PRESSURE
Gases are made up of atoms and molecules, which are in constant and rapid motion. The atoms and molecules are constantly hitting the walls and the gas container. In doing so, they exert pressure on the walls.
Gases have no definite shape or volume. The shape and the volume of a gas depend on its container. Compared with solids and liquids, the molecules of a gas are relatively far apart. Hence, they can be compressed, or forced into a smaller space. But if the volume of a gas is decreased, its pressure is increased, because the molecules hit the walls more often and more rapidly. Thus, pressure is in inverse proportion to volume.
A liquid, on the other hand, cannot be compressed. If we try to force a liquid into a smaller space, it seeks a way out of the container. the pressure which a liquid exerts on the walls of a container is equal in all directions. This is why liquids are used for transmitting power in different directions, in hydraulic brakes and elevators.
The more a gas is compressed, the greater its resistance to compression. If a large amount of gas is forced into a small space, it becomes difficult to compress further. Under very high pressure, compressed gas can be used for transmitting power.
As gas pressure is increased, the molecules are forced closer together. If this continues, the molecules eventually become attached to one another. At this point, the gas changes into a liquid.
The pressure of a gas changes with temperature. Pressure is in direct proportion to absolute temperature, since, the higher the temperature, the more rapid the motion of the molecules, and, consequently, the greater the pressure exerted on the walls of the container. Conversely, the higher the pressure of a gas, the higher its temperature. When a gas is compressed, it becomes hotter.
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Say whether these relationships are in direct or inverse proportion. Then, put them in the order in which they occur in the text:
a) compression of a gas: resistance to further compression.
b) change in volume: change in pressure.
c) compression of a gas: increase in temperature.
d) distance between molecules: compressibility of substances.
e) change in temperature: change in pressure.
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AMAZING PHYSICS ( Newton's 3rd Law)
QUESTION: Consider an apple at rest on a table. If we call the gravitational force exerted on the apple "action", what is the "reaction force" according to Newton's third law?
ANSWER: The reaction force is the apple gravitationally pulling on Earth (and NOT the support force by the table). To identify a pair of action-reaction forces in any situation, first identify the pair of interacting objects involved. Something is interacting with something else. In this case, the whole Earth is interacting (gravitationally) with the apple. So, Earth pulls downward on the apple (call it action), while the apple pulls upward on Earth (reaction). Simply put, Earth pulls on the apple (action), the apple pulls on Earth (reaction). Better put, the is a single interaction between the apple and Earth, and they simultaneously pull on each other, with the same amount of force.
- Enseignant: CHAMS_EDDINE KHIARI (Enseignant)