Physics

Article about Pressure in fluids

In physics, the pressure is defined as force per unit area, where the direction of the force is perpendicular to the surface area. Mathematically, pressure is expressed by the equation P = F / A, where P = pressure, F = force and A = surface area. Force unit (F) is Newton (N), the unit of area is the square meter (m²). Because pressure is the force per unit area, the pressure unit is N/m². Another name for N/m² is Pascal (Pa). Pascal was used as a pressure unit to honor Blaise Pascal.

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Article about Density and specific gravity

Density

One important characteristic of a substance is density. Density is the ratio of mass to volume. Mathematically written:

ρ = m / V

ρ (rho) is a Greek letter commonly used to express density, m is mass and V is volume. The density of the homogeneous fluid is different from the density of a homogeneous solid. Iron, for example, have the same density in each part. In the Earth’s atmosphere, the higher the atmosphere from the surface of Earth, the smaller its density, while for seawater, the deeper the seawater, the greater its density. The density of a homogeneous fluid can depend on environmental factors such as temperature and pressure.

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Article about The applications of Bernoullis principle and Bernoullis equation

Torricelli’s theorem

One of the uses of Bernoulli’s equation is to calculate the speed of a liquid exit from the bottom of a container (see figure).

We apply Bernoulli’s equation at point 1 (surface of the container) and point 2 (surface of the hole). Because the diameter of the hole in the bottom of the container is much smaller than the diameter of the container, the speed of the liquid on the surface of the container is considered zero (v₁ = 0). The surface of the container and the surface of the hole are open so that the pressure is equal to atmospheric pressure (P₁ = P₂). Thus, Bernoulli’s equation for this case is:

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Article about Bernoullis principle and Bernoullis equation

When we ride a motorcycle, the clothes we use are swollen backward. Sometimes, if the wind blows hard, the door can close itself. Though the wind blows outside the house, while the door is inside the house.

This can be explained using the Bernoulli’s principle. Daniel Bernoulli (1700-1782) discovered a principle that could be used to explain the above phenomenon.

Bernoulli’s principle

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Article about Equation of continuity

Try to open the water tap slowly while paying attention to the speed of the water coming out of the mouth of the faucet. Now compare, where is the rate of water flow faster, when the mouth of the faucet is closed or not? Why is that? To understand this, please learn the continuity equation.

Streamline

In a steady stream, the speed of each fluid particle at a point, say point A is always the same. When passing point B, the velocity of the fluid particles may change. However, when arriving at point B, the fluid particles that follow from behind flow at the same speed as the fluid particles that precede it. Likewise when coming at point C and so on. The Flow Line is a curve that connects points A, B, and C.

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1. Definition of Black principle

If we mix hot and cold water in an open container (for example a bucket), heat transfer from hot water to cold water. Because the container is open, then some heat moves into the air. The container also becomes warmer. Heat released by hot water is not only absorbed by cold water, but also absorbed by atmosphere and containers. In this case, the bucket is a non-isolated system. When we mix hot and cold water in a closed thermos, heat transfer from hot water to cold water. Thermos are isolated systems, so no heat moves into the air or a thermos. Cold water only absorbs the heat released by hot water until the mixture of hot water and cold water reaches the thermal equilibrium.

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1. Definition of the heat transfer by radiation

How does it feel if you wear black clothes on a hot day, or when are you exercising during the day? Compare with when you wear white clothes? If you wear black clothes during the day, then you feel hot. Why is that? The distance between the sun and the earth in the morning is almost the same as the distance between the sun and the earth during the day and evening. Then why are the mornings and evenings cooler, hotter during the day? The answers to these questions are related to heat transfer by radiation.

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Article about The heat transfer by convection

Ever been by the beach when it was sunny? On a clear day, on the beach, there is always wind blowing from the sea. Why is there always a wind on the beach, and why do the sea breeze (winds blowing from the sea to the land) occur during the day, the land breeze (winds blowing from land to sea) occur at night? Why in the rainy season can cloud come down to the slopes? Why does the wind feel cool? The answers to these questions relate to the specific heat of land and sea, expansion, density, and heat transfer by convection!

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1. Definition of the heat transfer by conduction

If you sit in a wooden chair, the surface of the wooden chair becomes warm. Conversely, if you sit in a chair made of plastic or metal, the surface of a metal or plastic chair does not feel warm after sitting. Why is the surface of the wooden chair heated, while the metal chair surface is not? Why can sleep on a cold floor without a mattress cause pain? Have you ever worn an anti-cold jacket? Why are most anti-cold jackets made of wool? There are still many things that can be considered and questioned related to the subject of heat transfer by conduction.

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Article about Latent heat specific heat and heat capacity

If you put a mercury thermometer into a container containing a mixture of cold water and ice, you will observe after moving downwards, the surface of the mercury stops moving. Mercury’s surface stops moving after reaching the temperature of the freezing point of the water (0 ^oC). If the container is open, heat flows from the air that has the high temperature to the mixture of ice and cold water. The addition of heat from the air causes the ice to melt. As long as ice melts, does the temperature of the mixture of the ice and cold water change? As long as ice melts, the temperature of the mixture of water and ice does not change.

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