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All Energy
Potential
Energy
Gravitational
Potential
Energy
Elastic
Potential
Energy
Kinetic
Energy
Chemical
Potential
Energy
The basic motion of energy is stored work. A tankful of gas, a
heavy truck moving at speed, and a charged automobile
battery all possess energy.
  The energy associated with a mass in motion is called
kinetic energy
  The energy that is stored is called potential energy.
Potential Energy
Energy that is stored and waiting to be used later
Gravitational Potential Energy:
Potential energy due to an object’s position above the surface.
Formula
PE = m·g·h
m = mass
g = acceleration of gravity (9.81 m/s2 )
h = vertical component of displacement height
Units: Joules (J) or Ft-lbs
Example 1:
A crate of mass 5,000 kg is raised slowly to a height of 12 m
above its original position. What is the potential energy at
the height of 12m?
PE = m·g·h
PE = 5000 kg x 9.81 m/s2 x 12 m
PE = 588,600 J
Elastic Potential Energy
Potential energy due to compression or expansion of a
spring or an elastic object.
Bow and Arrow
Springs
Stretched Rubber band
Hooke's Law gives the
relationship between the
force applied to an
upstretched spring and the
amount the spring is
stretched.
•  Every spring has an elastic limit.
•  If the spring is stretched within its elastic limit, it
“springs” back to its “rest point”.
•  If a spring is stretched beyond its elastic limit, it becomes
deformed.
•  As illustrated below, the distance a spring is stretched is
called the “elongation”.
•  Robert Hooke was the first to discover that the spring
force is directly proportional to the elongation.
•  This relationship is known as Hooke’s Law.
Hooke’s Law formula:
F = k·x
F = the spring force (N)
k = the force constant (N / m)
x = the élongation of the spring from the resting point (m)
•  The force constant is the force required to stretch or
compress a given object.
•  The force constant is different for different springs and
depends upon the type of material the spring is made of as
well as the thickness of the spring coil.
•  The greater the value of the force constant, the “stiffer” the
spring.
•  Example
Elastic PE Formula:
PE = ½ k (Δx)2
k = Force constant (N/m)
Δx = distance the object has stretched or compressed (m)
Units: Joules (J) or Ft-lbs
Example #2
A coiled spring is stretched 0.05 m by a weight of 0.50 N hung
from one end.
1.  How far will the spring stretch if a 1.0 N weight replaces the
0.50 N weight?
2.  What weight will stretch the spring a distance of 0.03 m?
1.  0.1 m
2.  0.3 N
Example #3
Jan's mountain bike has a spring with a constant of 64 N/m in the
front-wheel suspension, and it compressed 0.17 m when she hit
a bump. How much energy does the front spring now store?
PE = ½ k (∆x)2
PE = ½ (64 N/m)(0.17 m)2
PE = 0.925 J
Example #4
A spring has 1.1 J of potential energy and was compressed 0.2
m. What is its spring constant?
PE = ½ k (∆x)2
1.1 J = ½ k (0.2 m)2
k = 55 N/m
Chemical Potential Energy
Potential energy stored within the chemical
bonds of an object
Energy an object due to its motion
Kinetic energy exists whenever an object which has mass is
in motion with some velocity.
The greater the mass or velocity of a moving object, the
more kinetic energy it has. Kinetic Energy Formula:
KE = ½ mv2
m = mass (kg)
V = Velocity (m/s)
Units: Joules (J) or Ft-lbs
Example #5:
What is the Kinetic Energy of a 1,000 kg car moving at 30 m/s?
KE = 450,000 J
Example #6:
What is the Kinetic Energy of a 20,000 kg freight car moving at 25
m/s?
KE = ½ mv2
KE = ½ (20,000) (25 m/s)2
KE = 6,250,000 J
Example #7:
What is the Kinetic Energy of a 0.04 g BB traveling 200 m/s?
KE = ½ mv2
KE = ½ (.00004 kg) (200 m/s)2
KE = 0.8 J
Example #8
Calculate the mass of a truck with 81,000 J of KE if its speed is 14
m/s.
m = 826.53 kg