ENERGY
-
Definition :
property that is transferred to an object when
work is done or heating up the
object
Energy is measured in Joules (J)
that can move/ in motion
HEAT
msi
mechanical
RCY TRANSFERS
radiation
↓ ↓
pushing, electrical electromagnetic
~
↓
pulling
waves
electricity, heating
electrons
↓
,
protons
not + cold
cold - not
Heating pathway
From the coffee
t
the
mug I
↓ surrounding
the hand
-RGY
CHANGE
teries (in a bulb circuit
chemical electrical
light thermala
,
- a -
energy energy
Driving a car
car battery) car is moving
Electrical ↓
energy
Kinetic thermal
+ y D
energy energy
chemical
energy
(petrol
Grinder
Electrical kinetic thermal
energy ·
-
energy energy
T ENERGY
* an object in motion has kinetic
energy
* Ex =
1 mv2
m = mass
(kg) EK = Kinetic (3)
energy
(m/s)
v =
velocity
Calculate the kinetic energy stored in a vehicle of mass 1200 kg moving
at a speed of 27 m/s.
Ex
!mrz
=
1200 22
-
=
x x
Ex =
430 I
CTATIONAL POTENTIAL
gravity => 9 .
8N/9 .
8 m/s2
*
object experience gravitational potential
energy when they are above ground/
earth's surface .
WORK
energy "Transferring from the
person to the object
H
result in a
change of only with
movement
MOTION x
(change the kinetic energy
V
When force is
applied to
more an object that WORK -
ENERGY
results in a change of DONE TRANSFER
MOTION .
W = Force x Distance (Nm/j)
W =
Fd
work
kinetic done
* same & gainenergy
J/NM
F =
Force Distance
movingIstarts
(F) -NX (d) -
m
* opp Close(Friction
#
energy wastage f o > gravitational
1)
-
(heat) energy potential energy
(less motion ) (high)
Kinetia
E
Force
3
:
weight work
done
distance =
height
Chigh)
Mitte
Light a
chemical -
> electrical - light
Bulb energy energy energy
↓
(wastage)
thermal
energy
chemical energy -
> electrical
energy -
thermal/ -
kinetic
C
mechanical
Heat
energy
energy energy
.
~
CONSERVING
ENERGY
The principle of conservation of energy states that:
Energy cannot be created or destroyed, it can only be
transferred from one store to another
Total
Energy transferred = total energy received
NO ENERGY IS LOST
↓
because energy is only transferred
BUT ,
energy can be
CATED
↓
waste energy/ spreading out
non-useful
to the surrounding
E
heat radiation
POWER
-
* Work done over time >
-
power is work done
unit time
per
* Power is work done over time .
7 Power of the
bulle
↓
the bulb is
energy
time .
using over
Power = Work done
Time
ofEnergy
Time
(3)(2/s)
(5)
(Watts)/W
WIE
(3)
=
P(w)
Y Tes
(d) (F)
Mike and Ian move 50 m on a snow lift which uses 750 N of force to move them in
75 seconds. Calculate the power of the lift.
(t)
E/WD
p :
Work done) =
Force x Distance
t
Energy
&
= 750NX 50m #
WD/E = 37500 NM/ P = 750x50
75
Wt
P = 37500(J)
>
P ow
75(5)
=
P = 500W
-
water
Tan is
heating by using a
500 heater for 10s . How much
energy is supplied to the .
water
work done
Energy = Power x Time
= 500W X I0S
E = 5000 J
-
-
CIENCY
converted into percentage
how much
energy/power converted usefully , compared hom much
wasted .
Efficiency = used energy
x 100% % of used
energy over
total total
output energy
energy
Total E Eused
A power drill uses 500J of electricity. Only 400J of kinetic energy was generated
by the drill. What is its efficiency?
4003
x
100 % = 20 % efficient for drilling
↓
5005
20% wasted energy
dissipated
E sound
·
heat
energy
·
Total E E used
A portable speaker coverts 150J of electrical energy into 30J of sound energy.
Calculate its efficiency.
38
X
100 % = 20% efficient for sound
150
80 % wasted
