ABCDEFGHIJKLMNOPQRSTUVWXYZ
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Gravitational ForceElectric Force
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Works onmass charge
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Direction of forceAlways attractsAttract or repel
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Force on a test mass or chargeFg = mg Fe = qE
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Force between point objectsFg= GMm / r^2 Fe = kQq / r^2
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deduced, and then confirmed by experiment
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Field strength (by defintion)g = Fg / mE = Fe / q
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force per unit mass or charge in field
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Unit of field strengthN / kg (also = m / s^2 )
N / C (also = V / m, useful for field between plates)
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Field strength around point objectg = GM / r^2 E = kQ / r^2
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(combine equations above)
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Potential energy between two point objectsEp = -GMm/r
Ep = kQq/r (if one charge is negative then this will come out negative and it will look just like gravity)
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(found by integrating F*d (work) from infinity to r)
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Unit of Potential EnergyJJ
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Gravitational or Electric Potential (by defintion)Vgrav = Ep/mVelec = Ep/q
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work per unit mass or charge to bring from infinity to a point in the field
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Unit of potentialJ / kg1 volt = 1 Joule / coulomb
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Gravitational or Electric Potential around point object
Vgrav = -GM/rVelec = kQ/r
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(combine equations above)
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Change in potential energyW = m*𝚫(Vgrav). (in calculus this is m*dV)
W = q*𝚫(Velec) (in calculus terms, q*dV)
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(rearrange definition of potential)in a uniform g field this becomes mg𝚫hin a uniform g field this becomes qEd
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Relation between field strength and potential|g| = dV/dr |E| = dV/dr
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the field is the slope of the potential
the field is the slope of the potential
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