Transcript energy of

Force
• What is force?
– Push or Pull
• It’s what causes “things” to accelerate
1000 kg
Balanced v. Unbalanced
Forces
• If all forces are balanced there is no
acceleration in any direction.
– (Either Zero Motion or Constant Velocity)
• If one force is greater than the opposing
force we get acceleration in a direction.
Balanced Forces
(Balanced Forces = No Acceleration)
5N
Object
Notice that all the forces are equally pointed in
the opposite direction. Hence they balance
each other – or cancel each other.
5N
Equal Pushing
Forces may cancel each other and
produce No Acceleration!
Balanced Forces
(Balanced Forces = No Acceleration)
Ground pushes up
Gravity pulls down
Gravity pulls down on you…
The ground pushes back up…
THIS KEEPS YOU WHERE YOU ARE!
If these football players push
on each other equally as hard,
will either one move?
Balanced Forces
(Balanced Forces = No Acceleration)
5N
5N
Equal Pushing
Equal Pulling
5N
5N
Forces may cancel each other and
produce No Acceleration!
Unbalanced Forces
Causes Acceleration
Adding Forces
Subtracting Forces
Adding Forces
5N
5 N = 10 N
• Two forces can add together to produce a
larger net force than either original force.
– Positive Acceleration occurs (Speed up)
Unbalanced Forces
Causes Acceleration
Adding Forces
5N
Object
5N
Notice that all the forces are pointed in the
same direction. Hence they add together.
Subtracting Forces
10 N
=5N 5N
• Two forces can subtract to produce a net
force in the direction of the larger force.
– Negative Acceleration occurs (Slow Down)
Unbalanced Forces
Causes Acceleration
Subtracting Forces
5N
Object
5N
Notice that all the forces are unequal and
pointed in the opposite direction. Hence they
are unbalanced and in opposition to each
other – or one partially cancels the other.
5N
Balanced Forces
10N
10N
10N
Balanced
Push
i.e. Pushing a
Car
No Acceleration
10N
Balanced
Pull
i.e. Tug-o-war
No Acceleration
Un-Balanced Forces
Additive
10N
10N
Un-Balanced
Same
Direction
Faster
Acceleration
Un-Balanced
Opposite
Direction
Slower
Acceleration
Subtractive
10N
10N
10N
Balance between
Gravity and Friction
Q: If the friction of the air and the pull of
gravity were in perfect balance, what
would the skydiver be doing?
A: The skydiver would be going a constant
velocity (moving with no acceleration) down
towards the ground until it hit the ground.
The skydiver is colliding with the
molecules of gas in the air!
Which slows down the fall of the skydiver!
Accelerating
Constant
Velocity
Accelerating
Air
Resistance
30 m/s
28
25
m/s
20
10
0 m/s
Speed:
Constant Velocity
0 m/s
How it works
Notice that as the skydiver
leaves the plane, the force of
gravity accelerates him faster
towards the earth; however,
the moment he jumps out of
the plane, another force
begins to oppose gravity –
Air Resistance, (Friction).
This friction with the air
begins to slow down his rate
of acceleration. Meaning,
he’s still speeding up, just not
as fast.
Gravity
Once the force of air friction
equals the force of gravity,
the skydiver steadily
descends towards earth at a
constant velocity.
Balanced Forces
(Balanced
= No
Acceleration
)
Wait aForces
minute. This
object
was moving.
That’s Right. As you may have noticed, although I may have balanced forces, I might
still be moving.
Notice that when the forces are balanced, the object might still be moving, but the
objects are not accelerating, instead they have a constant velocity. Hence, once in
motion – it’s always in motion unless acted upon by what? Another Force.
5N
Notice that all the forces are equally pointed in
the opposite direction. Hence they balance
each other – or cancel each other.
Object
Equal Pushing
Equal Pulling
Forces may cancel each other and
produce No Acceleration!
0 1 2 3 4 56
Distance [m]
Constant Velocity
1
2
4
3
Time [Sec]
In other words, you still need to use the gas
peddle to balance out all the force of friction
to keep you going at a constant speed.
5N
5
Acceleration
1
2
To get an object to move faster, create an
unbalanced force!
5N
Force
• Speed = Distance divided by time
• S= D/T
• What is the speed of a rocket traveling at
4,000 miles in 1.5 hours?
2,667 miles/hr
The Law of Conservation of
Energy
created or
• Energy cannot be __________
____________;
it may be transformed
destroyed
from one form into another, but the total
never
amount of energy _________
changes.
What is energy?
• “the ability to do work”
• The combination of energy and matter
make up the universe:
– Matter is substance, and energy is the
mover
____________
of substance.
Energy is
nature’s way of keeping score.
