Transcript Energy-Mechanical/Conservation

REVIEW
• To do the greatest amount
of work, you must apply
force (in the same
direction, at an angle) that
the object will move.
• If forces A, B, and C have
equal strengths, force (A,
B,C)will do the most work
because it is entirely in the
direction of the motion.
• In the same direction
• C
REVIEW- WORK
• A crane lifts a steel beam
with a mass of 1,500 kg.
• Calculate how much work
is done against gravity if
the beam is lifted 50
meters in the air.
• W= Fxd
=1500 kg(9.8m/s²)(50m)
=735 000 J
IT MAKES A DIFFERENCE HOW FAST
YOU DO WORK.
REVIEW
• A 70 kg person goes
up stairs 5 m high in
30 sec.
• a) How much power
does the person
need to use?
Power= work/time
=1143 W
• b) Compare the
power used with a
100-watt light bulb.
ENERGY EXISTS IN MANY FORMS AND
ALL ARE ABLE TO CONVERT TO ONE
ANOTHER
ENERGY- THE PROPERTY OF AN OBJECT
THAT ENABLES IT TO DO WORK
=
All forms of energy are
measured in Joules, a
unit of force that acts
over a distance
• Energy is measured in
the same units as
work because energy
is transferred during
the action of work.
DOING WORK ALWAYS MEANS
TRANSFERRING ENERGY
WHAT WOULD HAPPEN TO THE TEMP
OF THE SAND IF YOU SHOOK THE
CONTAINER?
PREDICT-WHAT WILL HAPPEN WHEN I
DROP THE TENNIS BALL AND BB
• 5 sentence persuasive essay
You need to persuade your partner to drop the bb
and tennis ball to demonstrate transfer of energy.
Tell them why it is soooo cool to do this.
Need 1) Topic sentence
2) 2 Facts
3) 1 opinion
4) Conclusion
AN EXAMPLE
• 1) The weather helps everything in some way,
shape or form.
• 2) The weather lets the plants grow when it rains.
• 3) It also provides us with drinkable water.
• 4) The weather is a very nice thing to have around.
• 5) In conclusion, the weather is very helpful and
useful to us all.
MECHANICAL ENERGY
(KINETIC AND POTENTIAL)
POTENTIAL ENERGY
IT HAS “THE POTENTIAL TO DO WORK”
POTENTIAL ENERGY
• An object may store energy b/c of its position or
shape
it is stored or held in readiness
GRAVITATIONAL POTENTIAL ENERGY
• Work is required to
elevate objects
against Earth’s
gravity
• The potential
energy due to
elevated positions is
called PEg
PEg =weight x height
mg
h
(GRAVITATIONAL) POTENTIAL ENERGY
• http://shelf3d.com/Jnj8mc04r9E#Potential Energy:
Wile E Coyote & Roadrunner
• PEg= mgh
=21 kg (
= 1 0290 J
)(50 m)
(GRAVITATIONAL) POTENTIAL ENERGY
• How much work is done by
the snowboarder (70 kg)at
the top of the mountain
when he has moved 10 m
horizontally?
• When he has moved down
the mountain 1000 m?
• PEg= mgh
=70 kg ( 9.8 m/s²)(1000 m)
•
= 686 000 Joules
KINETIC ENERGY
IT IS “CAPABLE OF DOING WORK”
KINETIC ENERGY
• The kinetic energy of a moving object
depends on two things: mass and speed.
KE= ½ mv²
KINETIC ENERGY
• Mathematically, kinetic energy increases as the
square of speed.
KE= ½ mv²
• If the speed of an object doubles, its kinetic energy
increases four times. (mass is constant)
KE= ½ MV²
• Note that the speed
is squared…
so if the speed is
double, the KE is
quadrupled
• 50 to 100 kph the
braking distance of
a car will increase
from 10 metres to 40
metres
WHEN THE BRAKES OF A MOTORCYCLE TRAVELING
AT 20 KM/H BECOME LOCKED, HOW MUCH
FARTHER WILL IT SKID IF IT TRAVELS AT 60 KM/H?
• KE= sliding distance
= 9x
AN ASSIGNMENT WITH YOUR PARTNER
• You have 15 minutes to find 4 situations using
potential and 4situations using kinetic energy
• You will work in groups of 2
• You will draw them and label them. What is
happening and where it occurred.
• Use level 1 voices.
SCAVENGER HUNT
EXAMPLES OF KINETIC ENERGY
1) Door closing
2)
Room 123, English hall
EXAMPLES OF POTENTIAL ENERGY
LAW OF CONSERVATION OF MATTER
• As energy takes different forms and changes things
by doing work, nature keeps perfect track of the
total.
• No new energy is created and no existing energy is
destroyed.
LAW OF CONSERVATION OF ENERGY
• A wind turbine is turned
with a constant force.
How much work is
done on the object?
• The work done on
the object is the
same amount that is
gained in kinetic
and heat energy by
the object
KE=PE
½ mv² = mgh
WORK-ENERGY THEOREM
What does this picture tell us?
http://www.pixton.com/comic/iq68urey
WORKΔENERGY THEOREM
• Whenever work is
done, energy
changes
• The amount of work
done on an object=
the amount of
energy gained by
the object
AN ASSIGNMENT WITH YOUR PARTNER
• Draw 6 situations
where there are
energy
transfers…you
cannot use any
examples from the
powerpoints