Force, Mass and Momentum

Newton’s Second Law: F = ma 1 newton = 1 kg ∙ 1 m/s² Force: 1 pound = 4.45 newtons Your weight is the force of gravity: F = mg g = 10 N/kg 225 pounds = 1000 newtons

Momentum = p = mv Units: p = mv Units: kg ∙ m/s Newton’s First Law : An object in motion continues in motion If there are no forces, velocity doesn’t change Δv= 0 momentum doesn’t change Δp = 0 Δ = delta = difference = change F = ma = mΔv/ t = m(v f – v o )/t = (mv f – mv o )/t = (p f – p o )/t = Δp / t F = Δp / t The rate of change of momentum equals force.

Impulse F = Δp / t The rate of change of momentum equals force. If we mulitply by t F ∙ t = Δp Ft is called impulse (F ∙ s = work = Δ Energy) Impulse = Change in Momentum newton ∙ second = kg ∙ m / s (1 newton = 1 kg ∙ 1 m/s²)

The Third Law Newton’s Third Law: “If A pushes B then B pushes A” (in opposite directions) F A = −F B Time is equal t ∙ F A = − t ∙ F B The impulse is equal and opposite Δp A = − Δp B Δp A + Δp B = 0 Momentum is conserved

Conservation Energy is Conserved Momentum is Conserved Mass is Conserved