Hello, thank you for this example. It was very helpful in teaching rotational kinematics to class. I do have 2 suggestions, which came up during class discussions: (i) Vcom >= R omega, since omega can be zero during the slide (if no rotation), but the Vcom will not be zero since the ball is sliding (com moving towards the pins). (ii) Once the ball starts rolling, the friction is static and is helping the movement by causing the ball to roll; the friction constant should also be static.
two points: . Vcm > Rw (not the opposite) . Without inserting values for initial velocity and friction, one can calculate the final (rolling) speed as 5/7th the initial speed, as both friction coefficient and constant of gravity cancel out.
Hey Physics Ninja! This video was very informative and helpful! I was wondering, what happens if you have an initial angular velocity that is not 0. For example, a bowler gives the ball spin on release. Would it be possible to factor in additional stuff to the formulations? I am very interested in understanding more from a more complex situation.
at ~14:00 i write down the kinematics for the rotation and set w0=0 for my case. If you put an initial spin w0 is NOT equal to 0 anymore. If will be either positive or negative depending if there is front spin of back spin. Note that the addition of spin does not change the dynamics (forces and torques), it will only affect the kinematics.
I think you made a mistake with the sign in 4:40? V_{cm} is greater than R*w. The velocity will decrease because of friction while the angular velocity increases. This makes sense as initially you don't have angular velocity, but you have linear velocity. It doesn't really affect the solution but thought of pointing it out
Thank you so much, this was so, so helpful! I just have a quick question about the unit for angular acceleration: why is it 1/(s^2) and not rad/(s^2) when using the equation (5*coefficient of friction*g)/(2r)? Does it have something to do with radians being a dimensionless quantity?
I had the question some 25 years ago. If you think about a radian it’s really dimensionless. Think about using trig to find an angle. Sin(theta)= opp/ hyp. Clearly the right hand side is dimensionless. So the left hand side is also dimensionless. Arc sin to find theta must have be dimensionless. Another simple example is c=2*pi*r. You might say 2*pi has units of radians but the circumference equation still has to hold. Radians is really just a ratio and not a “strict” unit like seconds or meters. At least that’s how I understand it.
@@PhysicsNinja Got it, that makes sense, and thank you so much for the quick response and explanation! I always get confused when considering the unit of quantities involving radians, but your video and response really helped clear up those confusions so thank you so much!!
Ok so once a pure roll starts does it theoretically keep rolling forever if it was say on an infinitely long bowling lane? What role does the force of friction play once the pure roll starts? I'm not sure.
What I don't understand: if accel_x = -coeff * g, doesn't that mean acceleration is a constant? I don't understand how that works, after all, once the bowling ball is stopped, accel_x 'should' become 0, right? *edit it's probably because the 'minus' becomes a plus once it 'reverses', but since it never really reverses, it's probably going to end up being 'between minus and plus' == standing still? I'm having some philosophical problems with all this but alas :P
You’re right that once it stopped the acceleration is 0 but remember that at that point you would no longer have kinetic friction, so your problem has changed.
A ball with an initial velocity of 6ft/s is rolling on a flat plane without slipping. The ball has traveled some distance before slowing down how far the ball has been traveling when it comes to a complete stop?
So is the ball still spinning before a pure roll starts... Like before the pure roll the torque from the friction causes an angular acceleration in the ball ... The force of friction also causes the ball to slow down... Once the wr of the ball catches up with the speed of the cm of the ball then the pure roll starts since that is the condition of a pure roll. Please let me know if my understanding is accurate...
I have a doubt The real life in bowling lane, the person throw the ball to the lane... When instand the ball touch the lane, the Vo could considered O m/s?? Or the ball has a Vo produced by the kinetics and potential energy
Bowlers actually break ball roll into 3 phases skid, hook, and roll. It makes me so happy to see someone put this much thought into analyzing physics in bowling. Looking forward to bingeing out on your other videos.
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There are two types of sliding. One is called slipping when Vcm < R*Omega another is skidding when Vcm > R*Omega. So the dropped ball is skidding.
So useful, glad you do harder problems like these! Other videos are just introductions so this really helps
I have been in trouble with this kind of questions. Really thanks a lot!
What would the equation of motions be if there an initial rotation perpendicular to the linear velocity?
Thank you, Sir.
Is it possible to solve the problem of obtaining S using conservation of Energy?
The reason why the bowling ball slides is because of the oil on the lane.
I agree
Awesome!
Hello, thank you for this example. It was very helpful in teaching rotational kinematics to class. I do have 2 suggestions, which came up during class discussions:
(i) Vcom >= R omega, since omega can be zero during the slide (if no rotation), but the Vcom will not be zero since the ball is sliding (com moving towards the pins).
