Transcript Energy & Its Conservation

There are 2 forms of energy…
Kinetic Energy
Potential Energy
We already know that
Kinetic Energy is the energy
Of motion.
But what if something is
Not moving?
Potential energy is stored
Energy.
One kind of potential energy is
Energy due to its position
On earth.
This is gravitational
Potential energy.
PE = mgh
If Cal lifts a 2 kg textbook from
The floor to a shelf 2.1 m above
The floor. What is the book’s
Potential energy relative to the
Floor? What is the potential energy
Relative to his head if he is
1.65 m tall?
41.2 J
8.82J
Elastic potential energy is the
Potential energy of a
Stretched or compressed spring.
The spring constant (k) is a
Parameter that expresses how
Resistant a spring is to being
Compressed or stretched.
PEelastic = ½ kx2
The staples inside a stapler are
Kept in place with a spring with a
Relaxed length of 0.115m. If the
Spring constant is 51 N/m, how
Much PE is stored when the
Spring is stretched to 0.150m?
0.031 J
Mechanical Energy is the sum
Of kinetic energy and all forms
Of potential energy.
ME = KE + ΣPE
Einstein recognized yet another
Form of potential energy:
Mass Itself!
He said that mass, by its very
Nature, is just one manifestation
Of Energy.
E=
2
mc
The law of conservation of
Energy states that energy cannot
Be created or destroyed, only
Transferred.
MEi = MEf
The law of conservation of
Matter states that matter
Cannot be created not destroyed.
As far as you are allowed to know.
A large chunk of ice with a mass
Of 15 kg falls from a roof 8 m
Above the ground. Find the
Kinetic Energy of the ice when
It reaches the ground. What is
The speed of the ice when it
Reaches the ground?
1180 J
12.5 m/s
An elastic collision is a
Collision in which the total
Momentum and the total kinetic
Energy remain constant.
m1v1i + m2v2i = m1v1f + m2v2f
2
½m1v1i
+
2
½m2v2i
½m1v1f + ½m2v2f
2
=
2
A perfectly inelastic collision is a
Collision in which two objects
Stick together and move with
A common velocity after
Colliding.
In an elastic collision, the kinetic
Energy is slightly decreased.
Usually it is converted to
Thermal and sound energy.