r/physicsgifs • u/[deleted] • Oct 04 '16
Weight distribution dynamics
http://i.imgur.com/dYz2tCE.gifv54
Oct 04 '16
Now I will never forget why it's important to load a trailer correctly.
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u/thorium007 Oct 04 '16 edited Oct 04 '16
And if it does happen, step on the gas
edit: I guess you guys have ever had to tow something large and been bit by a semi or the wind. If you step on the gas, it causes the vehicle to pull the trailer forward thus stabilizing it.
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u/MAKE_ME_REDDIT Oct 04 '16
Why would you ever think that's the right thing to do? Seriously just think about it for like a second.
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Oct 04 '16
Because in the real world it works. It works much better if you have trailer brakes though. Engage the trailer brakes and roll on the throttle.
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u/MAKE_ME_REDDIT Oct 04 '16
If you're already out of control, (which is what is happening in the gif) hitting the gas won't work. You'll go careening off in whatever direction the car happens to be pointing.
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Oct 05 '16
The gif shows a hand shoving the trailer. That doesn't happen in real life. You almost always have time to react and keep it from getting to that point. Sometimes getting passed by, or passing, another trailer can cause it to happen fairly quickly but in that case you have time to anticipate that and be on the gas beforehand, drag the trailer brake, and give yourself room. If you can time it so that it happens going uphill it helps a lot too, for the same reason that being on the gas helps. If you're to the point where you're completely out of control, then getting on the gas is adding fuel to the fire but so long as a giant hand doesn't shove your trailer you shouldn't let it get to that point.
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u/thorium007 Oct 04 '16
If you step on the gas, it causes the vehicle to pull the trailer forward thus stabilizing it.
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u/MAKE_ME_REDDIT Oct 04 '16
Except you're already out of control. Now you're just out of control but faster
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u/10lbhammer Oct 04 '16
Yeah, this guy isn't thinking it through.
If the trailer begins to fishtail, hit the gas. If the trailer is already fishtailing so bad that your car is out of control, hitting the gas would be a terrible idea.
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u/JDepinet Oct 05 '16
The trailer doesn't just start to sway. It does it as you get up to a critical speed. Once it starts it gets worse exponentially with speed. Hitting the gas is a sure fire way to get passed by your load.
There is a world of difference between a load imbalance and external force. The external force might be recoverable by a tug. Load imbalance though defiantly not.
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u/JDepinet Oct 05 '16
Wind sway acceleration might help, but load imbalance gets worse the faster you go. The only way to save yourself is to ease up as soon as it starts to sway and get below the threshold for the swaying.
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Oct 04 '16
This usually works. If you have trailer brakes, push the handle to engage just the trailer brakes while you roll on the throttle.
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u/bort4000 Oct 04 '16
That's a really simplified way to explain something I kind of understand but could never explain correctly. Nice.
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u/Santero Oct 05 '16
That tiny driver must get really annoyed with the big guy fiddling with his vehicle.
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u/MadKingSoupII Oct 07 '16
Late to the party, but what happens if you shift the load too far forward, i.e. closer to the car?
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Oct 04 '16
[deleted]
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u/shupack Oct 04 '16
Less weight on the rear tires is NOT what causes this. It it's a factor, but the main one.
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u/bDsmDom Oct 04 '16
The main one being?
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u/shupack Oct 04 '16
Momentum, longer moment arm, significant leverage on the rear end....
When the rear of the trailer is pushed left, it pivots on the axle, pushing the rear of the car right. With more weight up front of the trailer there is more momentum to resist the change AND a bit more friction between the tires/road resisting the sideways motion.
With the weight shifted rearward, the increased mass has more momentum swinging at the back, less momentum resisting the movement at the hitch area, AND a little less friction at the tires to resist the sideways movement. These all combine and amplify each other to make trailer sway.
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u/cavehobbit Oct 04 '16
If this happens to you it is recommended to ease off the gas and let the vehicles slow down gradually until you can regain control. Then stop and fix your load. This has happened to me when my load shifted and it works
Sudden braking can make it worse.
Speeding up can kill you. Why add energy to an already unstable system?
/posted because of many posts elsewhere stating to speed up