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Old 01-24-2023, 12:28 PM   #1 (permalink)
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Will moving the mass of a vehicle forward while it is travelling, cause it to coast farther ?

I did look this up online, but am not seeing this specific question.
I was seeing that 'Redneck' entered his dually pickup in the Green Grand Prix.
No aeromods at all. LOL
It got me to wondering though what would happen if he had a weight in the back that he would slide forward as he began a coast.
Besides causing the front tires to blow out and the rear to lose grip and spin out, what would happen to the truck ?
I'm guessing nothing at all.
The vehicle would not coast farther, since the object being moved forward in the bed of the truck is part of the truck itself.
What law of motion is this ?
I have a learning disability, so please pardon the childish questions.
This does make me think of an amusing incident in my family.
A relative of mine tricked out his van ( late 1970's ) when they were a thing.
Brand new mag wheels and tires, shag carpet, and to top it all off, a waterbed.
He was feeling good and cruising along at a good speed.
Suddenly, he had to slam on his brakes for a red light.

The van came to a screaching halt, blowing out the front tires, and releasing over 100 gallons of water as he opened his door.

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Old 01-24-2023, 01:01 PM   #2 (permalink)
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I'm not sure of the effect but I'm suspicious of the proportions. Gross vehicle weight vs the moving part.

Short coast vs long coast?
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Old 01-24-2023, 01:24 PM   #3 (permalink)
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Quote:
Originally Posted by Cd View Post
what would happen to the truck ?
I'm guessing nothing at all.
The vehicle would not coast farther, since the object being moved forward in the bed of the truck is part of the truck itself.
What law of motion is this ?
Correct. Every action has an equal and opposite reaction (Newton's 3rd law of motion). When the weight is pushed forward, it proportionally pushes the rest of the truck back.

The only way to push the weight forward without equally robbing momentum from the truck is to push it externally, or for it to have it's own propulsion like a rocket.

By the way, the momentum is conserved because it's all part of the truck. The speed of the truck will change as the weight moves, but return to original speed once it comes to rest.
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Old 01-24-2023, 02:07 PM   #4 (permalink)
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Thanks.
What explains the continued momentum of objects inside the truck as brakes are applied ? ( the example of my relative with the van )
The objects within the vehicle are slowed by the application of the brakes, since they are contained in the body being slowed.
But yet they continue to fly forward..

The only way that I could think that a moving weight might help is when coasting on a decline.
I'm guessing the movement of mass from gravity might give a slight boost in coasting ? ?
Think of a semi with a trailer full of loose cargo.
If it suddely coasted downhill, and the load slid to the front of the truck, would it do anything due to ( gravity ? )

I know this is all 3rd grade science here. Sorry.
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Old 01-24-2023, 02:34 PM   #5 (permalink)
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Quote:
Originally Posted by Cd View Post
What explains the continued momentum of objects inside the truck as brakes are applied ? ( the example of my relative with the van )
The objects within the vehicle are slowed by the application of the brakes, since they are contained in the body being slowed.
But yet they continue to fly forward..
That's Newton's 2nd law of motion, that an object in motion stays in motion unless acted upon by a force. All of the individual parts of the truck that are securely attached can't move, so when the tires start slowing the truck as the brakes are applied (the tires push forward on the road surface), all of the firmly attached parts push on the the part they are attached to.

As the vehicle slows, the rear bumper pushes on the brackets that support it, which pushes on the frame, which pushes on all the other material of the truck. All of the objects want to continue on their original trajectory, but now that the tires are pushing forward on the road, the vehicle pushes backwards in proportion.

Quote:
I'm guessing the movement of mass from gravity might give a slight boost in coasting ? ?
Think of a semi with a trailer full of loose cargo.
If it suddely coasted downhill, and the load slid to the front of the truck, would it do anything due to ( gravity ? )
This is harder for me to conceptualize and explain.

If the cargo started out in the front of the truck as it started up the hill, it would all slide back and slightly slow the truck as it hit the back wall. Essentially the truck didn't "know" there was mass in it until it collided with the wall and started increasing the objects potential energy by hauling it up the hill.

When the truck heads downhill, the weight slides forward, hitting the forward wall of the truck and transfers that potential energy into a tiny bit of speed absorbed by the truck.

