Water beads up on an oily sunbather, but not on her neighbour, whose skin is not oiled. Explain in terms of cohesive and adhesive forces.
Water do not bead up as the skin is not oily, the adhesive force is more between skin and water molecule.
Fluid statics, often known as hydrostatics, is a branch of fluid mechanics that investigates the state of balance of floating and submerged body, as well as the pressure in a fluid, or imposed by a fluid, on an immersed body.
Cohesive forces are attractive forces between molecules of the same sort. Because cohesive forces hold the molecules together, liquids may be held in open containers. Adhesive forces are the attractive forces that exist between molecules of various sorts.
Liquid drips, for example, adhere to glass panes as a result of such pressures.
We will look at the effects of cohesive and adhesive forces in liquids in this section.
Water molecules bind to one another due to cohesive force. Because oil repels water molecules, it is impossible for water to reach the skin's surface.Because the adhesive force between oil and water is so low, water molecules stay together to form beads owing to the high cohesive force.
The adhesive force between water molecules is almost equal on dry skin, therefore water spreads out on the skin and does not bead up.
Hence, the skin is not greasy, water does not bead up, and the adhesive force between the skin and the water molecule is greater, therefore water spreads.
When a person sits erect, increasing the vertical position of their brain by 36.0 cm, the heart must continue to pump blood to the brain at the same rate. (a) What is the gain in gravitational potential energy for 100 mL of blood raised 36.0 cm? (b) What is the drop in pressure, neglecting any losses due to friction? (c) Discuss how the gain in gravitational potential energy and the decrease in pressure are related.
Consider a group of people trying to stay afloat after their boat strikes a log in a lake. Construct a problem in which you calculate the number of people that can cling to the log and keep their heads out of the water. Among the variables to be considered are the size and density of the log, and what is needed to keep a person’s head and arms above water without swimming or treading water.
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