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 1d answered What is the physical meaning of reduced mass? 1d comment Can't identify static and kinetic friction regions Are you pulling or pushing on the specimens ?? 1d comment Can't identify static and kinetic friction regions To set the part in motion at an infinitesimal time you are looking at a frictional impulse being applied. I doubt you can measure this. 1d comment Can't identify static and kinetic friction regions Because parts are not rigid it is possible the movement gets initiated by a strain wave along the material. For steel this wave travels at 5000 m/s and so if you have a 1m long specimen the time to unstick is in the order of 1/5000-th of a second. So yes, it is entirely reasonable you are missing it. 1d comment Can't identify static and kinetic friction regions How are you measuring friction? Static friction may occur over such small time period that you might not see it. 1d comment Rotational Dynamics Question What is your question? This appears to be a question someone asked of you to answer. 2d comment How to calculate torque required? Do you know the mass moment of inertia of the pulley, motor and any gear-train attached to it? The dynamics of the system might depend on this a lot. 2d comment How to calculate torque required? This answer would be much better with math formatting. Enclose expressions in dollar signs$...$ for inline or $$...$$ for paragraph style. Then use \frac{a}{b} for fractions like $\frac{a}{b}$. Apr 26 answered When only part of the surface an object is in contact with has friction, what is the normal force I should use? Apr 25 comment Why is the Plane progressive wave equation $y= a\sin (kx-wt)$ for positive direction of x-axis? Find for which $x$ the argument $kx-\omega t$ is zero? It will be $x = \text{(positive)} \,t$ Apr 23 comment Tension and friction. Cool question I agree, a good sketch is 90% of the problem usually. Apr 22 comment Tension and friction. Cool question You might want to mention that contact forces act in equal and opposite fashion on contacting bodies. Apr 22 comment May a point rotate about itself? Please accept whichever answer was most helpful to you. Apr 22 comment May a point rotate about itself? @lucas, Why? Why do points need rotations. To have rotation you need a definition of an orientation. What is the orientation of a point? Also, a location plus orientation is already called a coordinate frame. Apr 21 comment May a point rotate about itself? $0·\infty$ can be anything. Usually we know $v$ and $\omega$ and we calculate $r$. If $\omega=0$ then $r=\infty$. Apr 21 comment May a point rotate about itself? You understand the linear velocities are a vector field. They change value as a function of position. So only at the central axis the value matches between the two cases. Apr 21 comment Friction of a scissor The coefficient of friction is a material property and does not change with geometry. The amount of frictional force changes. Is that what you are asking about? Apr 21 reviewed Approve Friction of a scissor Apr 21 answered May a point rotate about itself? Apr 21 comment Rolling without slipping taking the contact point as pivot Think of the friction force as a function of slip velocity. When slipping is zero friction is zero, otherwise friction acts in a way to minimize slipping.