Kinetic Energy

Kinetic energy K is the energy a body has due to its motion: K = ½mv².

Scalar quantity, always non-negative. Units: joule (J).

Depends on the reference frame — moving frame sees different v ⇒ different K.

K = p²/(2m), where p = mv. Useful when momentum is known.

Work-energy theorem: W_net = ΔK. Net work changes KE.

Translational KE (linear motion) + Rotational KE = total mechanical KE.

For relativistic speeds: K = (γ − 1)mc². Reduces to ½mv² for v ≪ c.

Energy of motion can be transferred to other forms: heat (friction), elastic PE (spring), gravitational PE (rising), light, sound.