Category: Physics

The Compressibility Factor

The Compressibility Factor

The Compressibility Factor

09/23/17

“How can we quantify how much a gas deviates from its ideal form?”

 

In introductory chemistry and physics classes, all gases are assumed to be completely ideal. However, in the real world gases usually are not so easy to work with. So how can we quantify a gas’ deviation from its ideal form? Well, let’s start from the basics. We know that all of the gas’s properties can be completely related to one another through the ideal gas equation p*v_specific=r*T. It would logically follow that if we were to divide the product of the pressure and the product of the specific volume by the universal gas constant times the temperature, we should end up with a ratio of 1/1.So what if we were to find out a gas’s specific volume, temperature, and volume of a gas in its non-ideal form, take their ration, and use that as a constant in a modified ideal gas equation? This is known as the compressibility factor and is commonly represented as z in the non-ideal gas equation p*v_specific=z*r*t.

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Pulse-width Modulation

Pulse-width Modulation

Pulse-width Modulation

09/18/17

“How can we use a digital signal to control power appliances?”

Using sinusoidal analog signals for control applications has drawbacks. Specifically, the constantly changing signal can cause the resistors on a circuit to heat up and induce damage. However, how can we use our engineering mindset to fix this problem? Well, what if we were to replace this analog system with a discrete one operating at a duty cycle? That way we can imitate the perpetually switching signal while avoiding the issues that come along with it. This type of signaling is known as pulse-width modulation and is one of the fundamental ideas of modern control theory

 

The Strange Second State of Water

The Strange Second State of Water

 

The Strange Second State of Water

09/17/17

“Can water have a second liquid state?”

 

Water is a most peculiar molecular compound. Although this material composes over sixty percent of the human body and the vast majority of the Earth’s surface area, we still know very little about the chemical and physical properties and behaviors of this element. And this idea could not be better exemplified by a most recent discovery lead by a highly intelligent group of scientists.

At Oxford University, A group of physicists led by the postdoctoral research assistant Laura Martinez Maestro had decided to conduct a new experiment on water (Crew, Bec). For this, they took a sample of water at zero degrees Celsius and increased the temperature slowly until it reached one hundred degrees Celsius while measuring the thermal conductivity, refractive index, conductivity, surface tension, and the dielectric constant. Once the water hit, 40 degrees Celsius, its properties started to shift drastically, and once it had hit 60 degrees Celsius all of its properties had changed into something new. Specifically, the temperature of change was 64 degrees Celsius for thermal conductivity, 50 degrees Celsius for refractive index, about 53 degrees Celsius for conductivity, and 57 degrees Celsius for surface tension.

Why does this happen? Although everything seems murky at the moment, this phenomenon might be a consequence of the fact that water molecules only have a very weak bond with one another, and that the bond between oxygen and hydrogen is far greater than the hydrogen-hydrogen bonding. As a result, the molecular structure of  molecules is constantly changing and reforming, leading many to believe that this might be the cause for the strange second stage of matter

 

References

Crew, Bec. “Physicists Just Discovered a Second State of Liquid Water.” ScienceAlert, ScienceAlert, 14 Nov. 2016, http://www.sciencealert.com/physicists-just-discovered-a-second-state-of-liquid-water.

On water’s expansion with freezing

On water’s expansion with freezing

On water’s expansion with freezing

09/16/17

“Why does water expand upon freezing?”

The variation of volume with thermal energy for most liquids has a very simple characteristic. When heat is applied, the volume increases, and vice versa for cooling. This is because the added (or subtracted) energy will cause the amplitude of the vibrations of the molecules to change, thereby modifying the volume. For example, when a liquid freezes, the molecules will pack into one another, thereby shrinking the volume.

However, water exhibits a very peculiar phenomenon. When water is cooled to its freezing point, its volume will actually expand. Why does this happen? Well, let’s analyze it using our scientific mindset. Unlike most other molecules, water has a very unusual structure. Specifically, a water molecule’s primary form of bonding is based on hydrogen bonding. When temperature decreases, the strength of a hydrogen bond actually increases (since the lower thermal energy means that the hydrogen bonds will have less vibrational energy, therefore lowering the chance to shake out of position and increasing stability).

Once water is cooled into ice, the only bonding will be hydrogen bonding. Specifically, it will be bonded in a hexagonal structure, which is a much more “open” network than most structures. The tandem of hydrogen bonding and a hexagonal structure vastly decreasing the density (Levine, Scott 2013). And because density is described by the equation, with being the density,  being the mass, and being the volume, and as mass is constant, when the density decreases the volume must increase as a result. Consequentially, the volume of water increases upon freezing! This fact has multiple implications. For example, a lower density of ice means that ice will float in water, which allows for complex structures such as ice glaciers to occur naturally.

 

References

“Why Does Water Expand When It Freezes? .” FAQ: Water Expansion on Freezing, New York University, 3 Dec. 2013, http://www.iapws.org/faq1/freeze.html.

Liquid pressure variation with height

Liquid pressure variation with height

Liquid pressure variation with height

09/12/17

“How does the pressure of a liquid vary with height?”

 

Liquids are famous for their permeable structure, such that you can insert an object at any point inside it. However, depending on which part of the height you insert it, it will experience a different pressure. So how can we quantify this pressure variation with height? Well, if we investigate empirically, we will find out that this variation can be symbolically represented as P = rho*g*h, with P being the pressure, rho being the density, g being the gravitational acceleration, and h being the height.

Diffuser (thermodynamics)

Diffuser (thermodynamics)

Diffuser (thermodynamics)

09/08/17

“How can we slow down a fluid while increasing its pressure?”

 

When working with fluids, we often want to modify its properties in some meaningful way. This could include changing more than one at once, such as slowing down its velocity while increasing its pressure. So how exactly can we accomplish this? Well, what if we were to just get a machine to do this? This is the exact idea behind a diffuser, which is the basis of operation for multiple types of HVAC systems.

Deadband

Deadband

Deadband

09/05/17

“Do some control systems have a zone with no feedback?”
Ideal controls systems are available to take in all possible frequencies. Some controls systems have a zone where the input frequency will return nothing. This region is known as the deadband and can be used to prevent unwanted side-effects.