PHYS 1023 Lecture Notes - Lecture 6: Chemical Energy, Food Energy, Neutrino
24 Aug 2016
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Thursday, February 11, 2016
Physics & Human Affairs
Chapter 6: Conservation of Energy
-Energy as Civilizer
•Solar energy (early)
-Grow food > agriculture
-Creates wind > makes sailing ships possible
•Fossil Fuels (coal, oil, natural gas)
-Chemically altered remains of ancient life forms
-Industrial Revolution; coal fueled steam engine
•Faster production
•Unskilled labor
•New industries
-Work and Energy: Defined
•Do work every day
•Use energy every day
•Physics definitions
-Work: bringing about external or internal changes
-Energy: capacity to do work
-Work (Joules)
•Work is done whenever something is pushed or pulled a distance (force)
•Need something doing the work and something have work done on it
-‘A’ does work on ‘B’, if ‘A’ exerts a force on ‘B’ while ‘B’ moves in the direction of
that force
-Must have force and motion to do work
-Work and Force
!1
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Thursday, February 11, 2016
•How much more work to lift one book than to lift 2 of the same book?
-Lifting 2 books is twice the first
-Work is proportional to force
-Work and Distance
•How much more work to push a book 2 meters than 2 meter?
-Pushing 2 m is more work
-Work is proportional to distance
•Work = force x distance = F x d
-Work and Energy
•A moving object has the capacity to do work
•As book falls, it gains speed; just before it hits the floor, it could do work
•Lifting a book
-Given the capacity to do work
-Capacity is stored in the book
-This capacity is energy
•Energy — the capacity to do work
-Gravity and Motion
•Raised object > gravitational energy (GravE)
•Moving object > kinetic energy (KinE)
•As as object falls, its gravitational energy becomes kinetic energy
•This transformation is known as conservation of energy
-Quantitative Energy
•Work to lift something — force x distance
-GravE = weight x height
•Energy — amount of work an object can do (J)
•Book:
!2
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Thursday, February 11, 2016
-Hold as you lower: book does work on hand
-Drop it: GravE > KinE
-Work by a moving object?
•Kinetic energy — energy due to motion
•KinE = 1/2 x (object’s mass) x (object’s speed)^2
•Larger mass > larger energy
•Larger speed > larger energy
-KinE possible without gravity
-Falling Object
•Ignore air resistance:
-GravE before fall (weight x height)
-KinE at end of fall
-Total capacity to do work doesn’t change
•Energy is conserved (no exceptions so far)
-Energy and Work, again
•System — a specific part of the universe that can be though of as separate
•Any system with the capacity to do work is said to have energy
-Energy is the work a system could do
•Work = Energy
-System does work (process)
-System has energy (property)
-Two Forms of Energy
•Kinetic energy — (KinE) due to motion
-Car
-Flying bird
•Gravitational energy — (GravE) due to force of gravity
!3
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