Transcript kinetic and potential energy

Energy and Work
Kinetic and Potential
Energy
Objectives
• You will be able to define and identify
Kinetic and Potential energy.
• You will be able to give examples of the
two forms of energy.
• You will be able to explain how one can
transfer to the other.
Definition of Energy…
The ability or capacity to do work.
Measured by the capability of doing work:
potential energy
or
the conversion of this capability to motion:
kinetic energy.
Units of Energy
• You use energy, its units are joules
• You do work, its units are also joules
– Work = force times a distance
W
F
D
Power
• Units are watts
• Power = work(or energy) / time
W
P
T
Potential Energy…
• Energy due to position or stored
energy.
Measure by:
PE= (weight) (gravity) (Height)
Potential energy is calculated by:
The object’s weight, multiplied by the earth’s gravitational pull (9.8 m/sec
sq), multiplied by the distance the object can fall.
Examples of Potential Energy:
Stretching a rubber band..
-Stores energy
Water at the top of a waterfall..
-Stores energy
Yo–Yo in held in your hand..
-Stores energy because of position
Drawing a Bow…
-Stores energy because of position
• When the position of an object is
altered it, creates Potential Energy.
• A yo-yo on the table, doesn’t have energy,
but when picked up, it alters its position
and now it has the ability (or potential) to
do work.
• A bow doesn’t have the capacity to do
work, unless it’s held at an elevated
position.
Potential Energy Converted
to Kinetic Energy…
When stored energy begins to move,
the object now transfers from
potential energy into kinetic energy.
Standing still
Running
Definition of Kinetic Energy…
The energy of motion.
Measured by:
2
KE= ½ (Mass) (Velocity)
Kinetic energy is calculated by one half of the object’s mass,
multiplied by the object’s speed- squared.
Examples of Kinetic Energy…
• Shooting a rubber
band.
• Water falling over
the fall.
• A Yo-Yo in motion.
• Releasing the arrow
from the bow.
POTENTIAL ENERGY
Energy stored or held in readiness
Most potential
THE TRADE OFF Between Potential
& Kinetic Energy
Summary of What You’ve
Learned..
•
•
•
•
Example using a coin:
Holding a coin in you hand, alters the coins
original position.
The coin has potential energy, because it
has ability to do work.
Dropping the coin in the bank, changes the
stored energy into motion.
This transfers the coin’s energy from
potential to kinetic energy.
TYPES OF ENERGY
• MECHANICAL
– Car, plane, wagon
• THERMAL
– Heat from moving molecules
– Inside all matter; furnace
• ELECTROMAGNETIC
– Visible light, microwaves, radio
waves
• CHEMICAL
– Batteries, matches,
body cells
• ELECTRICAL
– Lightning, power lines
• NUCLEAR
– Nuclear power plants,
atomic bomb, sun &
stars
Law of conservation of energy
• Energy cannot be
destroyed or created,
it can only be
transferred
• Convection –
movement of gases
by heat
• Conduction – lost by
touching
• Radiation – lost by
light
• Most energy is lost to
heat such as friction