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Skill 8 of 14
In Progress

# Sign conventions

Which of these is the correct energy conservation law:1

$$\unicode{x24b6} \quad E_1+Q+W=E_2\qquad\qquad\unicode{x24b7} \quad E_1-Q+W=E_2$$
$$\unicode{x24b8} \quad E_1+Q-W=E_2\qquad\qquad \unicode{x24b9} \quad E_1-Q-W=E_2$$

they all are! Or, they all might be.

Do you remember Newton’s 2nd law where forces were summed up? Do you remember how we couldn’t know which forces to give which sign before first having chosen a direction to mean ‘positive’?2 It seems we have a similar issue here with energies.

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