# ABS system on a two-wheeled vehicle - Conservation of Angular Momentun

• engineerslovephysics
In summary: When counter-steering, does the change in the center of gravity relative to the wheels cause the bike to go where you want it to go? Obviously, traditional steering will not work at high speeds and will prompt you to go the opposite way you intended to steer (hence counter-steer).Yes, the change in center of gravity causes the bike to go in the direction you're steering it.
engineerslovephysics
Hello,

The question I have pertains to conservation of Angular momentum on a motorcycle. I know that the dynamic friction is less than the static friction, so when you are braking on a (say a motorcycle) and the wheels lock up, the bike is bound to fall over. This is the reason ABS (Anti-lock braking) has been invented. My question is does the reason the vehicle falls over only due to the fact that Angular momentum comes to zero when the wheels angular velocity equals zero? If that is the case, doesn't ABS prevent the wheel from locking up only to keep the wheels gyroscopic ability?

This question has been bugging me for some time and I am a little confused, thanks.

Welcome to the PF.
engineerslovephysics said:
My question is does the reason the vehicle falls over only due to the fact that Angular momentum comes to zero when the wheels angular velocity equals zero?
No. When the front wheel locks up, you can't steer anymore, so the front end washes out and down you go. If only the back wheel locks up and you can still steer, you may be able to come to a stop without falling, but that takes a bit of skill usually.

engineerslovephysics
What is related to the angular momentum is the torque (force), the torque will keep you balanced on the track...
let's say you slow down with your bike until zero of velocity so the torque will decrease and then the bike fall down.
The concept of ABS is not exactly what you mentioned but to prevent the sudden change in the system so instead to convert the inertia force heavily on the breaks, you reduce it slightly as much as possible in short time intervals, so the reaction of the system (Bike in this case) will be smooth.

engineerslovephysics
We are told that a bicycle wheel has angular momentum and gyroscopic torque keeps the bike upright. Well, it does, but that isn’t the whole story. For example, we can ride bikes at slow speed when the angular momentum is very small, or circus performers can ride tiny bikes with tiny wheels that have negligible angular momentum.

What really keeps us upright most of the time is our own feed back. Think about how at slow speed you often are working the handlebars quite a lot. If the bike starts to tip to the right, we steer to the right. The rolling wheel means that the frictional force in the plane of rotation doesn’t get transferred to the bike. The component of the frictional force perpendicular to the plane pushes the bottom of the wheel to the right standing the bike back up.

However, if the front wheel skids, the rolling no longer negates the force of friction in the plane. The sliding friction points opposite the direction of motion no matter which way we turn the front wheel and we lose our ability to correct tilts by steering.

engineerslovephysics and berkeman
Cutter Ketch said:
We are told that a bicycle wheel has angular momentum and gyroscopic torque keeps the bike upright.
When hands free, the gyroscopic torque on the front wheel can steer a bicycle into the lean, which contributes to self stability. But this is not the whole story.

Cutter Ketch said:
What really keeps us upright most of the time is our own feed back. Think about how at slow speed you often are working the handlebars quite a lot. If the bike starts to tip to the right, we steer to the right. The rolling wheel means that the frictional force in the plane of rotation doesn’t get transferred to the bike. The component of the frictional force perpendicular to the plane pushes the bottom of the wheel to the right standing the bike back up.
berkeman said:
Welcome to the PF.
No. When the front wheel locks up, you can't steer anymore, so the front end washes out and down you go. If only the back wheel locks up and you can still steer, you may be able to come to a stop without falling, but that takes a bit of skill usually.
Thanks!

Aah, which is where counter-steering comes into play. When I am on my motorcycle, I always wonder how counter steering works (hey it works, who am I to complain to?) and why I have to lean into corners when turning at high speeds (what you see in Moto GP races). When counter-steering, does the change in the center of gravity relative to the wheels cause the bike to go where you want it to go? Obviously, traditional steering will not work at high speeds and will prompt you to go the opposite way you intended to steer (hence counter-steer). If one could elaborate on this, I'd appreciate it much.

Thanks,

engineerslovephysics said:
When I am on my motorcycle, I always wonder how counter steering works

engineerslovephysics

## 1. What is the purpose of the ABS system on a two-wheeled vehicle?

The ABS (Anti-lock Braking System) on a two-wheeled vehicle is designed to prevent the wheels from locking up during braking, which can cause loss of control and potential accidents. It helps the rider maintain steering control and stability while braking, especially on slippery or uneven surfaces.

## 2. How does the ABS system work?

The ABS system uses sensors to detect the speed of each wheel. If the system detects that a wheel is about to lock up, it will release the brake pressure on that wheel, allowing it to rotate freely. This process is repeated multiple times per second, preventing the wheels from skidding and maintaining traction.

## 3. Why is conservation of angular momentum important for the ABS system?

Conservation of angular momentum is important for the ABS system because it allows the wheels to rotate freely while the vehicle is still in motion. This helps to maintain stability and control during braking, as well as preventing the wheels from locking up and causing accidents.

## 4. Can the ABS system be turned off?

In most cases, the ABS system cannot be turned off on a two-wheeled vehicle. This is because it is a safety feature that helps prevent accidents. However, some motorcycles may have a switch or button that allows the rider to disable the ABS system, but this is not recommended unless absolutely necessary.

## 5. Are there any limitations to the ABS system on a two-wheeled vehicle?

While the ABS system is a valuable safety feature, it does have some limitations. It may not be effective on extremely slippery surfaces such as ice or gravel, and it may not prevent accidents caused by excessive speed or aggressive riding. It is important for riders to still use caution and good judgment while operating a two-wheeled vehicle with ABS.

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