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and Work
What is energy?
•Ability to make something
happen
•Or work to happen
Potential and Kinetic Energy
• Potential energy is energy that is
stored in an object.
• Kinetic energy is energy of motion.
Potential energy
• Potential energy (P.E.) is the ability
of an object to do work because of
its position. work done by the object
= P.E. lost
• work done on the object = P.E.
gained.
Potential energy
•
Potential energy is a type of energy
that is "hidden" in some way. It is a
type of energy that can be
converted to other forms and often
is related to some attractive or
pushing forces.
Types
• Elastic Potential Energy
– Anything that can act like a spring or a
rubber band can have elastic potential
energy.
– Let's take the rubber band or a spring
– Wind up toys store energy this way
Gravitational Potential
Energy
• There is a constant attractive force
between the Earth and everything
surrounding it, due to gravity.
• To lift something off the ground it takes
energy, so just by lifting an object, that
object now has higher gravitational
potential energy.
• Gravitational potential energy is typically
converted into kinetic energy (an object
falling) before it is converted into any
other type of energy.
• Hydroelectric power is generated this way.
As the water falls, it turns a turbine, which
pushes electrons around, creating an
Changing GPE
• What does it depend on?
Chemical Potential Energy
• A chemical bond can be thought of as an
attractive force between atoms.
• Because of this, atoms and molecules can have
chemical potential energy.
• Anytime two atoms form a strong covalent or
ionic bond or two molecules form a chemical
energy is converted into other forms of energy,
usually in the form of heat and light.
• Strong bonds have low chemical
energy and weak bonds have high
chemical energy.
Kinetic energy is the energy
of motion.
• Any object that is moving has kinetic energy.
• Ball Moving Horizontally
• Kinetic Energy Equation
• m = mass (in kg), v = velocity (in m/s), and KE
= kinetic energy (in J = joules).
• Remember, the units for energy are
Joules - Kilogram . meters / sec2
• Practice Problems:
• 1. A 12 pound bowling ball is held 20
feet above the floor. Calculate its
GPE.
• 2. A 2kg object is traveling at 4m/s.
Calculate its KE.
• Law of Conservation of Matter and
Energy:
the total matter and energy in the
universe is always conserved.
Can energy be changed
into matter?
• Think of matter and energy as
two forms of the same thing that
can be converted from one to
another.
E=mc2
• While it is possible to change matter into
energy and energy into matter, the sum of
the two is always constant.
• Einstein's equation shows this relationship.
• E = Energy (Joules)
• m = mass (kg)
• c = speed of light (300,000 km/s)
• The two most common energy
conversions are:
• Potential energy changing into
kinetic energy.
• Kinetic energy changing into
potential energy
• Mechanical energy= potential energy
+ kinetic energy
• Mechanical is energy due to the
motion of an object
Mechanical energy
Forms of energy
• Mechanical
• Chemical
• Heat
• Electromagnetic
• nuclear
Mechanical energy
• There are two main types of mechanical
energy.
• Motion energy: This is the energy
something has because it is moving
• Stored mechanical energy: This is energy
something has stored in it because of its
height above the ground or because it is
stretched or bent or squeezed
Electrical energy
• The energy that flows through wires
and powers the lights and appliances
in your home.
• The energy is in the form of moving
electrons
Electromagnetic energy
• Visible light or radiant energy
• X rays
• Radio waves
• Microwaves
• This form of energy can travel
through a vacuum
• Concept Understanding:
•
• 1. Assume that all the matter in your body could be
converted into energy, how many Joules of energy would
that be?
• Hint: 1 pound = 0.5 kg
• Show all your work used to solve this problem.
• 2. Give one example of each of the following energy
conversions:
• Chemical energy changing into heat energy.
• Heat energy changing into mechanical energy.
• Nuclear energy changing into heat energy.
• Mechanical energy changing into electromagnetic energy.
Conservation
• Matter can be changed into energy
• Energy can be changed into matter
• Neither can be created or destroyed
Work
• Develop a definition from the activity
Work
• W=force x distance
• W=fxd
• The unit is the newton/meter also
called joule
• Work is force exerted through a
distance
• Complete activity pg 303
Measure work
• To measure work you must measure
the force in the direction of motion
• Complete problems #3, 7, and 8 on
page 303
Power
• Power=work/time
• It is a rate
• The unit is the watt---W or 1 j/s
Analysis and conclusion
• 1 When the mass is released from
the same height with the interrupter,
is the ending height the same as its
starting height? Use your data to
support
• 2 Analyze the energy transfers. At
what point along a single swing does
the mass have the greatest kinetic
energy? The greatest potential
energy
• 3 Do the results support your
hypothesis?
• 4 Compare the starting heights to
the ending heights of the mass. Is
there a pattern? Can you account for
the observed behavior?
• 5 Do your results support the law of
conservation of energy? Why or why
not?
• 6 What would happen if the mass of
the bob was increased?