Law of Conservation of Energy Energy cannot be created or destroyed only changed from one form into another Imagine a ball being thrown up into the air As the ball travels upwards KE is converted into ID: 629763
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Slide1
T
h
e Law of Conservation Of EnergySlide2
Law of Conservation of Energy
:
Energy cannot be created or destroyed, only changed from one form into another.Slide3
Imagine a ball being thrown up into the air:
As the ball travels upwards
KE
is converted into
PE
As the ball falls downwards
PE
is converted into
KESlide4
This is similar to a pendulum:Slide5
On roller coasters the largest hill is always the first. Why is that?Slide6
When only conservative forces (like gravity) work on an object,
E
k
is converted into
E
p
and vice versa.
When external forces like friction are at work then energy is not conserved.
Friction converts some energy into heatSlide7
The Law of Conservation of Energy:
Since no energy is lost, the
total initial energy
must
equal
the
total final energy
:
ΔKE
= -
ΔPE
KE
i
+ PEi = KEf + PEf
½mv
i
2
+
mgh
i
= ½
mv
f
2
+
mgh
fSlide8
Ex:
While
jumping over The Great Wall of China an 82 kg
skateboarder
needs to leave the ramp traveling at 78 km/h.
a) How
much potential energy does he need to start with
?
b
) What minimum height of ramp should he use?Slide9
A trampoline dunk artist is
bounced
to
a maximum
vertical height of 4.8 m before launching himself towards the hoop. At the top of his arc he is 3.2 m above the ground.
How
fast is he traveling at this point?Slide10
A 65 kg snowboarder starts at rest, travels down a hill into a gulley and back up the other side as shown. Find his speed at the top of the 2
nd
hill.
45 m
25 m