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1h
comment Diagonal of a thin rectangular foil, inertial principal axis?
Is the foil on the xy axis? You need to define your coordinate systems and orientations?
3h
comment Do you say it right?
Hence the difference in customary units and scientific units. My weight in customary units is in pounds, stones, kilograms, etc. My weight in scientific units is in pounds-force or Newton.
Feb
5
comment To prove uniqueness of the rotation tensor associated with rotation of a rigid body
I read your last line which says: "Now, I am not sure how to prove that $\overline{\overline {R}}_{lk}=\overline{\overline {R}}_{ji}$. And this is where I needed help".
Feb
4
comment Free body diagram with forces of friction
Don't worry about the direction of friction. If in the end the result is negative, just flip the direction.
Feb
4
comment Transfer of angular momentum during oblique impact with(out) adhesion
See this accepted answer for how to handle friction in contacts. For spheres, things simplify quite a bit.
Feb
4
comment To prove uniqueness of the rotation tensor associated with rotation of a rigid body
You are really asking, Why are rigid body rotations orthonormal such that $R^{-1} = R^\intercal$. This is the point you are stuck at, and you need to show this in the title, otherwise it confuses the reader.
Feb
2
comment Science question
So what is your question? This look like "hey do my homework for me" type of question and it is likely to be closed.
Feb
1
comment Calculate the loss of kinectic energy during this collision
Welcome to Physics. Here you can ask your questions, but avoid posting homework assignments. So what is your question in this problem you are tasked to answer.
Jan
31
comment Tension in rods (basics)
Is there any friction on the ground?
Jan
31
comment Tension in rods (basics)
You can ignore the floor, and just assume the left and right corners are on rollers (with friction maybe). Or are they pinned? Hmm, difficult to ascertain from the diagram.
Jan
31
comment What forces act on a caravan being towed by a car?
On a straight road with constant speed, the only additional forces are that of air resistance. But I suspect you are asking for more that this. So please add more details because at this point the question is too broad.
Jan
31
comment Tension in rods (basics)
You need to add the forces (if any) on the bottom rod also.
Jan
31
comment Predicting contact time and COR (coeff of restitution) for a cricket ball and pitch
COR is empirically derived, unless you want to do the quantum mechanics of molecular bond strain.
Jan
31
comment Predicting contact time and COR (coeff of restitution) for a cricket ball and pitch
It is because in mechanics it is all about geometry and without a sketch people have no idea what you are talking about.
Jan
29
comment Acceleration in a non-inertial reference frame
If no friction then what forces are acting on the ball? Gravity and the tension of the yard. So what would make the ball change its constant rotation about the z-axis?
Jan
27
comment Predicting contact time and COR (coeff of restitution) for a cricket ball and pitch
You might to explain what a pitch, spinner etc is.
Jan
27
comment equation for velocity vs displacement for nonlinear acceleration
So my answer was useful. Great.
Jan
26
comment Predicting contact time and COR (coeff of restitution) for a cricket ball and pitch
The mechanics are WAY more complicated than what you can put into a COR. Look at a tennis ball hit at 6000fps (youtube.com/watch?v=VHV1YbeznCo).
Jan
26
comment Off-center impulse equations
For a graphical solution to the two centered spheres collision look at physics.stackexchange.com/a/220776/392
Jan
26
comment Off-center impulse equations
I have a similar answers here physics.stackexchange.com/a/155431/392 and physics.stackexchange.com/a/29160/392