Viscosity

Question 1

Definition of viscosity

Answer 1

How easily a substance flows

Question 2

If a substance has a lower viscosity…?

Answer 2

It flows easier

Question 3

What does stokes law describe

Answer 3

How to calculate viscous drag on a spherical object

Question 4

What are the components of stokes law?

Answer 4

6pi r= volume of sphere
n= coefficient of viscosity (Nsm^-2)
v= speed of ball

Question 5

Why can we ignore drag and not viscous drag in the falling ball viscometer experiment?

Answer 5

For smaller objects the drag force is much smaller than the viscous drag and so can be ignored

Question 6

What forces act on a ball falling through a liquid?

Answer 6

Up: upthrust
Viscous drag
Down: weight

Question 7

If a ball is falling through a liquid at terminal velocity, give the general equation for its forces

Answer 7

Weight- upthrust-viscous drag=0

Mg- pvg- 6pirnv=0

Question 8

What is Archimedes principle?

Answer 8

Describes upthrust: “when a body is partially of totally immersed in a fluid, the upthrust is equal to the weight of the fluid it displaces”

Question 9

Give the equation for upthrust

Answer 9

U=pvg
Upthrust= density of fluid displaced x volume of fluid displaced x gravity

V is equal to the amount of fluid displaced. If the object is partially submerged, V doesn’t equal the balls volume

Question 10

Describe how an object falling through a fluid reaches terminal velocity

Answer 10

When an object falls, it first accelerates downwards due to its weight- upthrust. As speed increases, drag increases so match weight-upthrust. So resultant downwards force decreases, until the net downwards force=0. This is terminal velocity