How does friction affect trains?
The static frictional force on the train is between the wheels and the track. The only way would be to just overcome a large frictional force would be to get one car moving at at time. Once a car is moving, the axle-wheel interaction changes to kinetic friction with a lower coefficient.
Is there any friction between the wheels of train and iron rail?
Yes, there is always friction between a moving train’s wheels and the iron rails. Because the wheels are rolling on the track, this friction is known as rolling friction.
What causes lack of adhesion between a wheel and a rail?
Toppling conditions Toppling will occur when the overturning moment due to the side force (centrifugal acceleration) is sufficient to cause the inner wheel to begin to lift off the rail. This may result in loss of adhesion – causing the train to slow, preventing toppling.
How does a train keep traction?
Trains get traction because of the immense weight of the locomotives, and the friction generated between the wheel and rail head. Furthermore, the free rolling bearings on rolling-stock significantly contribute to momentum keeping the train rolling.
Do trains still use sand?
Sanding is used in train operations to improve adhesion in both braking and traction. It usually occurs automatically when the train driver selects emergency braking. Sanding in traction, however, is a manual process. The train driver must determine when to apply the sand and how long the application should last.
What is the force of a moving train?
First, a force of 2 to 5 pounds per ton of train weight is required to move on straight level track. At very slow yard speeds only 2 to 3 pounds is needed while increasing to about 5 pounds at higher speeds. This force is required to overcome bearing friction, rail deflection, minor flange contact, etc.
Is there a force of friction between the wheels?
Yes, rolling force works between the wheels and iron nails. The friction between these will decrease if a cushion will be introduced between them.
What keeps train wheels from slipping?
The wheels on each side of a train car are connected with a metal rod called an axle. This axle keeps the two train wheels moving together, both turning at the same speed when the train is moving. To help the wheels stay on the track their shape is usually slightly conical.
What does sanding do on trains?
Sanding is used in train operations to improve adhesion in both braking and traction. In braking it is used to ensure that the train stops in as short a distance as possible. It usually occurs automatically when the train driver selects emergency braking. The sand is supplied from a hopper mounted under the train.
Why do trains need sand?
A train operator will press a button to have sand sprayed in front of the wheels. The coarse sand provides extra traction helping the train stop in time. The train’s traction control can also kick in automatically when the onboard computers sense that the train’s wheels are slipping.
What turns the wheels on a train?
The wheels on each side of a train car are connected with a metal rod called an axle. This axle keeps the two train wheels moving together, both turning at the same speed when the train is moving. This is where the wheels’ geometry comes in. To help the wheels stay on the track their shape is usually slightly conical.
How does friction prevent a train from sliding?
Sliding is prevented by friction and the friction force is equal to the product of the weight – the perpendicular force – and the dimensionless coefficient of static friction. The coefficient of static friction between steel and steel can be as high as 0.78 so the angle would have to be hugely non-horizontal for the train to slide.
Why is friction between wheel and rail important?
The friction between wheel and rail has a major impact on maintenance and logistics because it determines the wheel and rail wear, in case it is too high, and reduces the ability to brake and to accelerate properly, in case friction is too low.
How does a train get traction on level ground?
Trains have very little friction between the wheel and the rail-head, thus, allowing trains to move at quicker speeds on level ground than cars, which have rubber tires, thus, aerodynamic drag is greatly increased. Contrary to popular belief, the surface of the wheel that makes contact with the rail-head is merely the size of a small coin.
How are the wheels on a train different?
Train wheels aren’t perfect cylinders. They’re beveled to make them wider on the inside. This means that when the train shifts left or right on the track, the diameter of the wheels can change. But because the wheels are connected by an axle, they still spin at the same rate.