Physics Concepts: Impulse, Momentum, and Force, Slides of Physics

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Impulse

Storm Damage 

A house takes damage from the force of a 60 mphgale-force wind. If the house is subject to a hurricaneat 120 mph the force on the house is

-^

A) Equal.

-^

B) Two times stronger.

-^

C) Four times stronger.

-^

D) Eight times stronger.

Applying Force 

Newton’s law uses mass andacceleration.



Acceleration is the time rateof change of velocity.



If the mass is constant theforce depends onmomentum.

a

m

F

^

v^ t

m

F

p^ t

vm t

F

^

Change in Momentum 

A force acting during a timechanges momentum.



The change in momentum iscalled the impulse (

J ).

J p p p t F

p t

F

i

f















     

  

Nonzero Force 

When momentum changes in a system, an externalforce has acted.

-^

Constant force like gravity

-^

Position-dependent force like the elastic force

-^

Time-dependent force during brief contactbefore

after

pi

pf

F (

t )

Force of Collision



Collisions seeminstantaneous.



They actually take placeduring a short time span.



The force (an elastic force)greatly increases during thecontact, then decreases.

Average Force



The average force is theconstant force that gives thesame impulse in the sametime.



Impulse = area under forcevs. time curve

J^ t

F

av

 





p

p

p

t

F

J^

i

f

^

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Brief Time 

Breaking an object benefitsfrom a short time interval.



The average force ishundreds of times largerthan the weight.

next

 t

y^

/^ v

av

y^

v /2)

= (0.006 m) / (2.5 m/s)= 2.4 ms

Fav

J

/^

 t^ =

3.5 kg m/s)/(0.0024 s)= 1.5 kN