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Science 8 Chapters 5 and 6 Please review this powerpoint with your packet to get ready for the post test ENERGY! Energy is the ability to do work. Recall from Chapter 4: work is the force needed to move an object in the direcBon of the force, so energy is the ability to do this! The unit for energy is the Joule, just like for work! Energy is Transferred Energy cannot be created or destroyed, it is TRANSFERRED! So when two hands come together, the energy used to move your hands is converted to sound energy and you hear a clapping noise. Kinetic Energy KineBc energy is the energy of moBon. Things that are moving have kineBc energy. Look at all these examples: And more!!! 6
Calculating Kinetic Energy
A formula to find
the kinetic energy
of any body
based on its
velocity. 7
Potential Energy
• An object
can store
energy as
the result
of its
position.
9
Gravitational Potential Energy
•  GPE is the energy stored in
an object as the result of
its vertical position (i.e., height).
•  Amt. of GPE is dependent on
two variables:
1. the mass
2. the height
Gravitational Potential Energy So (GPE)
the formula for GPE =Weight x height Ex: a ball with weight of 20 N is held 10 m of ground. How much GPE does the ball have? 20N x 10m= 200 J Mechanical Energy Mechanical energy is the total energy of moBon and posiBon of object = KE + PE High PE, low KE à Low PE, high KE à When the ball leaves the jugglers hand t has high KE, transferred from his hand. As it moves up, the KE changes to PE unBl the ball gets to the top. At this point the ball has all PE unBl it begins to fall. As the ball falls, the PE is converted to KE which you can see because it gains speed. The mechanical energy in the object remains the same through the juggling, it just converts between kinetic and potential energy. Energy conversion: energy is transferred from one form to another form. There are more forms of energy: Thermal!
Chemical!
Electrical!
Sound!
Light!
Nuclear!
Thermal Energy • The random moBon, or vibraBon, of atoms in maYer • The faster the atoms vibrate the more heat energy they have Chemical Energy • What holds atoms in molecules together • Can be released by chemical reacBons like burning wood Electrical Energy • The movement of electrons through maYer • Electricity is a form of electrical energy Sound Energy • Vibrates air molecules • The air molecules move Bny bones in your ear • The message of sound then moves to your brain • Can also vibrate objects Light Energy • The energy carried by light • Yes, whenever you are looking at light, you are looking at energy Nuclear Energy • Holds protons and neutrons together in an atom’s nucleus • Powers the sun and nuclear power plants Identify the forms of energy that are being converted: A wound up rubber band: potenBal energy à KineBc energy Pasta gives you fuel to run a marathon: PotenBal energy à kineBc energy Light from the sun becomes sugar in fruit: light energy à PotenBal energy A hair dryer is used to dry your hair: electrical energy à thermal energy n
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En
Conservation of Energy Energy cannot be created or
destroyed…only changed from one
form to another.
The total energy of an isolated
system remains constant (isolated
systems have no external forces
and no mass changes)
ENERGY BEFORE = ENERGY
AFTER
Energy can be
changed from one
form to another, but it
does not disappear.
Energy Conversion
What about a falling object?
What happens when it hits
the ground?
Where did the energy all go?
Energy Conversions of a dropped object
• As it is falling and when the object hits the
ground the energy is converted into other
types of energy such as:
• sound energy (waves), Light Energy
(sparks), thermal energy due to
friction (heat) in the ground and air,
vibrations in the earth (energy
waves.)
• If the object bounces, some energy
is converted momentarily into elastic
potential energy.
Perpetual Motion? Perpetual moBon is the idea that a machine could be invented that could run forever without any addiBonal energy. Is this possible? NO! Check out the link for examples of machines that have come close! hYp://www.youtube.com/watch?v=287qd4uI7-­‐E Temperature vs Heat Temperature Heat •  The measure of the average kineBc energy of the molecules of a substance. •  The faster the molecules are moving, the more kineBc energy they have, thus a higher temperature. •  The transfer of thermal energy between objects at different temperatures. •  When two objects come in contact with each other, energy is transferred from the object with the lower temperature to the object with the higher temperature. Conduction •  Transfer of heat from one substance to another by direct contact. •  A heaBng pad with warm up your muscles by direct contact Convection •  Heat is transferred by the movement of a liquid or gas. •  Water in a pan can get thoroughly heated by convecBon. Radiation •  Heat is transferred though electromagneBc waves. •  Visible light and infrared waves are examples of electromagneBc waves.