The Physics of a Hanukkah Dreidel
“How does a Hanukkah dreidel spin?”
Hanukkah dreidels are great fun for people of all ages. These little tops are able to spin round and round with a very peculiar pattern. However, why exactly do they spin? Well, let’s use our scientific mindset to find out. All spinning objects with mass have a property called angular momentum. The more moment of inertia it has and the greater spin then the greater angular momentum it will have. Angular momentum tries to be conserved so a dreidel will try to keep on spinning when acting upon!
Happy Hanukkah, and Happy Holidays to everybody!!!
Entropy Changes of an Ideal Gas
“How does the entropy of an ideal gas change with time?”
When an ideal gas undergoes a nonadiabatic process, it’s entropy is bound to change. However, how can we quantify such a change? Well, let’s use our engineering mindset to figure this out. One way would be to look at a thermodynamic property table, find the specific enthalpies for different temperatures, and then take the difference in values. Another way would be to plug in the equation delta s = C_v*ln(t2/t1) + R*ln(v2/v1) or delta s = C_p*ln(t2/t1) – R*ln(p2/p1).
“How do metals waste away with time?”
Metals are some of the most widely used materials in the world. However, nothing within the realm of physics lasts forever. If a metal is immersed in an atmosphere, then it will be surrounded by chemicals alien to its own. Chemical reactions are bound to occur, and over time this metal will decay and waste away in a process known as corrosion. Corrosion is a very important engineering factor, especially for public infrastructure. So much so that in 1998 alone the total annual direct cost of corrosion in the U.S. was around. $276 billion!
The Dew Point
“How can we measure the point in which saturation occurs?”
When it gets humid outside, it’s very easy for moisture to appear on surfaces. However, why does that happen? Well, the answer lies in a most interesting property called the Dew Point. The dew point is the temperature at which the gas in a given area will condense into a liquid. If an object cooler than this point comes in contact with air, then it is possible for dew to form. HVAC system engineers must keep this value in mind when designing dehumidifier equipment.
The Heat Index
“How can we measure how a temperature really feels?”
We all know how to read a normal thermometer. However, when it gets really humid, then oftentimes it will feel much hotter than it really is. So how can we use our scientific mindset to quantify this phenomenon? Well, what if we were to create a formula that combines both the absolute temperature and the relative humidity to produce a value? Well, this is the idea behind the heat index and is used by weather forecasters and HVAC systems analysts all over the world.
The Compressibility Factor
“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.
“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