Chp 8 – Adhesion, Cohesion, Viscosity
Okay, up to now, we’ve been studying forces and
pressure. To expand our knowledge of forces, it is
important to study how forces act on matter. Water
is an interesting case. Because water molecules are
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_________, they pull on each other. A glass of
water has water particles below in the __________,
but none above. The downward and sideways
pulling force of the water molecules creates
____________________. Tension is a contact force.
In Activity 8-10, you were able to float a paper clip
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on water. Did you notice the edge of the paperclip
in the water? The paperclip was ___________ than
the water (1g/mL), but floated! The only
explanation was that some _________ was holding
the paper clip up. The force that did this was the
surface tension of the water molecules. Adding soap
interfered with the water particles sticking to each
other. This __________________ the
_________________, and the paperclip sunk. Water
particles’ sticking together is an example of
cohesion. Cohesion exists when both particles want
to stick together.
Adhesion is a bit different. Water likes to stick to
glass. The glass is not attracted to the _________.
If only one object has a sticky force, you’re seeing
__________________.
Okay, onto viscosity. Lab 8-8 Flow Rate examined
this concept well. Water ran down the cookie sheet
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very quickly, leading us to conclude that as sticky as it is, water has low _____________.
Viscosity is defined as the resistance of a liquid to flowing. The most viscous material
we tested was __________. Had we tested it, molasses would have won the viscosity
challenge. Molasses has extremely high viscosity.
Consider the Following
Compare the viscosity of liquids and gases when heated. It’s hard to miss a commercial
about motor oil. As the engine heats up, so does _______________. Warm liquid flows
easily. So, we can conclude that heat decreases the viscosity
of oil. That’s why it’s important to change the oil in your car
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often.
What about gases though? With their particles far apart, gases
are already flowing easily. Heating a gas brings the particles
____________________ and they flow less. So, we can conclude that cooling a gas
actually _______________ its viscosity. Heating a gas forces the particles to bump into
each other more often, introducing _________. Friction often acts as a ______________.
So, believe it or not, heating a gas increases its viscosity. Doing the opposite by cooling
a gas must therefore ______________________________.