Vector Mechanics — Double Gear Rolling on a Rack

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Homework Help Overview

The discussion revolves around the mechanics of a double gear rolling on a stationary rack, specifically focusing on the relationship between the linear displacement of point A and the angular displacement of the gear. Participants are exploring the equation relating these quantities and the definitions of radians in this context.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to understand the derivation of the equation ##\frac {x_A} {2πr_1} = -\frac {θ} {2π}## and are questioning the definition of ##\theta## in relation to the problem. There are discussions about how far point A moves for different angular displacements and the connection between radians and arc length.

Discussion Status

The conversation is ongoing, with some participants providing insights into the definitions of radians and the movement of point A. There is a lack of response from the original poster, which has been noted by others. Multiple interpretations of the problem are being explored, particularly regarding the relationship between linear and angular motion.

Contextual Notes

Participants are working under the constraints of a homework assignment, which may limit the information available and the assumptions that can be made. There is an emphasis on understanding the underlying concepts rather than reaching a final solution.

Alexanddros81
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Homework Statement
The double gear shown rolls on the stationary lower rack; the velocity of its
center A is 1.2 m/s directed to the right. Determine (a) the angular velocity
of the gear, (b) the velocities of the upper rack R and of point D of the gear.
Relevant Equations
-
Hi!
My first question: How does he get the equation ##\frac {x_A} {2πr_1} = -\frac {θ} {2π}## ?
 

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You forgot to define ##\theta## (Solution forgot it too !)
Ask youriself: how far does ##A## go to the right for one revolution (##\theta = 2\pi##) ? For half a revoluton ? For a given ##\theta ## ?
 
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Alexanddros81 said:
Homework Statement:: The double gear shown rolls on the stationary lower rack; the velocity of its
center A is 1.2 m/s directed to the right. Determine (a) the angular velocity
of the gear, (b) the velocities of the upper rack R and of point D of the gear.
Relevant Equations:: -

Hi!
My first question: How does he get the equation ##\frac {x_A} {2πr_1} = -\frac {θ} {2π}## ?
What is the definition of a radian? How is it connected to this question?
 
Chestermiller said:
What is the definition of a radian? How is it connected to this question?

A radian is ratio between length of the arc and its radius:

$$\theta = \frac {x} {r}$$

For a complete circle, it became:

$$\theta = \frac {2 \pi r} {r} \\
\theta = 2 \pi ~ \text {rad}$$
 
bagasme said:
A radian is ratio between length of the arc and its radius:

$$\theta = \frac {x} {r}$$

For a complete circle, it became:

$$\theta = \frac {2 \pi r} {r} \\
\theta = 2 \pi ~ \text {rad}$$
I was asking the OP to help him/her understand where the equation in question had come from.
 
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But we got no reaction whatsoever from @Alexanddros81 -- not so nice !
 
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Hi!
I will provide my thinking soon for this question
 
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BvU said:
You forgot to define ##\theta## (Solution forgot it too !)
Ask youriself: how far does ##A## go to the right for one revolution (##\theta = 2\pi##) ? For half a revoluton ? For a given ##\theta ## ?

for one revolution ##A## goes to the right ##2\pi r_1##. For half a revolution ##\pi r_1##.
For a given ##\theta## goes to the right ##\theta r_1##?
 
Alexanddros81 said:
For a given ##\theta## goes to the right ##\theta r_1##
No. Theta is an angle. It does not go to the right. You mean: For a given ##\theta##, A goes to the right ##\theta r_1##. Correct.

Now think the lower rack out of the way. Le A be a fixed axis
Ask youriself: how far does B (rack R) go to the right wrt A for one revolution (##\theta=2\pi##) ? For half a revoluton ? For a given ##\theta## ?
 

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