OK, here's the story....

I'm driving to work and I see this old lady driving a Lincoln Town Car @ 70mph with one of them little 5-6 pound yapping dogs on the rear package shelf. So I get to thinking about what would happen if the lady all of the sudden stopped short or had a head on collision.

Now obviously the dog would become a projectile. My question for the physics guy's is this....At what speed would the little yapping dog hit the lady in the back of the head, and at how many foot pounds of energy?

The dog could also splat on the windshield, but that wouldn't be as funny as it hitting the idiot lady in the back of the head.

That would be 70mph, of course. The car would come to a complete stop in a foot or two at most, while the dog will continue to go 70mph until it hits something.

Energy of a 5lb dog at 70mph is...
819ft*lb
for reference, a 55g bullet at 3200fps is...
1250ft*lb

However, dogs don't penetrate very well.
[:D]

There are a few things you need to take into account...

Assume these things:
#1 The lady is going 70 mph, and STOPS INSTANTLY (No decelleration. No car crumbling, INSTANT STOPPAGE.)

#2 The little dog is on a frictionless surface. The ONLY thing that kept the little dog there was the back window during acceleration.

#3 There is NOTHING in the path of travel btw the little dog and her head.

Now that we have eliminated variables that I cannot judge, we can go on.

Force=mass x acceleration
F=6lbs x 102.6 ft/sec (70 mph in more usable terms...)

[b]Force of puppy = 615 foot pounds per second.[/b]

Now, IN THE REAL WORLD, she would actually slow down (car crumbling prior to stopping), the puppy would lose some launch speed (from the friction of the back deck), and her headreset would absorb SOME of the blast...

..Her a$$ would STILL be $ucking the proverbial canal water.

The dog has more knock-down power because it weighs more. Unfortunately, loading 8 dogs into a magazine is kinda tricky.

Am I a smartass or what?

I get more knock down from my dog-cannon: I have preban FULL capacity mags!

P=mv
5 lb dog @ 70 mph = somebody do this conversion for me i'm in florida on winter break...

Completed 4 minutes earlier... .Where's my cookie?

I knew I could count on you guy's!! [:D]

Of course, after the old lady hits the steering wheel at 70 mph herself, the only thing the doggie is going to hit is a dead old lady.

Umm... ft/sec is velocity, not acceleration. What you have there is impulse.

Didn't I say I was a smartass?
[;D]

Kinetic Energy = .5 m*v^2

Wait a sec...

KE = .5*m*v^2

m = 5lbs = 2.268kg
v = 70miles/hr = 32.29 meters/s

KE = 1110.44 Joules(kg*m^2/s^2) of energy (not force) = 819 ft*lbf

Ignoring all the same stuff as before.

OK, now I, the person guilty of spewing untruth out of my mouth regarding this question, am totally confused!

Funny you should mention that.
I had a pair of 7 pound speaker boxes mounted to the rear package shelf thingie once. One of them hit the headrest of my driver's seat hard enough to crumble when the car decellerated from 75mph down to 0 within a split second.
Hate the thought of what that thing would have done to my head.

(No, I didn't hit the steering wheel, but getting stopped by the seatbelt wasn't exactly pleasant either.)

Man, I can see the entire Mars Orbiter Team belongs to ar15.com [:D]

Do a little units analysis, guys.

OK, I am still confused,

"poodle drop compensation"...

I think this will redeem me!

Acceleration = change in speed/change in time.

ASSUME IT TAKES 1 SECOND TO GO FROM 70 MPH TO ZERO MPH.

Therefore:
Assuming all previous assumptions EXCEPT FOR THE INSTANTANEOUS STOP!

70 mph = 102 ft/sec

Acceleration= (102.6ft per sec - 0 ft per sec)/(1sec - 0 sec)

Acceleration = 102 ft/sec²

Force = Mass x acceleration
F= 6 lb poodle x 102.6 ft/sec²
Force of poodle = 615.6 ft/sec²

Therefore, in ONE second, that poodle will impart 615 foot pounds of force on the back of the lady's skull!

Mace, thank you for not letting my error "carry forward"!

6 lbs is NOT mass, that is WEIGHT.  

You need to convert the 6 lbs to SLUGS to get the mass. (divide by 32 ft/s^2)

Doh! I get it now!

mass= 6lbs/(32ft/sec²)
mass= 0.1875 lb sec²/ft

NOW, go back to what I worked out earlier...

70 mph = 102 ft/sec

Acceleration= (102.6ft per sec - 0 ft per sec)/(1sec - 0 sec)

Acceleration = 102 ft/sec²

Force = Mass x acceleration
F= 0.1875 lb sec²/ft x 102.6 ft/sec²
Force of poodle = 19.23 lb   ???

NOW I'm confused again! The units don't make sense!

Holy Crap!! Now I am totally confused. All of these number, formula thingies are making my head spin (did I mention that I used to cut out of high school......a LOT!).

So is it 600+ lbs.ft. or 800+ lbs.ft.?

Oh, and BTW, it wasn't one of those stupid Poodles, it was one of them thar' tiny Terrier yapping models [:)]

I am trying to figure out if the yapping mutt would slap that dumb ass lady upside the head as hard as a sledehammer[:D], explode upon impact, thereby knocking her head up against the steering wheel, thereby causing her dentures to come flying out of her face, thereby causing said dentures to imbed themselves into the windshield, thereby causing the first emergency responders on the scene to say WTF???? [}:D]

Wind resistance/drag of short hair vs long hair?

lbs = (slug)(feet)/(sec^2)

I always loved the term "Slugfeet" in physics......

BTW this is the precise reason why we should switch to metric.  IT is alot easier to work with.

Lbs are newtons in SI units. In other words units of FORCE.

Slugs are KGs in SI units. Units of mass.