We sense energy only
when it changes,
either a transformation
from one form of
energy to another,
or a transfer of energy
from one point to
another.
How is all energy divided?
All Energy
Potential
Energy
Gravitation
Potential
Energy
Elastic
Potential
Energy
Kinetic
Energy
Chemical
Potential
Energy
Potential
position
• energy of _________
or energy in
storage
______________.
– Water behind a dam
– Hammer over head
– Food on the plate
Kinetic
motion
• energy of ________,
the form capable of
doing work
– Flowing water
– A falling hammer
– Food being converted
into usable energy in
the cell.
PE = mgh
m = mass (kg)
____
h = height (m)
____
g = accel due
____
to gravity
(9.8 m/s2)
What is Gravitational Potential
o Potential energy
Energy?
due to an object’s
position
Don’t look down,
Rover!
Good boy!
mass
o P.E. = ________x
height x
________
gravity
_____________
What is Potential Energy?
o Energy that is stored
and waiting to be
used later
What is Elastic Potential Energy?
o Potential energy due compression or
expansion of an elastic object.
Notice the ball compressing
and expanding
What is Chemical Potential Energy?
o Potential energy
stored within the
chemical bonds of
an object
What is Kinetic Energy?
o Energy an object has due
to its motion
o K.E. = .5(mass x speed2)
KE = 1/2 m v2
•
•
•
•
4 kg bowling ball
at 10 m/s
= .5 (4kg) (10m/s)2
= 200 J
•
•
•
•
.25 kg baseball
at 50 m/s
= .5 (.25kg) (50 m/s)2
= 312 J
Courtesy Jerry Ohlinger’s Movie Material Store
Work is done when a force is
exerted over a distance.
Work
• is equal to the force that is exerted
multiplied by the distance over which it is
exerted.
Fxd
• W = _______
• The unit of work combines the unit of
force (N) with the unit of distance (m)
Joule
• Newton-meter (N-m) aka ________.
You carry a 20 kg suitcase upstairs, a
distance of 4m. How much work did you
do?
• W=Fxd
• F = ma
• = (20 kg) (10m/s2) = 200 N
• W=Fxd
• = (200 N) (4m)
• = 800 J
6 fundamental forms of energy
1.
2.
3.
4.
5.
6.
mechanical energy
Thermal (heat) energy
electromagnetic energy
electrical energy
nuclear energy
chemical energy
What is the source of our
energy?
• The source of
practically all
our energy is
the _______
SUN .
What is Mechanical Energy?
o Energy due to a
motion
object’s _________
position
(kinetic) or __________
(potential).
The bowling ball has
mechanical energy.
When the ball strikes
the pins, mechanical
energy is transferred
to the pins!
Examples of Mechanical Energy
What is Electromagnetic
Energy?
Light energy
o _________________
o Includes energy from
gamma rays, xrays,
ultraviolet rays,
visible light, infrared
rays, microwave and
radio bands
What is Electrical Energy?
o Energy caused by
the movement of
electrons
_____________
o Easily transported
through power lines
and converted into
other forms of
energy
What is Chemical Energy?
o Energy that is
available for release
from
_____________________.
Chemical reactions
The chemical bonds in
a matchstick store
energy that is
transformed into
thermal energy when
the match is struck.
Examples of Chemical Energy
What is Thermal Energy?
o
Heat energy
o The heat energy of an
object determines how
active its atoms are.
A hot object is one whose atoms
and molecules are excited
and show rapid movement.
A cooler object's molecules and
atoms will show less
movement.
QUIZ TIME!
What type of energy
cooks food in a
microwave oven?
ELECTROMAGNETIC
ENERGY
What type of energy is
the spinning plate
inside of a microwave
oven?
MECHANICAL ENERGY
QUIZ TIME!
Electrical energy is
transported to your house
through power lines.
When you plug an electric fan
to a power outlet, electrical
energy is transform into
what type of energy?
MECHANICAL ENERGY
QUIZ TIME!
What energy transformation
occurs when an electric lamp
is turned on?
ELECTRICAL ENERGY

ELECTROMAGNETIC ENERGY
What types of energy are shown below?
Mechanical and Thermal Energy
(Don’t forget friction)
What type of energy is shown below?
Chemical Energy
What types of energy are shown below?
Electrical, Mechanical and
Electromagnetic Energy
What type of energy is shown below?
Chemical Energy (yummy)
What type of energy is shown below?
Thermal Energy
What types of energy are shown below?
Mechanical, Electromagnetic,
Electrical, Chemical and Thermal
Energy
The Law of Conservation of
Energy
• Energy cannot be created or destroyed; it
may be transformed from one form into
another, but the total amount of energy
never changes.