Momentum and Impulse

Quick
Pressure is defined as force per unit area. Pressure applies to fluids whereas stress, of the same units, applies to solids.


Details
The method of impulse and momentum can be used to solve problems involving force, mass, velocity, and time. Consider a particle of constant mass m. Because:


a
=
d

v
dt

Newton's second law for this particle can be written as:

(Eq1)    
Σ

F
= m
d

v
dt
  =  
d
dt
(m

v
)

The mass m can be taken inside the derivative because it is constant. Thus Newton's second law says that the net force Σ

F
acting on a particle equals the time rate of change of the combination m

v
, the product of the particle's mass and velocity. This combination is called the momentum, or more specifically the linear momentum, of the particle. Denoting

p
as the symbol for momentum the for momentum is defined as:

(Eq2)    

p
= m

v


Momentum is a vector quantity that has a magnitude (mv) and a direction (the same as the velocity vector

v
). The units of the magnitude of momentum are units of mass times speed. The SI units of momentum are kgm/s. The plural of momentum is "momenta."