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SS1: PHYSICS – 3RD TERM

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  1. Production of Electric Current | Week 1
    6 Topics
    |
    1 Quiz
  2. Electric Current | Week 2
    5 Topics
    |
    1 Quiz
  3. Electrical Resistance of a Conductor | Week 3
    5 Topics
    |
    1 Quiz
  4. Particulate Nature of Matter | Week 4
    5 Topics
    |
    1 Quiz
  5. Crystalline and Non-crystalline Substances | Week 5
    3 Topics
    |
    1 Quiz
  6. Elastic Properties of Solids | Week 6 & 7
    4 Topics
    |
    1 Quiz
  7. Fluids at Rest & in Motion | Week 8 & 9
    6 Topics
    |
    1 Quiz
  8. Solar Collector
    3 Topics
    |
    1 Quiz



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Cohesion is the force of attraction that exists between molecules of the same substance e.g the force of attraction between molecules of water (water and water).

Adhesion is the force of attraction between molecules of different substances. e.g the force attraction between water and a glass surface.

Cohesion and adhesion, as defined above, explain the different actions of water and mercury when spilt on a clean glass surface.

The Reason Water Wets Glass:

The force of attraction between molecules of different substances (adhesion), like water and glass surface, is stronger than the cohesive force existing between molecules of water, hence, water spreads out on the surface of the glass and wets the glass.

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Water spreads when spilt on clean glass.

Reason Why Mercury Does Not Wet Glass:

When mercury is spilt on a glass surface, the mercury does not spread or wet the glass, instead, it forms goblets or spherical beads (balls). This is due to the fact that the cohesion force of mercury molecules is stronger than the adhesion force between mercury molecules and glass molecules.

mercury on glass surface
Mercury forms goblets on glass surface.

This also explains why the mercury level in the tube will fall as discussed in the previous topic.

So we can see why mercury does not wet glass whereas water wets glass.

These adhesion and cohesion forces are responsible for the rising and fall of liquid in a capillary tube. The adhesive force pulls water up the side of the tube. Causing water to creep up inside the tube.

Capillarity action causes;

1. Water to rise in the stem of a plant.
2. Blotting paper to absorb ink.
3. Blood to spread through fine capillary tunnels in the body.

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