Transcript energy - St. Joseph School

Potential and
Kinetic
Energy
Explore Activity
Page 123
What is energy?
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When an object is able to change it’s
environment, we say the object has energy.
The use of energy involves change
Forms
- radiant, electrical, chemical, thermal and
nuclear
ENERGY = the ability to cause a change
How is all energy divided?
All Energy
Potential
Energy
Kinetic
Energy
What is Potential Energy?
o Energy that is stored and
waiting to be used later
o Explain how this flower
pot has potential energy.
What is Kinetic Energy?
o Energy in the form of motion
o The greater the mass of a
moving object, the more K.E.
o The greater an objects velocity
the more
K.E.
WORK
• = The transfer of energy through
motion.
• In order for work to take place, a
force must be exerted through a
distance.
Calculating Work
• When a force acts over a distance in
the direction of an object’s motion,
the work done can be calculated as
• work = Force x Distance
•W = F x d
Calculating Work
• Which would require more work?
Lifting a pack of gum from the floor to
waist level or lifting a pile of books
through the same distance?
• The amount of work done depends
on
• Amount of force exerted
• Distance over which force is applied
When is Work Being Done?
•Something has to be moving
•The motion must be in the
same direction as the applied
force.
Conservation of Energy
Think about swinging
on a swing.
How does the
energy during these
movements
change?
Mechanical Energy
•The total amount of kinetic
and potential energy in a
system
Law of Conservation of Energy
• Energy may change from one form to
another, but the total amount of energy
stays the same.
• The Law of Conservation of Energy states
that energy may change form but it cannot
be created or destroyed under ordinary
conditions.
The Mechanical Energy is not Lost
• Will the swing go back and forth
forever?
• Why?
• Where does the energy go?
The Human Body
• What forms of energy are in the
human body?
• With your left hand, reach your right
shoulder.
• We just converted
________________ energy in our
bodies into ________________
energy in our arms.
Balancing Energy Within our
Bodies
• In our bodies, stored energy (that
found in fat) is lost when work is done
or heat is lost by your surroundings.
• To maintain healthy weight, you must
have proper balance between energy
taken in and energy lost from your
body as work or heat.
Food  Our Chemical
Potential Energy
Think about what you ate this morning.
Your body has been chemically
changing your food into molecules that
can combine with oxygen and be used
as fuel.
Even if you didn’t eat breakfats, the
stored fat in your body is converted to
energy.
Measuring Food Energy
• CALORIE
• = 4,180 joules
• Every gram of fat a person consumes
can supply 9 Calories of energy.
• Carbohydrates and proteins supply
about 4 Calories of energy per gram.
Why do our bodies need an
energy supply?