Rolling Bottle: Calculating Acceleration of Center of Mass

In summary: Then you will get the right answer -- unless the question was meant to be interpreted in a tricky way, in which case I am missing the trick.In summary, the conversation discusses a problem involving an empty bottle described as a hollow cylinder and a paper with an acceleration a. The goal is to calculate the acceleration of the center of mass. Different equations and methods are shown, but it is important to be consistent about axes in order to get the correct answer.
  • #1
Sonntag
1
0

Homework Statement


There is an empty bottle described as an hollow cylinder, that lies on a paper. Now the paper is pulled with an acceleration a, so that the bottle starts rolling perfectly on the paper. (Have a look at the figure.)

Homework Equations


Calculate the acceleration of the center of mass.

The Attempt at a Solution


Moment of inertia in the center of mass: ##{I_C = 1/2 M R^2}##
Moment of inertia in the center of mass on the surface: ##{I_S = 3/2 M R^2}##
Torque: ##{|\bf{M}| = |\bf{R}| |\bf{F}|}##
Angular acceleration: ##{\alpha = \dfrac{M}{I_S} = \dfrac{F}{3/2 M R}}##
acceleration of the center of mass: ##{a_s = \alpha R = 2/3 \dfrac{F}{M}} ##I have the feeling that my answer isn't the intended of the question. Mistakes? More to do? I hope on your answers and thoughts.
 

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  • #2
Hint: Look at things from the (non-inertial) frame of the paper. (Note also that it's a hollow cylinder, so correct your formula for moment of inertia.)
 
  • #3
Sonntag said:
Moment of inertia in the center of mass: ##{I_C = 1/2 M R^2}##
Moment of inertia in the center of mass on the surface: ##{I_S = 3/2 M R^2}##
I don't understand the expression "Moment of inertia in the center of mass on the surface"
i assume you mean
Moment of inertia about the center of mass: ##{I_C = 1/2 M R^2}##
Moment of inertia about a point on the surface: ##{I_S = 3/2 M R^2}##​
That would be true, as Doc Al points out, for a solid cylinder. But leaving that aside, your method still gave the wrong answer. The reason is that your expression for torque gives the torque about the mass centre. You cannot divide the torque about one axis by the MoI about a different axis to get the angular acceleration.
You can use Doc Al's method, or just be consistent about axes.
 

What is a Rolling Bottle?

A Rolling Bottle is an object consisting of a cylindrical bottle filled with liquid and attached to two wheels or cylinders on either side. It is used as a simple model to study the motion and acceleration of a rolling object.

What is the Center of Mass of a Rolling Bottle?

The center of mass of a rolling bottle is the point at which the weight of the bottle can be considered to be concentrated. In other words, it is the point at which the bottle would balance if suspended from that point.

Why is it important to calculate the acceleration of the center of mass of a Rolling Bottle?

Calculating the acceleration of the center of mass of a rolling bottle allows us to understand and predict the motion of the bottle. This information is useful in various fields such as physics, engineering, and sports.

How do you calculate the acceleration of the center of mass of a Rolling Bottle?

The acceleration of the center of mass of a rolling bottle can be calculated using the formula a = αr, where a is the acceleration, α is the angular acceleration, and r is the radius of the bottle. This formula is derived from Newton's second law, F = ma.

What factors affect the acceleration of the center of mass of a Rolling Bottle?

The acceleration of the center of mass of a rolling bottle is affected by various factors such as the mass of the bottle, the radius of the bottle, the angular acceleration, and the surface on which the bottle is rolling. Other factors such as air resistance and friction may also play a role.

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