Viscosity

Viscosity in Liquids Why do some liquids flow more slowly than others? (oil vs water) Because some particles can move around , but it may be difficult for them to pass by each other Remember: cocktail party analogy!

Viscosity can be defined as the resistance to flow Ie. Water flows easier than oil because water particles slip past each other more easily than oil particles do past one another – stronger bonds between oil particles!! So: oil has higher resistance to flow = higher viscosity

Temperature Effects So, ↑ Temp = ↓forces between particles ↓forces = less resistance to flow = higher flow rate = lower viscosity

Temperature Effects (cont) ↓ Temp = ↑forces between particles ↑forces = more resistance to flow = lower flow rate = higher viscosity

Gases In gases, particles are so far apart and attractive forces are very low So, particles of gas are more likely to collide than rub up against one another! How can the internal friction of a gas be affected?

When a constricted gas flows, it moves in one direction ie. Air flowing out of a balloon or air out of a tire If the gas particles have low enough energy so that most are moving in the same direction, then the viscosity will be low…

But, as the particles gain energy, the motion increases in all directions, which increases the number of collisions. Therefore, internal friction is increased and it won’t flow as well.

Temperature Effects So, as the temperature increases, gas particles gain energy and move faster and the number of collisions increases ↑ Temp = ↑ viscosity ↓ Temp = ↓ viscosity (The exact opposite of liquids!!!!)