Download Physics 20 Energy – Elastic Potential Energy - ND

Physics 20 Energy – Elastic Potential Energy Elastic Potential Energy:
Hooke's Law Devices: F = -kx
The amount of restoring force, for a Hooke's Law device, is __________ ______________
to the _________________ from the equilibrium and is in the opposing direction
F is called the __________________force (or elastic force)
k is the __________ _____________. It is a measure of how stretchy the spring is
To find the value of k: The constant can be determined by hanging _____________ from
the spring and seeing how much it stretches. If Fg is graphed as a function of __________
_______________ the slope of the graph will be the ______________ ______________.
Elastic potential energy is stored in such devices as bows, springs, bent poles and bungee
cords. (Anything that is a Hooke's law device with SHM)
These devices gain potential energy when they are ____________ or _________________.
Work to Elastic Potential
(When they are released, they can do work on an object)
To calculate potential energy of spring you cannot use W = Favg x, where x is the amount it
is ______________________ from its normal length because the force is not constant, it
becomes __________________ the more the spring is stretched
Example 1: How much energy is stored in
the trampoline which has a spring constant
of 500 N/m when a child stretches the
trampoline by 25.0 cm?
Simple Harmonic Motion (SHM)
Motion that repeats itself in a _____________ ________________ over the same path.
Simple harmonic motion begins when an object is in ____________________ and is
disturbed by an ______________________ force. A force pushes the object out of
equilibrium. The object is then set into a pattern in which it _________________
around the equilibrium position.
Pattern of SHM:
Ek
v
Fr
a
x
Ee
1 S Molesky @ Notre Dame Physics 20 Energy – Elastic Potential Energy Example 2: A mass of 40.0 g is placed at the end of a spring with
spring constant 400 N/m which is then stretched a distance of
4.50 cm. What velocity will the mass have when it:
a) is at maximal displacement?
b) moves through the equilibrium position?
Bungee Jump: A bungee jump shows an example of elastic
potential, gravitational potential and kinetic energy in action.
The jumper begins with gravitational potential energy. Elastic
potential energy begins to be stored when the jumper starts to
stretch out the bungee. The jumper oscillates around an
equilibrium position (in which Fg = Fr ) and ends up at the
equilibrium position.
Closure:
a) What is the name of the law that describes how a spring
works?
b) What factors determine how much energy is stored in a spring?
c) How do the Law of Conservation of Energy apply to springs as
they oscillate?
2 S Molesky @ Notre Dame