Transcript Energy - Dr. Haleys Physics Class

Energy
 Energy
 Any
is the ability to do work.
object that has energy has the
ability to create force.
Energy

There are many different forms of energy:
Mechanical Energy
 Radiant Energy (Light)
 Nuclear Energy
 Electrical Energy
 Chemical Energy
 Thermal Energy (Heat)
 Pressure Energy
 Etc…

Energy
All forms of energy can be
classified into Potential or Kinetic.
Energy

Potential energy is the stored energy of
position possessed by an object.
Energy

Gravitational potential energy (GPE) is
the energy stored in an object as the result
of its vertical position or height.
Energy
These are both the same formula, but the top one is how it
looks on your formula chart. Make note of units.
Energy
What has more GPE, a rock at the top of a
a 50 m ramp or a rock on the top of a 55 m
ramp?
 If you double the height a stone that is
being held above the ground, what
happens to its GPE?
 If you half the height a stone that is being
held above the ground, what happens to
its GPE?

Energy

A 2 kg dog is at the top of a 3 m tall slide.
Calculate his GPE.
Energy

A 2 kg dog is at the top of a 3 m tall slide.
Calculate his GPE.
m= 2 kg
g= 9.8 m/s2
h= 3 m
GPE = mgh
GPE = (2)(9.8)(3)
GPE = 58.8 J
Energy

Elastic potential energy (PEe) is the
energy stored in elastic materials as the
result of their stretching or compressing.
 Elastic potential energy is
stored in the spring when
stretched (more
stretch=more energy)
 If
a spring is not stretched
or compressed no potential
energy is being stored; it is
in equilibrium
Energy

k = Spring constant (N/m)


The stiffer the spring, the larger the spring constant
x = Amount of compression relative to the
equilibrium position
Energy
A spring is stretched 0.2 m from
equilibrium. The force constant (k)
of the spring is 2500 N/m. What is
the potential energy of the spring?
Energy
A spring is stretched 0.2 m from equilibrium.
The force constant (k) of the spring is 2500
N/m. What is the potential energy of the
spring?
k= 2500 N/m
x= .2 m
PEe= ½(2500)(.2)2
PEe= 50 J
Energy

Kinetic energy (KE) is the energy of
motion.

The more an object moves, the more kinetic
energy it has.
Energy
Energy

Determine the kinetic energy of a 625-kg
roller coaster car that is moving with a
speed of 18.3 m/s.
Energy

Determine the kinetic energy of a 625 kg
roller coaster car that is moving with a
speed of 18.3 m/s.
m= 625 kg
v= 18.3 m/s
KE= ½ mv2
KE = ½ (625)(18.3)2
KE = 104,653.13 J
Energy

Mechanical energy is the energy that is
possessed by an object due to its motion or
due to its position. It can be kinetic or
potential.

Total Mechanical Energy (TME)= Potential
Energy+ Kinetic Energy
TME= (½ mv2)+(mgh)
Energy
TME= (½ mv2)+(mgh)
•
A golfer hits a 0.4kg golf ball with a speed
of 0.4m/s to a height of 30 m. What is the
golf ball's total mechanical energy?
TME= (½ mv2)+(mgh)
•
A golfer hits a 0.4kg golf ball with a speed
of 0.4m/s to a height of 30 m. What is the
golf ball's total mechanical energy?
m= .4 kg
v= .4 m/s
g= 9.8 m/s2
h= 30 m
TME= (½ mv2)+(mgh)
TME = (½*.4*.42)+(.4*9.8*30)
TME = 117.63 J
Conservation of Energy
 What
happens to the energy of
a ball when you throw it in the
air?
Think about Kinetic and
Potential Energy
Conservation of Energy

When you throw a ball in the air, the
energy transforms from kinetic to potential
and then back to kinetic.
What is happening to the
energy in this system?
Where is PE the greatest?
Where is KE the greatest?
Energy

The Law of Conservation of Energy:
 the total amount of energy in an isolated
system remains constant over time
 energy can neither be created nor
destroyed: it can only be transformed
from one state to another.
Remember the Lion King slide…
Energy Conservation
One of the most common conversions
is the changing of potential energy to
kinetic energy or the reverse.
•
How does friction play a role in
energy conservation?

Energy
KEi
PEi
KEf
PEf
((½ mv2)i+(mgh)i) = ((½ mv2)f+(mgh)f)
Energy

Julie has a mass of 49 kg. What is her potential
energy (PEi) when standing on the 6 meter
diving board? Julie jumps off the diving board,
what is her kinetic energy (KEf ) just before she
hits the water?

Julie has a mass of 49 kg. What is her potential
energy when standing on the 6 meter diving
board? (She is 6 meters above the water.)
m= 49 kg
h= 6 m
g= 9.8 m/s2

GPE =(49)(9.8)(6)
GPEi = 2,881.2 J
What is her KEi?
Julie jumps off the diving board. What is her
kinetic energy (KEf ) just before she hits the
water?
KEi PEi
PEf
m= 49 kg
0 + 2,881.2 = KEf + 0
h= 6 m
2,881.2 = KEf
g= 9.8 m/s2

GPEi= 2,881.2 J
KEi= 0 J
Energy


Work-Energy Principle - The change in
the kinetic energy of an object is equal to
the net work done on the object.
KEf
KEi
W = (½ mv2)f - (½ mv2)i
W = (½

2
mv )f
- (½
2
mv )i
A toy car with a mass of 2 kg starts at rest.
A spring performs 196 joules of work on
the car. What is the toy car’s final velocity?
W = (½ mv2)f - (½ mv2)i

A toy car with a mass of 2 kg starts at rest.
A spring performs 196 joules of work on
the car. What is the toy car’s final velocity?
m= 2
vi= 0
E=196
vf= ?
196 = (½ 2*vf2) - (½ 2*02)
196 = (1*vf2) – (0)
√196= √vf2
14=vf
Work The Following On A Sheet of Paper. You
must show all your work!! They are due before
you leave!!