Rolling Ball Mechanics: Proving Zero Horizontal Force Constraint

In summary, when a homogenous ball is rolling without slipping on a horizontal plane, the total horizontal force on the ball must be zero. This can be proven by considering the ball as a rigid body and combining the equations for rotation and rolling constraints. If there is only a frictional force acting, the ball will decelerate due to the opposing motion, but the torque produced by this force will cause an increase in rotation rate, which is not possible without slipping. Similarly, if a single horizontal force is applied above the center of the ball, the torque will be too great for the linear acceleration to keep up with the angular acceleration, but by lowering the point of application of the force, it is possible to match the angular and linear acceler
  • #1
Logarythmic
281
0

Homework Statement


Consider a homogenous ball constrained to move on a horizontal plane.
Show that when the ball is rolling without slipping on the plane, then the total horizontal force on the ball must be zero.
HINT: Consider the ball as a rigid body and suitably combine the equations describing the rotation with the rolling constraints.


Homework Equations


None


The Attempt at a Solution


None. Been thinking about this for two days so I need a starter please.
 
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  • #2
Well a good place to start is with the hint and find out what the equations governing its rolling motion are and the conditions for rolling without slipping. So you can bet there's something to do with friction in there aswell.
 
  • #3
I'm not that stupid. ;)
 
  • #4
What exactly are you stuck on then?
 
  • #5
Logarythmic said:

Homework Statement


Consider a homogenous ball constrained to move on a horizontal plane.
Show that when the ball is rolling without slipping on the plane, then the total horizontal force on the ball must be zero.
HINT: Consider the ball as a rigid body and suitably combine the equations describing the rotation with the rolling constraints.


Homework Equations


None


The Attempt at a Solution


None. Been thinking about this for two days so I need a starter please.

If you assume there is only a frictional force acting, then the statement is easily proven. Friction has to oppose the motion of the ball, so if there is any friction the ball will decelerate. However, if this is the only force acting the torque would produce an angular acceleration in the direction of angular motion, so the rotation rate would increase. This cannot happen if there is no slipping, in which case the rotation rate would have to decrease in proportion to the linear velocity.

A similar argument can be made about the application of a single horizontal force at the top of the ball. There is too much torque for the linear acceleration to keep up with the angular accelration. However, the torque can be reduced by lowering the applied force to a point below the top of the ball, so it is possible to match the angular and linear accelerations to have no slipping with a single horizontal force. The point of application to achieve this would be 2/5 of a radius above center. At lower points still above center, a frictional force can provide additonal torque while reducing the linear acceleration, and no slipping can be achieved with a net force acting and a net accelration.

I assume the problem is more restrictive than the application of the forces applied at arbitrary points, and is talking about a single constraining force like friction applied tangent to the ball.
 

1. How does the mass of a rolling ball affect its speed and acceleration?

The mass of a rolling ball primarily affects its acceleration, but not its speed. According to Newton's Second Law of Motion, the force applied to an object is equal to its mass multiplied by its acceleration. Therefore, a ball with a greater mass will require a greater force to accelerate it at the same rate as a ball with a lower mass. However, once the ball is in motion, its speed will not be affected by its mass.

2. What role do friction and air resistance play in the mechanics of a rolling ball?

Friction and air resistance both have a significant impact on the mechanics of a rolling ball. Friction, or the resistance between two surfaces, affects the ball's ability to maintain its velocity and direction. Air resistance, on the other hand, acts as a force opposing the ball's motion, causing it to slow down. Both of these forces can be minimized by using smooth, low-friction surfaces and reducing the ball's surface area exposed to the air.

3. How does the shape of a rolling ball affect its movement?

The shape of a rolling ball can greatly impact its movement. A ball with a round, symmetrical shape will roll smoothly and predictably, while a ball with an irregular shape may bounce or roll in an unpredictable manner. Additionally, the distribution of weight within the ball can affect its stability and ability to maintain its direction of motion.

4. What factors determine how far a rolling ball will travel?

The distance a rolling ball will travel is primarily determined by its initial velocity, the angle at which it is launched, and the amount of friction and air resistance it encounters. The shape and mass of the ball can also play a role, as well as the surface on which it is rolling. A smooth, flat surface will allow the ball to travel further than a rough, uneven surface.

5. How does the height from which a rolling ball is released affect its speed and distance?

The height from which a rolling ball is released can affect its speed and distance in a few ways. First, the potential energy of the ball will increase as it is released from a higher height, which can translate into a higher speed when it reaches the bottom. Additionally, the angle at which the ball is released can impact the distance it travels. A ball released at a steeper angle will travel a shorter distance, while a ball released at a shallower angle will travel a longer distance.

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