0
   

Momentum and kinetic energy.

 
 
Reply Wed 8 Mar, 2006 01:01 pm
  • Topic Stats
  • Top Replies
  • Link to this Topic
Type: Discussion • Score: 0 • Views: 5,979 • Replies: 7
No top replies

 
fresco
 
  1  
Reply Wed 8 Mar, 2006 01:20 pm
Force=Rate of change of momentum
= (mv-mu)/t = ma

Energy(= Work) =Force x distance moved

If distance is s then v(sqd)=u(sqd) + 2as
so if u=0, s= v(sqd)/2a

Placing this in the energy expression
Energy = ma x s = ma x v(sqd)/2a = 1/2 mv(sqd)
0 Replies
 
markr
 
  1  
Reply Wed 8 Mar, 2006 01:20 pm
Neither.

force = mass x acceleration

But, energy and momentum are conserved.
0 Replies
 
fresco
 
  1  
Reply Wed 8 Mar, 2006 01:24 pm
We should add of course that

momentum = mass x velocity
0 Replies
 
coluber2001
 
  1  
Reply Wed 8 Mar, 2006 01:49 pm
Yes, but if I fall and my head hits the ground, is it hitting it as Mass x velocity or 1/2 mass x velocity squared? If a bat hits a ball is it hitting it with the force of momentum or kinetic energy? Isn't kinetic energy 1/2mass x velocity squared?
fresco
 
  1  
Reply Wed 8 Mar, 2006 02:02 pm
Coluber,

Your question is imprecise.

Your head is hitting the ground with

a velocity v
a momentum mv
a force mg (if you fall)
an energy 1/2 mv(sqd)

each of these are dfferent physical combinations in terms of their reducibility to products of the three basic entitities MASS, LENGTH & TIME
0 Replies
 
DrewDad
 
  1  
Reply Wed 8 Mar, 2006 02:12 pm
Energy and momentum are two separate things (if I recall my physics correctly).

In any system, total momentum and total energy will remain constant. But you calculate each separately.

In your example of your head hitting the ground, your head has a certain momentum and a certain kinetic energy.

When your head hits, some momentum will be transferred to the earth. Some kinentic energy will be transferred as well, but some kinetic energy will also be converted to heat (from friction), sound waves, etc.
0 Replies
 
justinquintos
 
  1  
Reply Mon 5 Jan, 2009 10:30 am
@coluber2001,
if you fall,
a force will hit you equal to 0 - (ur initial momentum) all over the length of time it takes for your momentum to be zero..

work is change in kinetic energy,, so the earth does work on you (negative work)
the distance required to decelerate you to a stop is almost zero coz it's instantaneous.

so the force that will hit you is work/distance... since the distance is very small, the force is large, that explains why it hurts (if you fall at high velocitie)..
0 Replies
 
 

Related Topics

Evolution 101 - Discussion by gungasnake
Typing Equations on a PC - Discussion by Brandon9000
The Future of Artificial Intelligence - Discussion by Brandon9000
The well known Mind vs Brain. - Discussion by crayon851
Scientists Offer Proof of 'Dark Matter' - Discussion by oralloy
Blue Saturn - Discussion by oralloy
Bald Eagle-DDT Myth Still Flying High - Discussion by gungasnake
DDT: A Weapon of Mass Survival - Discussion by gungasnake
 
  1. Forums
  2. » Momentum and kinetic energy.
Copyright © 2022 MadLab, LLC :: Terms of Service :: Privacy Policy :: Page generated in 0.03 seconds on 06/25/2022 at 02:35:00