# Calculate Impact Force Of a Truck Hitting a Deer

1. Apr 12, 2010

### Ryanle

Trying to calculate the impact of an 8000 lb. truck moving at a rate of 55mph, hitting a 200 lb deer that is standing still in the middle of the road. Does assuming it is a localized hit make any difference? What i mean is, if the deer was hit from the back, and his 200lb wieght was focused in a 2 foot wide area on the front of the truck. Thanks!

2. Apr 12, 2010

What a cruel question :D

Perhaps it would be best to idealize and use conservation of momentum.

3. Apr 12, 2010

### Ryanle

The reason i am trying to figure it out is for an insurance claim. Not trying to be cruel and evil lol.

4. Apr 12, 2010

### sophiecentaur

The change in momentum is easy to calculate: The speed after impact would have been
55X(8000/8200) mph, assuming the deer sticks to the front of the vehicle. This is probably not too relevant as the brakes would have been applied before - or immediately after the impact.

But the Force involved is less easy. The same change in momentum can be achieved by a range of forces and the times they are applied. It's called Impulse.
Impulse = Force X time
Small force X long time can be the same as large force X short time
I assume you didn't have a timer or video camera running so you can't estimate the time taken for the actual impact. I guess your insurer will be aware that any force estimate you were to give would be very speculative. Perhaps they are waiting for you to make a preposterous claim which they can then reject? Are they, perhaps, implying that you were driving too fast?

There is a lot of data, taken from human collisions, which connects front-end damage to vehices (and humans) by body impact with speed of vehicle. You could, perhaps, conduct your own experiments - using insurance inspectors as your subjects.

5. Apr 12, 2010

### Ryanle

They are insuring me for the body damage on the truck, but there is also damage to my front axle. They are trying to say there is no way that a hitting a deer could crack a weld on the axle, thats why i'm trying to figure out impact forces to prove them wrong(not looking for exact numbers even). I am pretty sure hitting a 200 lb object in the road, me going 50mph or so, is enough impact to do the damage. BTW, i'll be honest, i'm not that good at complicated math, so any help would be greatly appreciated.

6. Apr 12, 2010

### sophiecentaur

I see your problem but I don't think it's soluble theoretically. You need evidence of other documented collisions.
There could be 'off roader' websites / forums with discussions of collision damage. You are clearly not the first person to have hit a large animal in a truck. I remember riding in my Dad's Peugeot 403 across Bodmin Moor when we hit a steer in a patch of fog. It took out the whole of the front end. It was as if we'd hit a tree.
I think your insurer is 'trying it on' so keep posting queries on every 4+4 website you can find . Someone will be able to help, I'm sure, and give you your evidence.
btw, did you get a photo at the crash site?