(ii) Once the ball starts rolling, the friction is static and is helping the movement by causing the ball to roll; the friction constant should also be static.
Why isn’t alpha negative? It is increasing rolling speed in negative direction.
two points:
. Vcm > Rw (not the opposite)
. Without inserting values for initial velocity and friction, one can calculate the final (rolling) speed as 5/7th the initial speed, as both friction coefficient and constant of gravity cancel out.
True, V_cm > Rw when sliding. It is obviously a typo since he said initially w = 0.
Hey Physics Ninja! This video was very informative and helpful! I was wondering, what happens if you have an initial angular velocity that is not 0. For example, a bowler gives the ball spin on release. Would it be possible to factor in additional stuff to the formulations? I am very interested in understanding more from a more complex situation.
at ~14:00 i write down the kinematics for the rotation and set w0=0 for my case. If you put an initial spin w0 is NOT equal to 0 anymore. If will be either positive or negative depending if there is front spin of back spin. Note that the addition of spin does not change the dynamics (forces and torques), it will only affect the kinematics.
I think you made a mistake with the sign in 4:40? V_{cm} is greater than R*w. The velocity will decrease because of friction while the angular velocity increases. This makes sense as initially you don't have angular velocity, but you have linear velocity. It doesn't really affect the solution but thought of pointing it out
Thank you so much, this was so, so helpful! I just have a quick question about the unit for angular acceleration: why is it 1/(s^2) and not rad/(s^2) when using the equation (5*coefficient of friction*g)/(2r)? Does it have something to do with radians being a dimensionless quantity?
I had the question some 25 years ago. If you think about a radian it’s really dimensionless. Think about using trig to find an angle. Sin(theta)= opp/ hyp. Clearly the right hand side is dimensionless. So the left hand side is also dimensionless. Arc sin to find theta must have be dimensionless. Another simple example is c=2*pi*r. You might say 2*pi has units of radians but the circumference equation still has to hold. Radians is really just a ratio and not a “strict” unit like seconds or meters. At least that’s how I understand it.
@@PhysicsNinja Got it, that makes sense, and thank you so much for the quick response and explanation! I always get confused when considering the unit of quantities involving radians, but your video and response really helped clear up those confusions so thank you so much!!
1 hour before my phys115 final wheeeeeew
Daniel Li Ge how’d you go
@@in51ght67 haha I'd like to know too
Ok so once a pure roll starts does it theoretically keep rolling forever if it was say on an infinitely long bowling lane? What role does the force of friction play once the pure roll starts? I'm not sure.
Yes it would keep rolling forever, on earth it does not happen due to air resistance and such.
this was incredibly helpful, thank you very much!!
What I don't understand: if accel_x = -coeff * g, doesn't that mean acceleration is a constant? I don't understand how that works, after all, once the bowling ball is stopped, accel_x 'should' become 0, right?
*edit it's probably because the 'minus' becomes a plus once it 'reverses', but since it never really reverses, it's probably going to end up being 'between minus and plus' == standing still? I'm having some philosophical problems with all this but alas :P
You’re right that once it stopped the acceleration is 0 but remember that at that point you would no longer have kinetic friction, so your problem has changed.
@@PhysicsNinja good point :) great video btw, really helped me out!
Thank you sir
A ball with an initial velocity of 6ft/s is rolling on a flat plane without slipping. The ball has traveled some distance before slowing down how far the ball has been traveling when it comes to a complete stop?
So is the ball still spinning before a pure roll starts... Like before the pure roll the torque from the friction causes an angular acceleration in the ball ... The force of friction also causes the ball to slow down... Once the wr of the ball catches up with the speed of the cm of the ball then the pure roll starts since that is the condition of a pure roll. Please let me know if my understanding is accurate...
Yes, you got it
@@PhysicsNinja thanks so much
thank you very much sir
I have a doubt
The real life in bowling lane, the person throw the ball to the lane... When instand the ball touch the lane, the Vo could considered O m/s?? Or the ball has a Vo produced by the kinetics and potential energy
ur amazing ty
Ridiculously helpful, thanks times a million💗
what is the velocity of the bowling ball and pin right after the collision?
You didn't account for the 10-pin
YOU ARE A LIFESAVER!! THANK YOU SO MUCH!
Thank you, this helped a lot.
Thanks
Bowlers actually break ball roll into 3 phases skid, hook, and roll. It makes me so happy to see someone put this much thought into analyzing physics in bowling. Looking forward to bingeing out on your other videos.