Download Energy - MADD Physical Science

WORK AND
ENERGY
WHAT IS ENERGY?
ENERGY AND WORK
Energy – ability to do work
When work is done, energy is
transferred
• You can only observed Energy
when it is being transferred
Joule is the unit for energy and
work
Remember – work is done only
when an object moves. W=Fd
But - energy can be present in an
object or a system when nothing is
happening.
However – it can only be observed
when it is transferred from one
object or system to another.
POTENTIAL ENERGY
AKA – Energy of Position
Potential Energy – Store energy.
Aka: energy of position
TYPES OF POTENTIAL ENERGY
Gravitational Potential Energy –
Energy stored due to position
(objects that are above Earth’s
surface).
Chemical Potential Energy – Energy
stored in chemical bonds such as
food or fuel.
Elastic Potential Energy – energy
stored by something that can stretch
or compress such as a rubber band or
spring.
GRAVITATIONAL
POTENTIAL ENERGY
AKA - GPE
Depends on mass and height.
GPE = m * g * h
Or
GPE = mass x free-fall acceleration x height
**note (mg = weight in Newtons)
)
GPE PRACTICE PROBLEM
A 65 kg rock climber ascends a cliff.
What is the climber’s gravitational
potential energy at a point 35 m above
the base of the cliff?
GPE = mgh
65kg = m
35 m = h
GPE = 65 x 9.8 x 35
2
9.8m/s = g
? = GPE
GPE = 22,295 J
GPE PRACTICE
1. A car with a mass of 1200 kg
top of a 42 m hill
at the
2. 2. A 65 kg climber on top of Mount
Everest (8800 m high)
3. 3. A 0.52 kg bird flying at an altitude of
550 m
KINETIC ENERGY
Kinetic Energy (KE) – energy of a moving
object due to its motion
KE = ½ x mass x velocity squared
KE = ½ mv2
Unit: Joule
Depends more on speed
than mass
KE PRACTICE
PROBLEM
What is the kinetic energy of a 44kg cheetah
running at 31 m/s?
44 kg = m
31 m/s = v
? = KE
2
KE = ½ m v 2
2
KE = ½ (44) x (31)
KE = 22 x 961
KE = 21142 J
KE PRACTICE
1. Calculate KE of a 1500 kg car
moving at 29 m/s; 18 m/s
2. If you use the sun as your frame
of reference, you always have
kinetic energy. Why?
FORMS OF ENERGY
All energy can be considered to be:
• Kinetic
• Potential
• Energy in fields (such as electromagnetic)
Major forms of energy are: mechanical,
thermal, chemical, electrical,
electromagnetic, and nuclear.
Each of these forms of energy can be
converted into other forms of energy
MECHANICAL ENERGY
 This energy is
associated with the
motion or position of
an object.
 The sum of potential
and kinetic energy in
a system
 (Usually involves
movement of an
object)
HEAT ENERGY (THERMAL)
 Energy of internal motion of atoms
 The faster the particles move, the more
heat energy is produced
 Usually results from friction
 Can cause changes in state of matter
CHEMICAL ENERGY
Energy stored in the chemical bonds .
When bonds are broken (reactions), this
energy is released
 Digestion(food), fuel(gas), battery
 Living things get energy from the Sun
 Plants use photosynthesis to turn energy
from sunlight into chemical energy
 When your body needs energy, organic
molecules are broken down by
respiration
ELECTROMAGNETIC
ENERGY
 Energy that travels through space in the
form of waves.
 Made up of moving electric charges;
moving electrons create magnetic fields
 Electricity, light, X rays, radio waves
 Light energy travels from Sun to Earth in
the form of electromagnetic waves
ELECTRICAL ENERGY:
 results from the flow of charged
particles or electrons.
 Electric charges can exert
forces that do work
NUCLEAR ENERGY
 energy stored in atomic nuclei –
 nuclear fission releases energy by
splitting nuclei apart,
 nuclear fusion releases energy by
combining 2 nuclei into a larger nuclei.
 Released in nuclear fusion (Sun)
WORK AND
ENERGY
9.4 CONSERVATION OF ENERGY
ENERGY CONVERSIONS
(TRANSFORMATIONS)
The process of changing energy
from one form to another.
Potential can become kinetic and
vice versa
EXAMPLES: ENERGY
TRANSFORMATIONS
Roller coaster: maximum potential at top
of hill, changes to kinetic as goes down,
maximum kinetic at bottom of hill
EXAMPLES OF
ENERGY TRANSFER
1. Driving a car- Gas (chemical energy) in a car
is used to produce heat (thermal energy) on
the motor and motion (mechanical energy) on
the car.
2. Running- transfers energy from food
(Chemical energy) to running motion
(mechanical energy)
3. Nuclear Power plants- atoms fuse together in
a nuclear reaction (nuclear energy) releasing
heat (thermal energy) which is used to create
electricity (electrical energy).
ENERGY
TRANSFORMATIONS
ENERGY
TRANSFORMATIONS
Flight of a ball: maximum
potential at top of the path,
maximum kinetic at bottom
•KE at bottom of the path equals
PE at top of the path
ENERGY
TRANSFORMATIONS
Bouncing ball: when it hits the ground,
kinetic is suddenly transferred to elastic
potential energy which then changes
back to kinetic as it bounces up
ENERGY
TRANSFORMATIONS
Mechanical Energy can change to
other forms
•When a ball bounces, not all of KE
changes to elastic PE (some is
transferred as sound and heat);
therefore with each bounce, it loses
some mechanical energy and doesn’t
bounce as high
LAW OF CONSERVATION OF
ENERGY
Law of conservation of energy – energy
cannot be created or destroyed; it only
changes form
Energy can be transferred to another
object/system or to another form
(potential to Kinetic)
ENERGY CONVERSION OF A
PENDULUM
1. How does potential energy
differ from kinetic energy?
2. How is the law of conservation
of energy demonstrated by the
movement of the pendulum?
3. Describe the relationship
between the kinetic energy and
the potential energy of a
swinging pendulum at their
highest and lowest points.
4. At what point in the pendulum's
swing is its gravitational
potential energy highest?
CONVERSIONS REVIEW
1.
Describe conversions between
potential and kinetic as a tennis ball
drops, hits the ground, and bounces
back up.
2. What energy conservations take place
in a pendulum? Why does it eventually
stop?
3. Describe the energy conversions that
take place when a flashlight is turned on.
4. Identify the conversions: An object is
raised and then allowed to fall. As it hits
the ground it stops, produces a sound,
and becomes warmer.