Recent content by CRJ

Hmm for the quarternion I don't quite get what is got on, will take a look at it (watch some youtube videos) later. Thank you

But α is caused by one force and a is the result of two forces, so is there a relationship between their direction? Or is it just related by the sphere itself (by the circumference etc because the ball roll without slipping) so a is r multiply by α and not cross product of r and α?

If I take r as pointing inwards then it would give me the same result as yours for (r,0) and (-r,0), and for (0,r) r is downwards(y), α out of the paper (z) and a would be to the left (x) and hence negative

Erm if I take r as pointing out radially from center of the sphere then at (r,0) r to the right(x), α positive pointing out of the paper (z) would give me a downwards (y) hence negative. At (-r,0) r to the left(x), α positive pointing out of the paper (z) would give me a upwards (y) hence...

Sorry for the late reply, I was quite busy doing lectures and tutorials for the past few days and didn't really have time. I asked my physics lecturer and he said that ω&α are vectors but they are complicated so it is not yet covered. So for cross multiplication the direction of the vector is...

So net acceleration should be negative since net force is negative and angular acceleration is due to friction force which is positive so it should be positive? So is the angular velocity negative thats why the angular velocity and acceleration have different signs, they are opposite so the...

hmm. r should be positive since it is the radius and cannot be negative, and r is a constant since it is the radius of the sphere. a and α should be negative since the sphere decelerates (slows down). so it would be a=r×α or -a=r×(-α)? I am concerned because if it is done the other way(taking...

I think I understand what you are saying, and I can get the same answer. Is this correct? (I think angular velocity is clockwise and mg will cause an anticlockwise moment, so angular acceleration will be negative)

Erm I a bit confused about the sign, like the ans given by Chegg would suggest the solution above. I don't quite get it, they probably do this so that the direction are the same. but if I actually change it to this, it would give me the same answer too. Would this be better? Like the force for...

Ohh I previously thought that torque is about the centre of the loop, I thought its the motion around the loop. So it is actually torque about the centre of mass and accounts for the rotation of the object as it roll up the loop? so small r should be used for the whole equation, and there is no...

Is this FBD correct?

Thank you so much for your help, it is true that I previously didn't consider the friction force (upwards) So I actually got an answer from Chegg and turns out it is correct (got a classmate to try it) But I dont fully understand the solution. So there is an upward friction force to be...

Thank you for your reply I think I do know a bit as in the relationship between angular and linear velocity, acceleration. I also know that there has to be static friction (not kinetic friction as it is not slipping) as the sphere moves, and it is there but there is no work done by friction as...

Thank you for your reply True, I am not quite sure of which r to use actually. So does it mean that vertical force should be negative since it is slowing down? I am not quite sure for FBD, is there a component of the normal force acting upwards? Shouldn't normal force act perpendicular to the...

Thank you for your reply I am not really sure about what the directions in red fonts mean by using newtons second law, but I did use τ=Iα for rigid body and the relation for rolling without slipping aCM= r×α.