Transcript KINETIC ENERGY

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POTENTIAL
ENERGY
Gravitational
Potential Energy
Depends
on height
Elastic Potential Energy
Associated
with objects
that can be
stretched or
compressed
CHEMICAL ENERGY
energy required to bond atoms together
NUCLEAR ENERGY
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released in
the form of
light and
heat
energy as
the nucleus
splits
Most concentrated form of energy
> 50,000 DEGREES CELSIUS
KINETIC ENERGY
MECHANICAL ENERGY
energy associated with motion
Movement of turbines
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Moving electric
charges
Internal
motion of
atoms
Heat energy causes changes in
the temperature and phase
(solid, liquid, gas) of any form
of matter
ENERGY
TRANSFORMATIONS
http://www.youtube.com/watch?v=RD_54Cq_UMM
Changes in Energy Video
http://172.25.31.139/index.asp?ResourceString=MSMC/Physics/
Media Server Online: Potential and Kinetic Energy
Energy cannot be created
nor destroyed. Energy is
converted from one form to
another.
CONSERVATION OF ENERGY
1-11 Lecture 11_ Work - Kinetic Ener.mp4
Law of CONSERVATION OF ENERGY
“Energy cannot be created
nor destroyed. Energy is
converted from one form to
another.”
PE =
max
max
KE
Videos on KE and Pe
• Kinetic & Potential Energy
What you know
•An object that has energy can do work.
•Work is done when energy is transferred
from one object to another or changed
from one form to another.
WORK
put in can
increase
P.E.
can do
K.E.
WORK AND ENERGY
1. max PE
= max KE
2. Work = Energy
3. Work = PE gained = KE
Work = KE
Units:
Energy and Work = joules (J) = Newton-meter (Nm)
Mass = kilograms (kg)
Weight = newtons (N)
Gravity constant = 9.8m/sec/sec ~ 10 m/sec/sec
Velocity = m/s
Height = meters (m)
1km = 1000m
1kg= 1000g
1hr= 3,600sec
Weight Vs. Mass
http://www.youtube.com/watch?v=grWG_U
4sgS8&feature=related
Weight and Mass
Weight is a measure of the
force of gravity on an object
Weight = Mass x acceleration
due to gravity
w= mg
POTENTIAL
ENERGY
ENERGY A BODY HAS
BECAUSE OF ITS POSITION
OR CONDITION
P.E.= Ep = mgh
G.P.E. = weight x height
KINETIC ENERGY
2
(E k) = ½ mv
2
mv
=
KE
2
Kinetic energy Ek or k.e. is the energy
that an object has because it is moving
Potential Energy:
PE or Ep or GPE = Weight x height (P.E. = w x h)
weight = m x g
or
= mass x gravity x height
(PE = m x g x h)
Kinetic Energy:
KE or Ek = ½ Mass x Velocity2 (K.E.= 1/2m x v2)
or
= m x v2
2
STEPS IN PROBLEM
SOLVING
 STEP 1. Write the formula
 STEP 2. Substitute given
numbers and units
 STEP 3. Solve for the
unknown.
EXAMPLE
What is the p.e. of a book of
mass 1200 g, resting on a shelf
2 m above the ground?
p.e. = mgh
p.e. = 1.2kg x 10m/s/s x 2m
p.e. = 12.0 N x 2 m
p.e. = 24 N-meter or Joules
SAMPLE PROBLEM:
A hiker weighing
680 N climbs 40 m
up a hill. Calculate
the gravitational
potential energy
gained at the top of
the climb.
Ep= wxh
Ep = 680 N x 40 m
= 27,200 N-m
or 27.2 KJ
Calculate the p.e. of a 40 kg iron
bar raised 1 m. (g = 10m/s/s)
identify the tricky part of this next Q:
2. Calculate the p.e. of a 65,000 g
boulder resting at 22 m above the
road.
Try this one:
3. How high is a .2 kg jar if it has 3J of
p.e.?
ANSWERS
1. Calculate the p.e. of a 40 kg iron
bar raised 1 m. 400 N-m or 400J
2. Calculate the p.e. of a 65,000 g
boulder resting at 22 m above
the road. 14,300 N-m or 14.3 KJ
3. How high is a .2 kg jar if it has 3J
of p.e.? 1.5 m
What is the Ek of an arrow
with a mass of 25 g
traveling at 25m/s?
What is the Ek of an arrow with a mass
of 25 gm traveling at 25m/s?
Answer:
k.e. = ½ mv2
= ½ x .025kg x (25m/s)2
= ½ x 0.025kg x 625m/s
= (0.5) 15.625
= 7.8125 Nm
but 1 Nm = 1J
= 7.8125 J
SUMMARY OF CONCEPTS: GPE = w x h or
GPE = mgh
•If h is doubled, the GPE is doubled.
If H is tripled, the GPE is also tripled.
•If speed (velocity) is doubled (2x), the Kinetic Energy
increases (4x or 22).
If speed (velocity) is tripled (3X), the KE increases 9x or 32.
• The GPE at the top changes to KE at the bottom.
KINETIC ENERGY
• The greater the speed the greater the
k.e. of the object
• The greater the mass of a moving
object, the greater the k.e. of the
object
POTENTIAL ENERGY
Ep or p.e. is the potential energy an
object has because of its height.
“The higher an object is lifted, the
greater its p.e.”
“The greater the mass of an object the
greater its p.e.”
the gain in p.e. = work done
Ep = W
Putting these formulae together:
Gain in Potential energy= work done lifting
Ep = W
= lifting force x distance lifted (height)
Ep = F x d (h)
= weight force x distance lifted
Ep = Fg x d (h)
(g = 10N/kg)
= mass of object x g x distance lifted
Ep = mgh
Video clip
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Conservation of Energy
AMUSEMENT
PARK PHYSICS
Applying potential and kinetic energy
Height
(h in
meters/m)
PE = m g h
E k = ½ m v2
ROLLER
COASTERS
http://www.funderstanding.com/K12/coaster/
http://dsc.discovery.com/convergence/c
oasters/interactive/interactive.html