Sunday, September 11, 2022

The Science Behind Grenades Explosions

    For the last couple of weeks, I have been playing the Uncharted series game. It has been quite a challenge to complete all the different difficulties the game has. As you increase the difficulty the accuracy of enemies shot and damage increase to a point where it feels totally unfair, but something that has struck me as unacceptable is how grenades work. Their range of explosion and their damage varies from game to game, and from difficulty to difficulty. I did not know much about grenades so I could not make a proper judgment, therefore I decided to do some research to satisfy my curiosity.

    The grenade I want to describe is an explosive weapon that is thrown by hand which is why it is usually called a “hand grenade”. What I did not know is that there are varieties in the grenade: fragmentation grenade which when explodes it spreads fragments. These are the popular ones, and the ones people refer to when they talk about grenades, shockwaves grenades which propagate a disturbance at high speeds to neutralize. Here you have stun and anti-tank grenades, chemical, and incendiary grenade use chemical reaction to create signals like a smoke bomb and crowd control like tear gas or set fire with temperature as high as 2,200 such as the famous Molotov cocktail.

    They are usually cylindrical in shape and of a size that fits in the hand of an average adult. They also have a time delay to allow the user to stay safe from the explosion.  In cartoons we often see the spherical design of grenades refer to as bombs. Those have a long match that indicates the time of explosion (as the picture below). It is also very popular in pirate movies. 

A cartoon bomb which in disguise is a form of grenade


    The match is used to activate the combustible material inside to set the grenade off. Modern grenades like the M61 (which is not as modern but still very popular) use this idea. This grenade has a safety pin which prevents it from unintentionally exploding. The user holds the striker lever and removes the safety pin which ignites an internal spark that sets off the combustible material to explode. The time delay is about four seconds.
Internal structure of a modern grenade.

    Fragmentation grenades usually can be thrown 130 ft of distance and have a harmful radius of 50 ft, that is about the radius covered by the shrapnel. So, let’s see, an ordinary grenade weighs about 0.9 kg and I want to say one piece of shrapnel weighs 0.005 kg (this is just a guess not an actual measurement). According to Wikipedia a classic hand grenade contains 50g of TNT. Since TNT contains about 4KJ/g this is an energy content of 200 KJ. One shrapnel can easily be traveling at a speed of 9 km/s, which will make it a dangerous projectile to anyone in the radius of explosion. Not only is the explosion that can cause you damage but getting hit by thousands of shrapnel can inflict injuries to anyone, not even being underwater will guarantee your security as you may find in movies, in fact water can be more dangerous as the water can served as a medium of propagation of the shockwave created by the explosion. 

    While playing the Uncharted games I threw a lot of grenades at enemies, and while they remained located less than one feet away from where I threw the grenade, they would continue to move as if nothing happened while when grenades were thrown to me, I suffered damage even while I was in cover. 

    Calculating the effects of a grenade involves a lot of data. You have to take into account how many shrapnel will be created by the blast, take into account the conservation of momentum, the combustible used to consider the energy released by the explosion, the material used to make the outer shell of the grenade. It is not as simple as counting its kinetic energy on release, there are a lot of physics principles that apply in this case. 

 

https://science.howstuffworks.com/grenade2.htm

https://aoav.org.uk/2021/what-is-a-hand-grenade/

https://www.youtube.com/watch?v=VoVNZGwOnZI

https://www.youtube.com/watch?v=W4DnuQOtA8E

https://en.wikipedia.org/wiki/Grenade

https://man.fas.org/dod-101/sys/land/m67.htm

https://physics.stackexchange.com/questions/500552/how-to-calculate-speed-of-shrapnel-based-on-explosives-speed-of-detonation


Tuesday, August 30, 2022

A New Age of Space Exploration

    On July 20th, 1969, hundreds of millions of people all over the world gathered around televisions and radios to listen to the words that mark what today we consider the end of the space race. 

    "Houston, ... The eagle has landed", "That's one small step for a man..." Are phrases that are well known across the world as humanity finally reached to land on the moon. I cannot imagine what that must've felt for the generation who got to live it, but I see its impact on society. Ever since that day, science has received massive support from governments and everyday more and more projects and proposals are created to push forward the boundaries of humankind.   

    The rocket Saturn V was the one responsible for all the six successful missions to the moon and now after years of development the Space Launch System (SLS) will carry the responsibility of the next generation going to the moon. If you are not familiar with it, the SLS is an American super heavy-lift expendable launch vehicle which is being developed in three major phases with increasing capabilities: the first phase denominated Block 1 will be carrying an uncrewed Orion spacecraft on a flight that should last approximately 8 minutes before reaching low-Earth orbit or LEO as it is known. From there on it will prepare for a Trans-lunar injection (TLI) to ensure that Orion will reach the moon and future missions that target deep space exploration. A TLI is a propulsive maneuver used to set a spacecraft on its trajectory to the moon. By increasing the spacecraft velocity, changing its orbit from LEO to a highly eccentric orbit, the spacecraft begins cruising on the lunar transfer arc, its trajectory approximates an elliptical orbit about the Earth with an apogee near to the radius of the Moon's orbit. With the right size and timing of the TLI burn the spacecraft targets the Moon as it revolves around the Earth. This first flight will mark the beginning of the Artemis program.

The Space Launch System block 1 Configuration.


    The Artemis program seeks to reestablish a human presence on the moon since its last time with Apollo 17 in 1972. This time the plan is to create a lunar gateway (sort of a small space station). The long-term vision of the program is to establish a permanent base camp on the Moon that will be used to facilitate human missions to Mars. 

    The first mission officially named Artemis I, will last for three weeks and will test all the rocket stages and spacecraft that would be used in later missions. After performing a TLI it will deploy CubeSat Satellites. These satellites will be used to test long-distance CubeSat communications technology, exploration of ice water on the moon using infrared, and some biological research.  According to plan, Artemis 2 will perform a crewed lunar flyby and will take place in 2024. Artemis 3 will perform a crewed lunar landing in 2025, the Artemis 4 docking with the Lunar Gateway in 2027 and future yearly landings on the Moon thereafter. After so many years of talks and exposition about colonizing Mars and creating a future where interspace flight is possible this mission will officially be the start of a new era. 

 On August 29th, 2022, NASA planned on sending their first rocket with a destination to the moon once more, but a leakage on engine 3 has made a delayed on this, so the next propose date is set for September 2nd.

If you want to learn more about this I suggest the following.

Cycles of Time - A Summary Review Part 2

     If you read the first post on this topic, you’ll recall that the book is divided into three parts. In this publication, we cover some o...