2. Momentum (Symbol = p) [Unit = kg m/s]
Inertia in motion The Quantity of Motion
Momentum = Mass • Velocity
p = m • v
Newton’s 2nd Law
F = ma a= ∆v = v f − vi
t t
v f − vi
t • F = m( ) •t
t
Ft = mv f − mvi
I = Ft = ∆p = mv − mv Impulse = change in momentum
f i
Impulse (Symbol = I)[Unit = Nsec]
A force in a certain time
Concept: In order to change momentum,
we need a force in a certain amount of time!
3. I = Ft = ∆p = mv − mv f i
Changing Momentum
Difference between hitting
concrete bridge vs. yellow barrels full of pea gravel
Seat belt vs. Air bag
Δp = Ft Δp = Ft
0-mv = F T 0 -mv =
http://www.regentsprep.org/Regents/physics/phys01/impulse/default.htm
Ft
Momentum is a vector, so direction is important!
4. A 4.0 x 104 N rocket is at rest when it fires its thrusters.
If the thrusters put out an average force of 5.0 x 10 3 N
over 20 sec, then
(a) What is the impulse the rocket experiences?
(b) What is the rocket’s final velocity?
(a) Impulse
I=Ft
I = 5000 (20)
I = 100,000 Nsec
(b) v
I = ∆p = mvf – mvi
100,000 = 4080 vf – 4080(0)
vf = 24.5 m/s
![Momentum (Symbol = p) [Unit = kg m/s]
Inertia in motion The Quantity of Motion
Momentum = Mass • Velocity
p = m • v
Newton’s 2nd Law
F = ma a= ∆v = v f − vi
t t
v f − vi
t • F = m( ) •t
t
Ft = mv f − mvi
I = Ft = ∆p = mv − mv Impulse = change in momentum
f i
Impulse (Symbol = I)[Unit = Nsec]
A force in a certain time
Concept: In order to change momentum,
we need a force in a certain amount of time!](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)