Speed refers to the rate at which an object is moving, while velocity takes into account both the speed and direction of motion. In a subway train, the speed would be measured in kilometers per hour, while the velocity would also include the direction the train is moving, such as north or south.
Newton's first law of motion states that an object will remain at rest or in motion at a constant velocity unless acted upon by an external force. In the case of a subway train, the train will continue to move at a constant velocity unless a force, such as friction or the brakes, is applied to slow it down or bring it to a stop.
The weight of a subway train, which is the force of gravity acting on the train, can affect its acceleration. A heavier train may require more force to accelerate or decelerate, while a lighter train may require less force. However, the design and power of the train's engine also play a significant role in its acceleration.
Friction and air resistance can both act as external forces that can slow down or affect the movement of a subway train. Friction can occur between the train and the tracks, while air resistance can occur as the train moves through the air. These forces can impact the train's speed, acceleration, and overall movement.
Momentum is a measure of an object's mass and velocity. In the case of a subway train, its length can affect its momentum by contributing to its mass. A longer train would have a greater mass and therefore a greater momentum, which can impact its ability to start, stop, or change direction. However, other factors such as the speed and power of the train also play a significant role in its momentum.