
an obj
ect
that
i
s movi
ng i
n a
cir
cle
at
a const
ant
speed i
n a
cir
cle,
t
he obj
ect
accel
erat
es const
antl
y t
owards
the
cen t
re
of
the
cir
cle
because i
t
is
const
antl
y
c
h angi
ng di
rect
ion
so t
he vel
oci
ty
is
constant
ly
changing.
A
centr
ipet
al
force
is
a c
e nt
reseeki
ng f
orc
e
and t
he cent
ri
pet
al
for
ce whi
ch i
s
needed
incr
eases as
the mass
or
the
speed
o f
t
he obj
ect
i
ncr
eases or
as
the
r
of
the
cir
cle
decreases.
Gravi
tat
ional
At
tr
act
ion
The
for
ce
of
gravi
ty
between 2
object
s i
s an
att
ract
ive
for
ce and t
he bi
gger
i
t
is
the
gr
eater
the
ma ss
of
each obj
ect
is
and t
he small
er
the di
stance
between
the
obj
ects.
The
gravi
tat
ional
f
iel
d st
rengt
h
on ear
th
is
10 New t
on's
per
kil
ogr
am and
on
the
mo on 1.
6N/kg.

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Pl
anet
ary
Orbi
ts
To
stay
in
orbi
t
at
a par
ti
cul
ar di
stance,
a
planet
must
mo ve
at
a par
ti
cular
speed
ar
ound t
h e
sun.
The
furt
her
a pl
anet
is
fr
om the s
u n,
t
he l
ess
it
s speed
is
as
it
moves ar
ound t

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An
e l
ect
ri
c motor
i
s desi
gned
to
use
the
mot
or
eff
ect
and
w e
can
cont
rol
t
he
s
p eed
of
an el
ectr
ic
mo t
or.
A
simple
mo tor
has
a r
ectangul
ar
co i
l
of
i
nsulat
ed wir
e and t
he coi
l
of
insul
ated
wi
re (
the
arma t
ure
coil
)
that
i
s f
orced
to
rotat

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The
li
fe
hist
ory
of
a st
ar
A
low mass
star
:
Prost
ar
Mai
n st
age
red
giant
whi
te
dwar
f
black
dwar
f
A
high
mass
star
:
Prost
ar
Mai
n st
age
red
giant
whi
te
dwar
f s
u per
nova
neut
ron
star
Wh en
a st
ar
is
born i
t
for
ms
out
of
clouds
o f
dust
and
g as
and t
hey gather
t
ogether
under
thei
r
ow n

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Li
ght
el
eme nt
s ar
e f
ormed
as a
resul
t
of
fusi
on
in
star
s and
heavy
element
s ar
e
f
ormed
w hen
a massi
ve
star
col
lapses
and
then
explodes
as a
super