Investigating Viscosity Changes with Temperature

The viscosity can be calculated by allowing small spherical objects of known weight to fall through a fluid until they reach terminal velocity.The masses of the balls are measured using a balance and the diameters of the balls are measured using Vernier callipersThe density of the balls is calculated using

density ρ

=

mass volume

Three rubber bands around the tube to make three positions. The highest is placed below the surface of the liquid to ensure the ball is travelling at terminal velocity when it reaches this band.The remaining two bands are placed 10 – 15 cm apart so that time can be measured accuratelyRelease the ball and start the timer when it reaches the first band, then find the time to fall the distances d₁ between the highest and middle rubber band and d₂ between the highest and lowest bands.Repeat three times for balls of same diameter at different temperatures.At terminal velocity, the vector sum of the forces on the ball is zero soweight – drag – upthrust = 0From this it can be shown that

η

=

2r2g(ρ - σ) 9v

, where η is the viscosity of the liquidr is the radius of the ballρ is the density of the ballσ is the density of the liquidv is the terminal velocity.