# Poiseuille's law- Radius vs Flow speed

#### IlyaR

5+ Year Member
I was going over the wiki premed cards and couldn't decide whether there was an error or if I'm just not understanding something Should the answer be a exponential, with a curve towards the x axis?

According to the equation,

AV=dP(pi)r^4/constant

V(pi)r^2=dp(pi)r^4/constant

V=dp(r^2)/constant
So...as TBR says...the graph curves towards the axis which displays greater change.

Am I wrong here?

10+ Year Member
just graph y=x^4

#### Odi

Doubling the radius causes an increase in flow rate of 16X

If everything is held constant than Q=r^4

Doubling the radius Q=(2r)^4=16r^4

The flow rate increases 16x as the radius is increased by a factor of 2x. Flow rate is changing more quickly so D is most reflective of this.

What's the answer on the card?

#### IlyaR

5+ Year Member
Doubling the radius causes an increase in flow rate of 16X

If everything is held constant than Q=r^4

Doubling the radius Q=(2r)^4=16r^4

The flow rate increases 16x as the radius is increased by a factor of 2x. Flow rate is changing more quickly so D is most reflective of this.

What's the answer on the card?
Card says d. But what I don't get is why it's bending towards the y axis. R isn't increasing more than v

Last edited:
About the Ads

#### Odi

Card says d. But what I don't get is why it's bending towards the y axis. R isn't increasing more than v

I see what you're saying. If the axes labels are as is than yeah the graph should resemble x=y^4 and curve to the x axis... not y=x^4 as is.

Looks like they labelled their y and x axis wrong.

• 1 user

#### IlyaR

5+ Year Member
I see what you're saying. If the axes labels are as is than yeah the graph should resemble x=y^4 and curve to the x axis... not y=x^4 as is.

Looks like they labelled their y and x axis wrong.
Cool. Just needed someone to confirm my suspicions lol.

About the Ads
This thread is more than 7 years old.

Your message may be considered spam for the following reasons:

1. Your new thread title is very short, and likely is unhelpful.
2. Your reply is very short and likely does not add anything to the thread.
3. Your reply is very long and likely does not add anything to the thread.
4. It is very likely that it does not need any further discussion and thus bumping it serves no purpose.
5. Your message is mostly quotes or spoilers.
6. Your reply has occurred very quickly after a previous reply and likely does not add anything to the thread.
7. This thread is locked.