Transcript The Law of Conservation of Energy

Conservation of
Energy
 How did you get to school today?
 If you walked, did you get tired? Why
do you think you got tired?
 If you rode in a vehicle, did the
vehicle ever just shut down and stop
for no reason?
Energy
You were able to travel this
morning because of Energy.
This is the ability or capacity of any
physical system to do Work.
All work is done by Energy. Since
there are so many different kinds
of forces, energy often takes on
many different forms.
Two BASIC Forms of Energy
There are two basic forms of energy:
Kinetic Energy and Potential Energy.
2 Basic Forms of Energy
All types of energy fall under
these two categories
(forms).
Kinetic Energy are forms of
energy in motion
Potential Energy are forms
of energy that are stored.
Mechanical Energy
 Mechanical energy is due
to the position and motion
of the object.
 What happens to the
mechanical energy of an
apple as it falls from a
tree?
Energy Changes
 As the apple falls to the ground, its height
decreases. Therefore, its GPE
decreases.
 The potential energy is not lost… it is
converted into kinetic energy as the
velocity of the apple increases.
 What happens to the mechanical
energy?
Mechanical Energy
The energy in the system remains constant
– the same!!
Swinging Along
 Think about the changes in energy when
you are on a swing…
 At what point do you have the most
potential energy?
 At what point do you have the most
kinetic energy?
 What happens to the mechanical
energy?
 But how? If I stop pumping while I’m
swinging, I stop!! So, where’s the
energy?
Mechanical Energy
The energy in the system remains constant
– the same!!
Energy Changes
 You need to remember friction…
 As you slow down on the swing, the
hooks and the chain rub against each
other and air pushes against the rider.
 Friction causes some of the
mechanical energy of the swing
to change to thermal energy.
 Thermal Energy or heat, is
the kinetic energy of
particles of matter.
Thermal Energy
 It is the heat caused by the friction of the
molecules moving fast and bumping into
each other. That’s why it is kinetic
Changing Forms of Energy
 Energy is most noticeable as it
transforms from one type to another.
 Electrical energy comes from the
movement of electrons.
 Do you think electricity is potential or
kinetic energy?
Kinetic!
Examples of Electric Energy
Converting to another kind
of Energy
 Radio electric to sound energy
 Lightbulb, electric to light or thermal energy
 Hair dryer, electric to thermal energy
Changing forms of Energy
 Chemical Energy is the
energy that holds bonds
between atoms together. This
is potential because you don’t
get the energy until you break
the bonds.
Chemical Energy
An example of transforming chemical
energy is a car engine. Chemical
potential energy in gasoline is
transformed into kinetic energy of
the car as it moves
Energy in Your Body
 Even the energy converted in your body
follows the law of conservation of energy.
 Chemical potential energy is transferred
to kinetic energy that allows your body to
move!!
Mechanical Energy
The energy in the system remains
constant!!
KE and PE
 In many situations, there is a conversion
between potential and kinetic energy.
 The total amount of potential and kinetic
energy in a system is called the
mechanical energy
 Mechanical energy = PE + KE
The Law of Conservation
of Energy
 The Law of Conservation of Energy
states that energy cannot be created
or destroyed. It can only be
transformed!
 The big picture… the total energy in the
universe remains constant.
Conservation of Energy
 Energy is transformed… not destroyed!!