L14 能量 Energy

←	L14 能量 (Mechanical) Energy	→

Key Ideas

Time is not involved in this viewpoint of motion. Before → After
No vectors involved
System & Environment.
- Energy transfers between system and environment (Δ E_sys = W + Q)
- Energy is transformed within a system. (U ↔ K ↔ E_chem ↔ E_th)
Friction (f_k) changes K → E_th (Δ E_th = f_k Δ s)

$$ \Delta E_{sys} \, = \, W $$	$$ K \, = \, {1 \over 2} \, m \vec v \cdot \vec v $$
$$ W = \int \vec F(s) d \vec s $$	W [N m] = [kg m s^-2][m] E [J] = [kg][m/s]² NB: F=f(s) not F=f(t)

F_sp = - k Δs

W = -k/2 (Δ s _f² - Δ s _i²)