Transcript Kinetic Energy

Energy
1. What is Energy?
• “Something” that enables an object to do
work.
• When you have “Energy” you can do work
• A. The amount of energy that an object has
is related to the amount of work the object
can do.
• The amount of energy can be precisely
measured
• B. SI unit is Joules (for energy
and work)
• Comes in various forms
2.
How do we get energy to do work??
• By eating
• A. When you are sick
and not feeling well, do
you have a lot of
energy to go shopping
or play basketball?
• No
• B. Why?
• Because we are not
eating.
3. What are the 2 main forces
of Energy?
• A. Potential
• 1.
• A.
Stored Energy
Has stored
ability to move
matter
• Kinetic
• 1.
Energy of
Motion
4. Types of Potential Energy
•
•
•
•
•
•
1.
2.
3.
4.
5.
6.
Gravitational
Elastic
Chemical
Nuclear
Magnetic
Electrostatic
5. What is Gravitational Potential Energy?
• Energy due to gravity
acting on an object
PE = mgh
m = mass in kg
g = acceleration due to
gravity (m/s2)
h = height in meters
Gravity = force of
attraction between
any 2 objects)
6. What is Elastic Potential Energy?
• Elasticity
• A. When stretching a rubber
band
• The potential energy is the
energy that powers the rapid
return to shorter original
length.
• B. Ball bouncing
• Round shape flattens as hits
ground – alters tension
• Then returns to round shape
and allows it to bounce
7. What is chemical potential energy?
• Energy stored within
the bonds of a
substance.
• Uses Conservation of
Mass – total amount of
matter does not
change
• Example:
• A. eat cheeseburger
• Gives energy to run
• B. gas in a car allows
it to move.
8. What is nuclear potential energy?
• Energy stored in the
bonds of subatomic
particles
• Either split (fission)or
fuse (fusion) of atoms
• Some mass is
transformed into
energy.
9. What is magnetic potential energy?
• Attraction or repulsion
from magnetic energy
stored in objects
• CME’s – coronal mass
emissions from sun’s
magnetic field
• Magnets – anything
with iron in it
10. What is electrostatic potential energy?
• Attraction or repulsion of
electrical charges
• Example: clean sock sticking
to clothes after it comes out
of a dryer
• Hair standing on
end
•
11. Types of Kinetic Energy
•
•
•
•
•
•
•
•
•
1. Mechanical
2. Thermal
3. Electrical
4. Nuclear
5. Sound
6. Electromagnetic
KE = 1/2mv2
M = mass in kilograms
V = velocity (m/s)
12. Mechanical Vs Non-Mechanical Energy
Mechanical Energy
• Non-Mechanical
• Energy that an object
has due to its motion
or position
• Mass is not displaced,
no movement or
velocity gained or lost
• Mass is, or will be,
displaced (moved)
• Examples
• Kinetic or Potential
• Heat energy (fire)
• Chemical Energy
• Gasoline
• Food
13. What is thermal energy?
• Total energy in a
substance measured in
units of heat or
temperature.
•
•
•
•
Examples:
A. Ice melting
B. Water boiling
C. Warm water in a
shower
• D. Frying an egg
14. What is electrical energy?
• Energy associated with
movement of charges
• Examples:
• A lit light bulb
• Ex. Lightning – electricity
• Positive and negative
charges collect in different
parts of clouds
• When there are a lot of
charges – get lightning
• Electricity travels between
areas of opposite charges
15. What is sound energy?
• Energy transmitted
through compression
of matter
• Examples:
• A. Hearing music
• B. Hearing thunder
16. What is electromagnetic energy?
• Energy that travels in
waves and can travel
in a vacuum
• A. Visible light
• B. Rainbow
• C. Radio waves
Sample Problem #1
6 kg
Gravitational Potential energy is
PE = (mass) x (Gravity) x ( Height )
= (6 kg)x (9.8 m/s2 ) x ( 20 m )
= 1176 Joules
What is potential energy at the bottom (zero
height)?
At a height of zero meters PE is zero Joules.
20 m
What is the potential energy of a 6kg bowling
ball at a height of 20 meters?
Kinetic Energy (KE)
• Energy associated
with an object due to
its motion.
• If something is in
motion it has the
ability to do work
• A stationary object
has zero kinetic
energy
2
KE = ½mv
KE= ½ x Mass x Speed2
Notice that speed is
squared, so a small
increase in speed will
result in a larger
increase in KE!
Sample Problem #2
6 kg
20 m
What is the kinetic energy of a 6kg
bowling ball, falling from a height of 20
meters just as it reaches the ground
with a speed of 19.8 m/s?
Kinetic energy is
(Kinetic Energy) = ½ ( Mass ) x ( Speed )2
= ½ x( 6 kg ) x ( 19.8 m/s )2
= 1176.1 Joules
20 m/s
17. Conservation of Energy
• Law of Conservation of Energy states that
energy can never be created or destroyed. It
can only be transformed from one form into
another.
• Example
• A book falls from a table
• A rubber band pulled back
• The total Mechanical Energy must always be
equal to the sum of Kinetic Energy and
Potential Energy
Etotal = KE + PE
Pendulum
“Like a child on a swing”
Energy exchange from PE to KE and back.
Maximum
Height
Check it out!
Can predict speed from height
since PE+KE constant
Maximum
Speed
Maximum
Height, again
More than Meets the Eye
Watch below as the KE and the
PE change as the car changes
height and speed. Notice that no
matter when you look at the two
bars, there is only the same
amount of energy that you
started with.
Watch This!
18. Check for Knowledge
• Suppose you have a 1 kg mass at a height of
1.25 m. How much potential energy does it
have?
• The mass is now let go. At the very bottom,
what is it’s kinetic energy?
• What is the speed of the mass just before it hits
the ground?