# ENERGY. Energy Is transferred within a SYSTEM of objects Isn’t a “thing”. Analogy: Wealth.

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ENERGY

Energy Is transferred within a SYSTEM of objects Isn’t a “thing”. Analogy: Wealth

E g -- Gravitational Potential Energy energy due to an object’s change in height above earth (or other celestial body) System: an object and the earth (or other large object). E g is impossible with one object alone. Evidence : Δ height above h = 0 h = 0 meters

E chem --Chemical Potential Energy energy transferred in chemical reactions (transfer of electrons) Evidence: food fuel batteries

E el --Elastic Potential Energy energy stored in a spring or other elastic object Evidence : object is de-formed (and it can re-form)

E k -- Kinetic Energy Evidence: velocity (motion)

E dis --Dissipated Energy ---- Energy transferred to the surrounding environment. Evidence: light, heat, sound; friction

Summary E g E k E chem E el E dis How we know

Mass energy E = mc 2 Converted by nuclear reactions Other Energy we won’t be discussing right away

Electric Energy Stored in an electric field -- due to + and – charges separated from each other Magnetic Energy Stored in a magnetic field - due to North and South poles of a magnet separated from each other, (or from moving charges) Other Energy we won’t be discussing right away (or at all)

Q: How do we show Energy Transfers between objects? Answer: Energy Bar Charts Show Energy distribution at 2 or more instants in time

Examples of Bar Charts to show Conservation of Energy within a system 2010 olympics - aerial skiing (start at 00:43 sec)2010 olympics - aerial skiing

Aerial skiing EgEg EkEk E dis Energy is always dissipated to other objects in the system as time goes on E dis Top (before jump) On ramp In air stopped EgEg EkEk E dis EgEg

worlds tallest bungee jumpworlds tallest bungee jump - start at 1:40

Bungee Jump EgEg E dis EgEg EkEk Top (before jump) In air During stretch of elastic stopped EgEg EkEk E dis E El

What is this story? EgEg EkEk EkEk E dis EgEg

t(s) What is the physical meaning of each SLOPE and AREA? X (m) v (m/s) t(s) a (m/s 2 ) Mass (kg) Fg = weight (N) a (m/s 2 ) ΣF (N) Avg. Velocity Acceleration Slope: jerk Slope: Gravitational Field Strength (N/kg) Mass (N/m/s/s = kg) Area: meaningless Displacement = Δx ΔvΔv Area: meaningless t (S) ΣF (N) meaningless F f (N) F N (N) Impulse μ meaningless

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