Transcript energyx

Energy
Chapter 11
p.285 - 301
11.1 – Forms of energy
Energy is defined as the ability to do work.
• Heat energy (movement of molecules)
▫ It is the sum of the kinetic energy of an object's molecules.
• Electrical energy (movement of electrons)
▫ That is kinetic energy. The voltage in an electrical circuit is the
potential energy that can start electrons moving. Electrical forces
cause the movement to occur.
• Chemical energy (potential energy until the chemical
reaction puts atoms and molecules in motion)
▫ Heat energy (KE) is often the result of a chemical reaction.
• Light energy (movement of waves and/or light particles
called photons)
▫ It is usually formed when atoms gain so much kinetic energy from
being heated that they give off radiation. This is often from
electrons jumping orbits and emitting moving photons.
• Nuclear energy (internal forces in the nucleus)
▫ When that potential energy is released, the result is kinetic energy
in the form of rapidly moving particles, heat and radiation.
Kinetic vs Potential
• There are many different forms of energy, but
the two main types are kinetic (energy of
motion) and potential (energy of position)
• KE = ½ m v2
• PE = m g h (h is height, in meters)
• All previous forms of energy can be separated or
defined by potential and kinetic energy.
Practice
• P.287 #1-3
• P.291 #4-8
• 11.1 section review #10-13
11.2 Conservation of Energy
• In a closed, isolated system energy can be
neither created nor destroyed.
• Energy of a system = PE + KE
KE = PE
• Read on p.294 about roller coasters, skiing, and
pendulums
• Practice p.297 #15-18
Elastic collisions
• Super-elastic
▫ Kinetic energy is larger after the collision
 Ex. an explosion
• Elastic
▫ Kinetic energy is conserved
 Ex. atomic or nuclear particles with similar charges,
magnets with similar poles facing each other, SuperBall (like ‘Flubber’).
 Ball bearings, a well inflated basketball, or any ball
that bounces some is mostly elastic, but not
completely.
Inelastic collisions
• Inelastic
▫ Kinetic energy is smaller after the collision
 Ex. An under-inflated basketball, or any ball that
doesn't bounce much
• Completely inelastic
▫ Kinetic energy is smaller, and the objects stick
together, after the collision.
 Ex. A block of soft clay dropped onto a hard floor, A
bad car accident where the cars stick together, Two
train cars collide and stick together.
Energy vs Momentum
• MOMENTUM IS ALWAYS CONSERVED
• Energy is only conserved in an elastic collision.
• When working problems, if the collision is
inelastic, SOLVE USING MOMENTUM.
▫ If energy is not conserved, there will be less energy
after the collision than before.
• If the collision is elastic, you may use kinetic
energy to solve.
Practice
• P.300 #19-21
• 11.2 Section review #24-28
Assignment
• Complete the second section of your Work,
Power, and Energy worksheet
▫ (Kinetic Energy and Potential Energy; #1-29)
Chapter Reviews
• Chapter 10 review
▫ P.278-282 (#34-70 even, 79-85 all)
 Extra credit: #89-93
• Chapter 11 review
▫ P.306-309 (#30, 33-41 all, 54-82 even)
• Due by the end of class Thursday 3/17
• Test will be Monday 3/21