Weight Shift at speed (acceleration and braking)

In summary, the weight shifts back and forth depending on the speed of the object. The center of gravity or weight does not move. It is important to create a free body diagram to visualize the movement of the CG.
  • #1
kach22i
51
0
Let's say you have a body in motion, a car, an airplane or hovercraft - does not matter, looking for basic laws of physics here.

1. You know the weight.

2. You know the center of gravity at rest.

3. You know the center of lift (if applicable).

Let's say our object weighs in at 600 lbs.

Lets say our object is going 30 mph.

Q1:
How much does the center of gravity or weight shift back?

Q2:
Lets say I need to start or stop very quickly, how do I calculate the location shift of CG backwards and forwards?

I think the key is taking the the actual weight and turning it into mass, then take into account speed the horizontal force, which in turn may reduce the gravity force or weight over a given time peroid.

An actual example would help, then I can apply it to my situation.
 
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  • #2
I'm not sure I understand you. Say you have a car with known properties and start accelerating at a given rate. Are you looking for how the normal forces on the two axles change due to that acceleration? I suppose you could define an "effective" center-of-mass to be the position where the COM would have to be for the dynamic weight distribution to be the static one.

If this is what you're interested in, you can derive the result once the suspension motions have been damped out by calculating the forces and torques on the vehicle by the ground. The total torque should vanish, and the total force should be ma for a vehicle with mass m accelerating at rate a. If such a vehicle has center-of-mass height h from the ground and wheelbase L, the change in normal force on the front tires can then be shown to be

[tex]
\Delta N_{f}/mg = - h (a/g) /L
[/tex]

You can work out everything else pretty easily from that.
 
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  • #3
Stingray said:
[tex]
\Delta N_{f}/mg = - h (a/g) /L
[/tex]
The car example is getting too complex, my suspension is an air cushion - this should be easier because there are no axles.

I have a hovercraft, but you may want to think of it as a boat on plane or planing if you are more familiar with that.

Even though I used calculations and a pipe to balance the craft, this balance is at static hover, not at speed.

I added too much weight in the back, but how do I determine the center of weight/gravity at speed?

http://www.hoverclubofamerica.org/forum/uploads/1165881286/gallery_181_6_20081.jpg [Broken]
http://www.hoverclubofamerica.org/forum/uploads/1165881286/gallery_181_6_238757.jpg [Broken]

Full thread of project:
http://www.hoverclubofamerica.org/forum/index.php?showtopic=962&st=0 [Broken]
 
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  • #4
Perhaps I've tried to find a universal solution that just does not apply.

Example of what I meant.

Weight Transfer-1
http://www.msgroup.org/TIP074.html [Broken]
When you change speed (accelerate or decelerate) the weight of your motorcycle (including you) shifts in such a way as to put more or less load on your tires. You do not have to weigh the load on your tires to know this with certainty because you can see it happen by observing your front-end 'dive' when you brake.

Stern/rear hovercraft skirt drag might be a version of torque or braking power applied.

1. Car/Motorcyle; weight and center of gravity stay the same unless braking torque is applied or aerodynamic forces have an influenence.

2. Boat; weight and center of gravity are the same until displacement mode is replaced by planing mode, then there is a shift to the "center of lift". This is countered by tabs at the rear which induce drag counterforces and angle changes.

3. Airplane; weight and center of gravity are the same until speed increases lift on the wings causing a shift which is countered by the elevator (typically at the back).

4. Hovercraft; once it's over the "hump speed" which is also a boat term with a slightly diffenerent context, it is in level flight. Weight is centered until torque (paracitic skirt drag) is encountered in the form of wave impact and aerodynamic resistance.
 
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  • #5
kach22i said:
I think the key is taking the the actual weight and turning it into mass, then take into account speed the horizontal force, which in turn may reduce the gravity force or weight over a given time peroid.

An actual example would help, then I can apply it to my situation.

No, the key is drawing a free body diagram.

The CG does not move anywhere. If you found Stingray's words too confusing, try a picture...
 

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  • #6
Thanks......it also take some imagination to visualize not just a line across a body in motion (right/left and front/back), but it's distance above a plane in 3D (up/down).
 

1. What is weight shift at speed?

Weight shift at speed refers to the change in weight distribution of a vehicle as it accelerates or brakes. This change in weight distribution affects the handling and stability of the vehicle.

2. How does weight shift at speed impact vehicle performance?

Weight shift at speed can significantly impact vehicle performance by affecting the balance and traction of the vehicle. It can also impact the responsiveness and control of the vehicle, making it more difficult to handle at high speeds.

3. What factors can contribute to weight shift at speed?

Several factors can contribute to weight shift at speed, including the speed of the vehicle, the rate of acceleration or deceleration, the design and weight distribution of the vehicle, and external forces such as wind or road conditions.

4. How can weight shift at speed be minimized?

Weight shift at speed can be minimized by optimizing the design and weight distribution of the vehicle, as well as using advanced suspension and stability control systems. Properly maintaining tires and ensuring they are at the correct pressure can also help minimize weight shift.

5. What are the potential risks of significant weight shift at speed?

Significant weight shift at speed can increase the risk of losing control of the vehicle and potential accidents. It can also cause uneven wear on tires and affect the longevity of vehicle components such as brakes and suspension systems.

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