Transcript Kinetic Energy

Ch. 5
Energy
Ch. 5.1
Energy in
Mechanical and
Fluid Systems I
What is Energy?
A property of an object is a quality
or trait that belongs to it.
Examples include mass, volume,
weight, color and shape.
 Energy is also a property. Energy
is the property that enables an
object to do work.
 Types of energy that we will learn
about are kinetic, potential,
internal and total energy.
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Types of Energy
Kinetic energy is energy that a
moving object has because it is in
motion, so kinetic energy is energy
of motion.
 Potential energy is energy that an
object has because of its position
or condition. An object that is
stretched or an object held in place
above the ground have potential
energy.
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Types of Energy - 1
Internal energy is the sum of the
microscopic kinetic and potential
energies of all of the atoms and
molecules in a substance.
 The total energy in a substance or a
system is the sum of the kinetic,
potential and internal energies.
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Kinetic Energy
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Kinetic energy is energy in the form
of motion. The amount of kinetic
energy depends on the mass of the
object and its velocity.
Formula:
Kinetic Energy (KE) =
½ mass (½ m) x velocity2 (v2)
Units:
• Mass – kg
• Velocity – m/s
• Energy – Joule (J)
Kinetic Energy Calculations (Sample)
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Eric's bike has a mass of 12 kg and
he is riding at a velocity of 8 m/s.
What is the kinetic energy of the
bike?
KE = ?
m = 12 kg
V = 8 m/s
KE = ½m x v2
= ½(12 kg)(8 m/s)2
= 6 kg x 64 m/s
= 384 J
Ch. 5.2
Energy in
Mechanical and
Fluid Systems II
Potential Energy
Potential energy is energy stored in
a motionless object due to its
position or condition.
 Gravitational potential energy
(GPE) is energy stored in objects
that are in a position above the
ground and having stored energy
due to the force of gravity. An
example would be a ball held
suspended above ground.
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GPE Calculations
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The formula for gravitational
potential energy (GPE) is:
GPE = mass (m) x 9.8 m/s2 x height (h)
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Units:
Mass
– kilograms (kg)
Height – meters (m)
Acceleration of gravity – meters/second2 (m/s2)
Energy – Joules (J)
GPE Calculations (Sample)
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A beautiful glass vase sits on the mantle
of the fireplace at a height of 1.2 m
above the floor. If the mass of the vase
is 2.8 kg, what is its gravitational
potential energy?
GPE = m x 9.8 m/s2 x h
= 2.8 kg x 9.8 m/s2 x 1.2 m
GPE = ?
= 32.93 J
m = 2.8 kg
h = 1.2 m
Potential Energy - 1
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Elastic potential energy (EPE) is energy
due to the condition of being stretched
or compressed. Examples include a golf
ball being struck by a golf club and a
stretched bow string. The un-stretched
position is called the equilibrium
position.
The side of the ball compresses
when struck, then accelerates
off of the club as it returns to
normal shape.
The string stretches and causes
the arrow to accelerate as it
returns to its normal position.
Conservation of Energy

The law of conservation of energy
states that energy may change
from one form to another, but the
total amount of energy never
changes. An example would be a
swing or pendulum. As the swing
moves back and forth the energy is
continually converted from kinetic
to potential energy.
Bernoulli’s Principle
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Bernoulli’s principle states that as the
velocity of a fluid increases, the
pressure exerted by the fluid decreases.
In other words, the faster a fluid moves
the less pressure it exerts. Bernoulli’s
principle explains why planes can fly.
The shape of the wing
causes air to move faster
across the top, resulting
in higher pressure below
the wing. This is called lift.