In the previous chapters, we looked at the behavior of solids.
In the next three chapters, we will discuss the behavior of liquids and gases, which play an important role in the life sciences.
The forces that bind the molecule explain the differences in the physical properties of liquids and gases.
Solids have a definite shape and volume because they are rigidly bound.
The binding of the molecule is strong enough to maintain a definite volume, but not strong enough to maintain a definite shape.
A liquid's shape can be changed by the vessel in which it is contained.
The molecule are not bound to each other in a gas.
A gas does not have a shape or volume, it fills the vessel in which it is contained.
Solids and fluids are governed by the same laws of mechanics, but fluids exhibit some phenomena that are not found in solid matter.
In this chapter, we will show the properties of fluid pressure, buoyant force in liquids, and surface tension with examples from biology and zoology.
When a force is applied to one section of a solid, the force is transmitted to the other parts of the solid with the same direction.
A fluid's ability to flow makes it transmit a force uniformly in all directions.
The force of a fluid at rest is relative to the area.
A fluid in a container exerts force on all parts of the container.
Any object immersed in a fluid exerts force on it.
The weight of the fluid above increases the pressure in the fluid.
A column of mercury is 1mm high and exerts one torr.
All other points in the liquid are unaffected by the increase in the pressure at any point.
The mechanical advantage of a lever is similar to 1.
The muscles pull on the bones of the skeleton.
The sea anemone and the earthworm lack a firm skeleton.
Many of the animals use Pascal's principle to move their bodies.
For the purpose of understanding the movements of an animal such as a worm, we can think of the animal as consisting of a closed elastic cylinder filled with a liquid; the cylinder is its hydrostatic skeleton.
The worm is thinner and longer because of the contraction of the circular muscles.
Contraction of the longitudinal muscles causes the animal to be shorter and fat.
The animal bends toward the contracting side if the longitudinal muscles only contract on one side.
By anchoring alternate ends of its body to a surface, the animal can move forward or backward.
The direction of motion is changed by longitudinal contraction on one side.
The forces inside a moving worm can be calculated.
The force causes a pressure inside the worm.
As follows, the force is calculated.
Pressure inside a worm is calculated.
The pressure is relatively high.
It can raise a column of water.
The longitudinal muscles action can be analyzed.
A body partially submerged in a fluid is supported upward by a force that is equal in magnitude to the weight of the fluid.
The principle is found in basic physics texts.
The power required to remain afloat in water will be calculated using the principle of Archimedes.
The animal must perform work in order to not sink if its density is greater than water.
The problem is similar to the hovering flight that we discussed in Chapter 6.
The limbs can be pushed against the water.
The upward reaction force that supports the animal is caused by this motion.
This is the rate of change in the water.
The moving limbs apply the change in the momentum to the water.
The work done by the treading limbs goes into the water.
The mass accelerated each second causes the water to have half the energy of the water.
We neglected the energy of the limbs in our calculation.
It is assumed that the density of the animal is greater than the water.
The bones and swim bladders of some fish allow them to float in water without consuming energy.