# Pressure difference when height changes

1. Apr 7, 2013

### FollowTheFez

1. The problem statement, all variables and given/known data

Calculate the difference in pressure (in atmospheres) that the blood vessels in a giraffe's head have to accommodate as the head is lowered from a full upright position to ground level for a drink. The height of an average giraffe is about 6m.
(Note I'm currently only looking for the answer is Pascals)

2. Relevant equations

I thought the equation was P=Po + pgh
but the answer just says P=pgh

Po= 101000Pa

3. The attempt at a solution

P=Po + pgh
P=101000 + (1.05x10^3 kg/m^3) x 9.8 x 6m
P=162.740Pa

ΔP=pgΔh
$\frac{ΔP}{Po}$ = $\frac{pgΔh}{Po}$
= $\frac{(1.05\times103)\times9.8\times6}{1.013\times105}$
=0.609Pa

I don't understand why they've rearranged the equation the way they have and exactly how they are using it. It just doesn't seem right.

2. Apr 7, 2013

### barryj

I thought the equation was P=Po + pgh

I don't think so. this is the equation for absolute pressure.
The problem asks for difference in pressure.