Engineering in Daily Life

1. Short Introduction to Viscosity

Let’s say you have water flowing over a flat plate. For sure, it’s not going to move freely. But why do we say that? The answer to this is: Viscosity. In simpler words, there is a kind of internal friction among the moving layers of the fluid. This resistance doesn’t let the fluid flow freely over the plate.

You can say that: ‘Friction loves keeping all the layers together’. In technical terms, we say: “Friction opposes relative motion”. Having this understanding, consider layer number 2. 

• Layer 3 moves at a faster speed (v+dv) than Layer 2. Hence, the viscous force on the lower layer of 3 acts in such a way that it gets slowed down. 
• Layer 1 moves at a slower speed (v-dv) than Layer 2. Hence, the viscous force on the upper layer of 1 acts in such a way that it gets faster.

This fluid property of trying to keep and move the fluid ‘together’ is known as Viscosity.

The thing that separates the low viscous fluid from the highly viscous fluid is the amount of ‘strictness’ that the fluid shows for keeping them together.

• For example, water is less viscous than honey because water doesn’t care much about keeping the layers moving together. While Honey is like a much ‘strict master’ who wants all of these layers to be united/together

Technical Definition for Viscosity –
The measure of resistance to relative motion within the fluid is called viscosity.

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2. Temperature effect on Viscosity

Temperature does have an effect on the viscosity of the fluid.

• In the case of a liquid, the molecules are bonded by weak chemical bonds. 
• On increasing the temperature, you are actually providing enough thermal energy to the molecules that they break the bonds and become free. This causes the viscosity of fluid to decrease as there is no more dependency of fluid layers on one another because of moving apart. We say the fluid becomes thinner.
• While at much lower temperatures, the fluid tends to become thicker.

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3. Need for Multigrade Engine Oil

We all would agree that an engine is nothing but a machine, and we know that in the case of a machine used in machining operations, there are many parts that require grease for proper functioning.

Similarly, Engine Oil is used to ensure that there is proper lubrication among the contact parts, i.e., with engine oil, we ensure there is no wear and tear among the interacting parts. 

3.1 What happens if oil is too thin or too thick?

• If the oil you use is too thin, it will just flow out of the surfaces very quickly, and hence won’t be of any help

If the oil is too thick, a lot of power would go into just moving the parts through your ‘thick’ oil

3.2 Effect of Temperature on Engine Oil

So, knowing this, we choose a motor oil with a given viscosity. Now, consider 2 cases :

• Case 1: I use this oil on peak summer days
• Case 2: I use this oil in peak winters

We have already discussed the effect of temperature on the viscosity. An oil with given viscosity would become thinner in peak summer and thicker in peak winter.

SOLUTION :
To overcome this, earlier people used a 30-weight motor oil (already thicker) in summers, so that it thins out and reach required value because of high temperature, while they used a 5-weight motor oil (already thin) in winters, so that it thickens to reach the required value in peak winters due to low temperature.

BUT Now, we have come up with something even better, known as ‘Multigrade Engine Oil‘. 

The speciality of this oil is that it can maintain a constant value of viscosity over a wide range of temperatures. Hence, we no longer have to change our oil from season to season. 

• The key feature of multigrade oils is their ability to remain fluid when cold and provide adequate viscosity at higher temperatures.

3.3 How to interpret the rating?

5W-30 means 5 weight in winter and 30 weight in summer. Hence, the viscous nature remains maintained. Now, you know the reason behind 5W-30. Similarly, we also have 10W-40 and many more combinations available in the market

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FAQ section

In this specific article, we are going to learn about the working of GPS. In the upcoming articles, we will be dealing with the interfacing of the GPS module with the Arduino. I feel that it’s important to know the working of the module which we use in our project instead of just learning about ‘how to make the module throw its data values at us”

GPS stands for Global Positioning System and is mainly used to locate the exact location of the receiver with the help of data which it gives (out of which most important is Longitude and Latitude coordinates)

How does GPS locate a position?

The working of the GPS module is based on the communication between the satellites and the GPS receiver module.  For locating the position of a place on earth, we need several parameters like Longitude and Latitude (2-D) and an extra Altitude (for 3-D)

To locate the position, in GPS, we have something known as Trilateration.

In Two-Dimensional Space: 

 we need a total of 2 satellites (say S1 and S2 here). We    are suppose located at point O and we need our location through GPS.

                                                                                  

Text version of the above flowchart

Step-1: The distance between the satellite and the GPS receiver (referred as O) is to be calculated. So we get that O is at a distance of d1 from S1.

Step 2: But still, O can be anywhere on the circle-1 with center S1 and radius as d1.

Step 3: Also, the same thing goes with S2, i.e., O can be anywhere on circle 2 as well.

This implies that, O is somewhere on the region common to circle-1 and circle-2. This means it lies in the points of intersection of circle      1  & 2 (here O and P).

To decide between O and P, we take into account the circle-3 which is the earth surface itself. All the 3 circles intersect at O (therefore, P is eliminated) and hence we obtain the position of a GPS receiver in 2-D.

In Three-Dimensional Space: 

We need a total of 3 satellites for locating position of GPS receiver

Here, we need to consider just the spheres instead of circle. 

For quick overview,

Text version of the above flowchart

Step 1: We get 2 spheres of radius d1 and d2. The intersection gives a circle (say C-1). So ‘O’ must lie on the C-1.

Step 2: Now, we have a third satellite, S3; it measures the distance from O as d3. This implies that O lies somewhere on the sphere (of radius d3).

Step 3: So O lies on C-1 as well as on the sphere of radius d3. This means O must be one of the two points of intersection between the sphere of radius d3 and the circle C-1.

Step 4: For the final answer, we take the fourth sphere – Earth itself. The intersection removes the ambiguity and gives the final point as ‘O’,
which is the actual location of the GPS receiver.

But, there exists a problem of time delay, since the satellites have accurate atomic clocks while the GPS receivers uses the clocks which are installed in mobile phones.

But since all the satellites use the same specifications for atomic clock, the ‘time offset’ is the same. Even error of microseconds can give an error in kilometers !! Hence we use fourth satellite (S4).

As we discussed earlier, that we need the distance ‘d’ for locating the positions of satellites. 

How do We Exactly Determine ‘d’?

The ‘radio signal’ which is sent, it carries 2 information:

• Exact time when it was transmitted (t1)
• Position of satellite

Now the receiver receives the signal at time t2 (say) :

$d = (t1 – t2)\times c$

where c is the speed of light $(3 \times 10^{8}\,\text{m/s})$

What happens inside the GPS receiver

Components involved in GPS (based on the above flowchart):

Antenna: Receives the signal

Filter: It removes the extra signals that are not needed and only keeps the one that has the GPS-related information.

Decoder: Takes out the information from the signal

Output Display: Displays the position on the device

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