Newton II
Force, Acceleration, and Impulse
Force = rate of change of momentum
F
mv
t
Initial velocity u (m/s); final velocity v (m/s); mass m (kg); Force F (N); time t (s)
mv  mu
This is final Velocity () – initial () velocity. (Strictly
t
speaking momentum)
1. F 
2. F 
m(v  u )
vu
but
 acceleration (a) ()
t
t
3. So F = ma (Newton II) ()
Impulse
Impulse is the change in momentum
Impulse = mv – mu ()
From equation (3) we can say that:
Impulse = F × t ()
Units for impulse are Newton seconds (Ns) ()
Graphs
Impulse is the area under the force – time graph. Sketch force time graphs for:
(b) a passenger of mass 100 kg
with no restraint, hitting the
dashboard. t = 0.1 s ()
Force (N)
Force (N)
(a) a passenger of mass 100 kg
wearing a seatbelt and restrained by
an airbag. t = 0.5 s ()
Time (s)
Time (s)
11 marks