The net result of the slowing down and speeding up is exactly the same. There simply is no passive way to gain energy, as that would be a perpetual motion machine.

Changing the velocity of an object (either the speed or direction of travel, or both) requires an expenditure of energy.

If that's not confusing enough, the really interesting thing is that if a truck hits a brick wall, the rear of the vehicle doesn't "know" that until the speed of sound in the materials of the truck reach it.

Here's an example of a slinky being dropped. The bottom of the slinky doesn't "know" it's been dropped until all of the molecules above it have begun to move.


I used to think maybe we could communicate faster than light using physical objects. Imagine a steel rod extending from Earth to the moon. I tell the person on the moon that I will signal them by pushing on my end of the rod, and they see it move on their end. Turns out the speed of sound in steel is 5,100 m/s. It would take almost 21 hours from the time I pushed until they saw their end move. Light on the other hand only takes 1.25 seconds.
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Old 01-24-2023, 03:09 PM   #6 (permalink)
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Thanks for the answers guys !
I found that last bit about the steel rod to the Moon example to be absolutely fascinating !
Absolutely. Fascinating.
I had no idea things worked like that.
Freebeard, not ignoring you. I am however too dense to know if you are sincere, or just poking fun at the question.

I've been fascinated by numbers since forever.
However, my mind can't understand basic math.
It gets lost half way into a math problem and I have to start over.

I would always go to the "Specifications" section of something because I found the numbers fascinating.

I started looking at cD values as a teen.
Some of the same magazine articles Aerohead has posted are ones I collected as a kid.
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Old 01-24-2023, 03:35 PM   #7 (permalink)
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Quote:
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I found that last bit about the steel rod to the Moon example to be absolutely fascinating !
As a tangent to that tangent, that's the basic theory behind the relativity of time, and time travel.

In the steel rod example, the "information" about being pushed on one end could only travel as fast as the speed of sound in that material as molecules push into their neighboring molecules, which then push into their neighbors.

If the sun just instantly vanished, we would continue enjoying sunshine for 8 more minutes, and would have no way to know it had disappeared until the last of the light traveled the 8 minutes to us. Even stranger, the earth would continue to orbit around where the sun was for those 8 minutes, because even gravity propagation can't exceed the speed of light.

If you could hitch a ride on a photon of light, your journey would begin and end exactly at the same moment. From the perspective of the first photons emitted at the beginning of the universe billions of years ago, zero time has elapsed.
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Old 01-24-2023, 04:13 PM   #8 (permalink)
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Quote:
Freebeard, not ignoring you. I am however too dense to know if you are sincere, or just poking fun at the question.
I know, right?

My suspicion is that it would bend the curve of the vehicles deceleration, but not move the end points.
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Old 02-03-2023, 02:48 PM   #9 (permalink)
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what explains

Quote:
Originally Posted by Cd View Post
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What explains the continued momentum of objects inside the truck as brakes are applied ? ( the example of my relative with the van )
The objects within the vehicle are slowed by the application of the brakes, since they are contained in the body being slowed.
But yet they continue to fly forward..

The only way that I could think that a moving weight might help is when coasting on a decline.
I'm guessing the movement of mass from gravity might give a slight boost in coasting ? ?
Think of a semi with a trailer full of loose cargo.
If it suddely coasted downhill, and the load slid to the front of the truck, would it do anything due to ( gravity ? )

I know this is all 3rd grade science here. Sorry.
It has to do with Newton's law of uniform motion and inertia. A body in motion, tends to remain in motion, unless acted upon by some external force.
If the truck is full of Styrofoam bowling balls, they possess very little inertia, and at a given velocity, little momentum. Slamming on the brakes is a non-event.
If they're 'real' bowling balls, there's significant inertia and terrific momentum. Slamming on the brakes could be the last thing the driver did.
Filling, and pushing a shopping cart full of each type of ball would really drive the lesson home ( watermelons vs popped corn or cotton balls ?).
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Old 02-03-2023, 02:58 PM   #10 (permalink)
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I place the heavier items in the shopping cart near me, and the lighter stuff at the front, that way I'm not having to accelerate so much mass when turning the cart. Do the opposite and front load the cart, and the rear wheels might skid before the cart wants to turn.

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