Almost Physics IV - Momentum

Post Reply
momo
Golden Member
Golden Member
Posts: 0
Joined: Mon Nov 04, 2013 7:10 pm

My posts are covering basic physics laws, I hope readers are aware that I am still newbie and that what you read in my post is far away to replace the Marshals, Explorers and Rescue team teaching advises through the organized trips. I discourage readers to keep the content of this posts as a standard when driving as the desert may be an hazardous terrain, the beautiful straight dune that you might see on a drawing maybe completely different in real. So please, what you read is just there for general culture.

Before starting, I would like to thank caprihorse for correcting some mistakes in a previous version of this thread, the corrections are mentioned in the post #2 and the video that he commented is here :http://www.youtube.com/watch?v=JWCXZClR0w0
I modified this thread and removed the mistakes to avoid readers to lose time reading incorrect informations. Thanks for your understanding.



Momentum is the product of the mass and velocity of an object.

Momentum= mass . velocity


As the momentum is the product of mass and velocity the international unit is (kg* m/s)


For example, a Hummer H2 (3000 kg mass) on a fast pace, has a large momentum compared to a Suzuki Vitara (1330 Kg) at the same speed.
So if we give an equal break power on both vehicle, it will take more distance to the H2 to stop than the Vitara.


Now if we take two Suzuki Vitara, one is running faster than the other. The faster one would have more momentum. And as result it would take longer time and distance for the faster car to slowdown.


So how momentum is useful on sand track?

As we see the more momentum we have the more distance it takes to stop a vehicle, we use this benefit to avoid us getting stacked on a sand track in some situations. When slowing down or losing the engine power, our vehicle would stay in motion for a short time, we can therefore accelerate again without need to stop.

Momentum is useful when crossing the dune crest. If you reach the top of the dune and your vehicle is almost horizontal, the momentum will help you to pass the crest depending on your arrival speed, in other word to bring the crest edge closer to your rear tires without the need of your engine power.


Momentum in other words means that your car velocity is non-null. So we use it often at each drive as synonym meaning keep moving and don’t stop.


I hope this gives you a better overview about momentum. I will be discussing in the next chapter briefly “Pressure” before moving to the key point in desert drive which is Energy and Law of conservation of energy.

Any clarification or correction are most welcome.


Thank you for reading this thread,

Regards,

Momo
User avatar
caprihorse
Golden Member
Golden Member
Posts: 9
Joined: Tue Nov 16, 2010 1:23 am
Location: Bratislava, Slovakia
Contact:

Now really I cannot resist anymore to respond to what I'm reading...
MOMO;35604 wrote:This kind of areas in the desert where your vehicle doesn't stack if you have good amount of momentum, is the area where probably people have driven before you. So the softness of the sand is not equal as you go on, some parts are compacted some are not. It means you will have spaced little areas where your tires have good grip and performance and others where your tires sink into the sand.
Wrong ! The best for driving is fresh sand, not broken, as it has higher surface pressure and the tyres have higher grip, compared with the sand which was already driven. Additionally crossing the tracks is causing the suspension and tyres to bounce, so the car is loosing the grip.
MOMO;35604 wrote:The momentum here will help you to virtually jump between two compacted areas. Compacted area are very random, it might be there every 50cm – 60cm or even 1m left and right…anywhere. It comes as a natural phenomenon when cars pass over and are bouncing. When it bounce downward it compact the area and so on creating macro-dunes.
Wrong ! Higher momentum (acceleration), will cause you at climbing, rear wheels to do more digging. The best is to keep your car driving with a stable appropriate speed in such a situation, to try not to jump.
MOMO;35604 wrote:Here is a video where I got stacked in soft sand area, you can watch how the sand look like in such areas and see how speed affect the situation. Here two more factors where increasing the problem: my tires not properly deflated, we will explain than in the next chapter. And I was facing a small amount of F1* aswell.


The result of your car getting stuck is not because of the inappropriate momentum, but because of wrong trajectory. If you would drive one meter to the left (higher), you would pass with the same momentum. As you were blindly following the bumper in front of you, even 10x higher momentum would not help you.
[0:23] - You should recognize how Pajero in front of you is sliding and fighting the gravity.
[0:24] - You should decide to take the different track, not to decrease your F2.
[0:30] - Same as with Pajero, happened to you. Your rear part is pulled down, as Fg (constant force) and reduced F3 and F2 is resulting in increased F1.
[0:32] - It's clearly seen that you are trying to fight Fg (mission impossible), steering left up, instead of using Fg to your favoure and make additional round to the right, to increase F2.
[0:42] - Your car refused to move, as you were crossing many track and your suspension was bouncing heavily, you lost the traction and grip.
[0:51] - You tried again to beat the result of forces F1 (little Nm) and Fg (huge Nm), where F2 was zero. So you were trying to neglect Mr. Newton's basic law, which caused you to return.
[1:04] - ... but not enough, as at this moment you sill do not trust Mr. Isaac, as you could not recognize, that in your new place nothing did change in the layout of forces F1, F2, F3 and Fg.
[1:19] - The forces layout is changed with the terrain profile. Naturally you zeroed F1, F3 and Fg are stable, so with momentum you could produce pulling force F2.

So as the result in off-roading the right judgment is the basic law. On the other hand the right judgment can be learned as the fact only by many wrong decisions. How long it takes, depends on the individual. Some Newbies in our Club are staying and will remain to be Newbies forever, because of wrong judgement.

Here is again the picture explaining forces from your previous articles.

Image
momo
Golden Member
Golden Member
Posts: 0
Joined: Mon Nov 04, 2013 7:10 pm

Thank you caprihorse for reading my thread and correcting me. I know I am new nightmare for you but please don't resist to respond my threads, I like your point of view and you are making these threads rich in informations. Thanks again.
User avatar
Defragmantor
Intermediate
Intermediate
Posts: 0
Joined: Tue Jun 25, 2013 5:12 pm

U never stop learning while offroading :D the technique to take a new track rather than a chewed up one is a very good tactic if your trying to climb steep dunes . I hate hatta for the same reason too many chewed up tracks so no fresh sand to climb :p
momo
Golden Member
Golden Member
Posts: 0
Joined: Mon Nov 04, 2013 7:10 pm

Actually when mentioned the soft sand area with plenty of tracks, I don't recommend it as best place to drive. Of course fresh sand is heaven for an off-roader, I am just saying that momentum HELPS to cross it. I had a driving lesson previously, on such terrain almost horizontal, the only way to go is to floor it at high RPM.
User avatar
Abu Jimmy
Marshal
Marshal
Posts: 121
Joined: Sat Feb 26, 2011 5:54 pm
Location: Sharjah
Been thanked: 1 time

Defragmantor;35612 wrote:. I hate hatta for the same reason too many chewed up tracks so no fresh sand to climb :p
Every rule has an exception , In certain areas you will find out that the best rout is to follow exactly the tyre prints of the cars in front which will compress the powdery soft sand ahead and it will make it easier to climb ( such as LIWA sand dunes )...:whut:
What goes around , comes around .
Post Reply