Now you need to convert force to energy to figure out how many 'foot lbs' is exerted.

BigAL and Mugzilla are correct. The ENERGY is 820 ft-lb, and the FORCE is 19 lb. However, this is an impulse-momentum problem, and connot be solved without knowing the real acceleration. This must be determined by experimentation.

I REPEAT: THIS MUST BE DETERMINED BY EXPERIMENTATION!

Now let's see how many PETA trolls pop out of the woodwork!

BTW - ColKlink's diagram and method is terrific, but his velocity unit is wrong. Change to ft/sec and you'll get the correct answer. He gets full credit, though, for the wonderful free body diagram!

[img]http://wtf.rotten.com/wtf/wtf.01/ling.jpg[/img]

if the car hit and suddenly stopped at the exact middle of a dog yap (dog's mouth open), it would have significantly slowed down his acceleration (wind/air resistance) to render all you guys' figures wrong.  

i suggest when the experiment is carried out, to duct tape the little bastard's snout shut to avoid this phenomena. it would also help the little old lady concentrate on getting her head on collision done right.

if i can offer any more advice, please feel free to IM me.

m=.1875 slugs
v=102.7ft/s
k=.5mv^2
.5*.1875*102.7^2=988.808 lb ft

This is correct

I can't stand ot any longer...

70 mi/hr = 188,160 furlongs/fortnight

5 lbs = 48.77 bus tokens = 0.0052 shitloads

0.0052 shitloads traveling at 188,160 furlongs/fortnight = 3752.0 tyson-bites/punch.

Got it? [:D]

Now you have to divide that energy over the cross section of the dog's impact surface.

This will significantly reduce the energy delivered to any one point on the lady's head.

The .45acp round delivers a similar amount of energy but it is in the form of a point load.

OK, I'll try this again. (I had a revelation..)

Lets assume the dog is 6 POUNDS OF MASS. (lbm)

In other words, it can be said in 2 ways:

6 lbm

OR

6 sec²lb/ft (I replaced LBM with sec² lb/ft) If you divide by 32 also, you change it to slugs!!! SLUGS don't fit in the equation. (It would be akin to multiplying 4 by 2 dozen and getting 8.)

THEREFORE,

F=m*a
F= (6 sec²lb/ft) X (102.6 ft/sec²)


Force = 615.6 POUNDS OF FORCE (lbf)


NOW, why do I think this way? If you do a conversion, the answer is WAY TOO LOW! Poodles have much better ballistic properties, and have to be higher than 19 lbf. 615 lbf is much more like it.

I don't see the need for the conversion. Doing the conversion enables you to express it in SLUGS.

Here is a way to think of a slug: You can say TWELVE bullets, or you can say ONE DOZEN bullets....

I DO, however, see the need to express mass in sec²lb/ft. My previous answers didn't even end up in the correct UNITS! What the UNITS at the end should be is POUNDS OF FORCE (lbf). No more, no less.

My brain is full. Can I go home now?

I used to teach physics so I should know this, but logically speaking, why is the velocity squared?  I can derive the equations using calculus, but I can't explain, for example, to my 14 year-old great-niece why that term is squared.  I showed her a graph of the acceleration of an object graphed as time versus velocity.  The current velocity at any point in time is simply the y-axis.  The acceleration at any given time is the slope.  The area under the curve ... blah blah blah ... When she asks "why is it squared?" I don't have an answer.  "Because the math says it is" isn't a very satisfying answer.z

I showed this to my dog and asked him how it would feel to hit the driver in the head. He said "ruff."
I asked him what would fly off of the tree she hit. He said "bark".
I asked him what he would bounce off of after he hit the lady. He said "roof".
I asked him what the lady was drinking to make her run into a tree. He said "whine."
I asked him what she skidded in before impact and he said "growellvel."
I asked him what he would say right before impact and he said "oh,shit."

ROTFLMAO!!!  

Try WC872 thats what they are using on the 20mm. Just a guess of 210grs? Hmmmm what about using compressed air? Like a spud gun?

How much energy would be required to launch a 500 pound load of raw ground pork into mecca from Cleveland, Oh? (assuming pork is in a sealed, aerodynamic container set to air burst at approx 500 ft.) Gross weight of container and pork = 500 lbs.

Not sure this is a satisfying answer but from the internet (http://nov55.com/vel.html):

"No mass can move at velocity squared. As a result, the formula for kinetic energy (KE=½mv²) is an abstraction apart from the motion of the mass.

--------------------------------------------------------------------------------
This claim is not obvious to a lot of persons, and it proves nothing in itself. But the mathematical proof of the error shows that this statement is correct.

The statement says nothing about mathematics or the use of abstractions in mathematics. It says how kinetic energy can or cannot be represented.

Kinetic energy is the energy of motion. Motion cannot be represented as velocity squared, because nothing can move at velocity squared. Anyplace else, velocity can be squared when needed.

The distinction here is between a representation and a procedure. Math is a procedure. It can have anything in it which is useful.

The formula for kinetic energy can only produce a correct result when it properly represents kinetic energy. A correct procedure must follow a correct representation of kinetic energy.

What the formula represents is motion. Motion cannot be represented with velocity squared, because motion is defined as velocity nonsquared.

The implication of the erroneous definition of kinetic energy (KE=½mv²) is that energy is not the motion of a mass but an abstraction that goes with it. The logic can be questioned, but my analysis says kinetic energy cannot be an abstraction apart from the motion of the mass, because gallons of fuel are not an abstraction, and fuel has to transform quantitatively into kinetic energy. The two proofs that I use show that there are points of conflict in separating kinetic energy from the motion of the mass."

Confused yet? I guess the answer really is "because the math says it is." Good luck explaining to your niece. [:D]