Hi, at the last step, you put inertia value which has kg and the output is N.m. Shouldn't we convert kg to N while passing to the torque calculation? thanks for the video
Hi Joshua. very good video. i learned much. i hv a question. if the disk is not thin but has 3 inches thickness. and is holliw inside. what is the moment of inertia? thanks.
What is the torque needed to stop a disk's rotation from rpm to 0 rpm in 1s (depending on how fast you want it to stop)? I think the required torque is greater than 2Nm.
If I have a vertical shaft with 2 more disks fixed to it and evenly distributed how can I find the torque needed to rotate the shaft along with the disks considering all the possible variables in a real life scenario.
If the disks are attached to the shaft, then there is no difference from the example given: use the sum of the moments of inertia of the two disks as the total system moment of inertia.
The gravitational torque on this disk would be zero because it is symmetric, so the force of gravity passes through the axis and therefore has zero lever arm regardless of the orientation of the disk. So for this problem, no the orientation of the disk relative to the local gravitational vector doesn’t matter.
@@joshuacolwell Thanks for confirming that. I am making a turntable for product photography and I found your video super-useful for calculating the torque required to spin a 1m diameter 15mm thick plywood disk to 10rpm in 3 seconds so I could choose the an appropriate dc motor (most likely with an attached gearbox) to direct drive the disc. The disc is about 5.7kg so the torque works out to be 0.1529 Nm.
@@arisskarpetis hi aris. how r u able to calculate the torque or ur moment of inertia since ur plywood has 15mm thickness? what if the thickness is 3 inches? thanks. ;) also how do we compute if its hollow inside with only d sides fully covered? thanks
This example works out the net torque that must be applied to the disk. If there is friction, then the motor torque minus the frictional torque equals I times alpha. We have enough information to calculate I and alpha, but we would need additional information to calculate the frictional torque, such as the torque applied by the motor. With the information provided we can only calculate the net torque.
Torque changes the angular momentum of an object which means usually that it is changing the rate of rotation. If you know the value of mass radius and angular velocity in revolutions per minute then you can calculate the angular momentum of some thing. But that doesn’t tell you anything about any torque acting on the object you need some other information to know how the angular momentum is changing in order to determine the torque.
Another way to look at it is by dimensional analysis: torque has units of force times distance, which means it has time squared in the denominator. The quantities you mention are distance, mass, and angular rotation rate, which just has one time in the denominator. So, again, you would need two values of rpm (start and finish) and the time interval between them, as one example, to calculate the torque to give that change in angular momentum.
if time is involved in the equation, then no matter how long it takes to accelerate, the disk will always arrive at the speed that any motor can reach, yes or no?
I’m not sure I understand the question. Final speed depends on acceleration and duration (time) of acceleration. Alternatively, from an energy standpoint, final speed depends on initial speed and the amount of energy put into the system through a torque.
@@joshuacolwell what would happen if the motor could not have enough torque to accelerate the disc ? Would it take longer to accelerate at some specific velocity, or the rpm of the disc would decrease ?
No problem I'm just really greatfull you made this video I have to submit an assignment tomorrow it's 12:08am in india and I can only complete my assignment bc of u.
Thankyou so much for making this video!
Great video! How would i calculate the torque at stall when spinning continuously?
What if the mass isnt connected to the shaft, and balanced in between parallel shafts.
Hi, at the last step, you put inertia value which has kg and the output is N.m. Shouldn't we convert kg to N while passing to the torque calculation? thanks for the video
Hi Joshua. very good video. i learned much. i hv a question. if the disk is not thin but has 3 inches thickness. and is holliw inside. what is the moment of inertia? thanks.
The thickness doesn’t matter, but if it is hollow, the moment of inertia is MR^2.
Good one🤘🤘..what if I have motor producing torque of 2 Nm ..so to stop motor instantly would I require 2 Nm braking torque??? Please reply soon
What is the torque needed to stop a disk's rotation from rpm to 0 rpm in 1s (depending on how fast you want it to stop)? I think the required torque is greater than 2Nm.
If I have a vertical shaft with 2 more disks fixed to it and evenly distributed how can I find the torque needed to rotate the shaft along with the disks considering all the possible variables in a real life scenario.
If the disks are attached to the shaft, then there is no difference from the example given: use the sum of the moments of inertia of the two disks as the total system moment of inertia.
@@joshuacolwell Thanks a lot !
Does it make any difference if the plane of rotation is parallel or perpendicular to the ground?
The gravitational torque on this disk would be zero because it is symmetric, so the force of gravity passes through the axis and therefore has zero lever arm regardless of the orientation of the disk. So for this problem, no the orientation of the disk relative to the local gravitational vector doesn’t matter.
@@joshuacolwell Thanks for confirming that. I am making a turntable for product photography and I found your video super-useful for calculating the torque required to spin a 1m diameter 15mm thick plywood disk to 10rpm in 3 seconds so I could choose the an appropriate dc motor (most likely with an attached gearbox) to direct drive the disc. The disc is about 5.7kg so the torque works out to be 0.1529 Nm.
@@arisskarpetis hi aris. how r u able to calculate the torque or ur moment of inertia since ur plywood has 15mm thickness? what if the thickness is 3 inches? thanks. ;) also how do we compute if its hollow inside with only d sides fully covered? thanks
The textbook tittle and author please
How would you find the frictional torque??
This example works out the net torque that must be applied to the disk. If there is friction, then the motor torque minus the frictional torque equals I times alpha. We have enough information to calculate I and alpha, but we would need additional information to calculate the frictional torque, such as the torque applied by the motor. With the information provided we can only calculate the net torque.
Is it supposed to be 10 x10^-3 ? 10^-3 is a different number
Hello sir..can we calculate torq if we only know m,r,and rpm only..
Torque changes the angular momentum of an object which means usually that it is changing the rate of rotation. If you know the value of mass radius and angular velocity in revolutions per minute then you can calculate the angular momentum of some thing. But that doesn’t tell you anything about any torque acting on the object you need some other information to know how the angular momentum is changing in order to determine the torque.
Another way to look at it is by dimensional analysis: torque has units of force times distance, which means it has time squared in the denominator. The quantities you mention are distance, mass, and angular rotation rate, which just has one time in the denominator. So, again, you would need two values of rpm (start and finish) and the time interval between them, as one example, to calculate the torque to give that change in angular momentum.
if time is involved in the equation, then no matter how long it takes to accelerate, the disk will always arrive at the speed that any motor can reach, yes or no?
I’m not sure I understand the question. Final speed depends on acceleration and duration (time) of acceleration. Alternatively, from an energy standpoint, final speed depends on initial speed and the amount of energy put into the system through a torque.
@@joshuacolwell what would happen if the motor could not have enough torque to accelerate the disc ? Would it take longer to accelerate at some specific velocity, or the rpm of the disc would decrease ?
I just realized my “d” looks like an “alpha”.
No problem I'm just really greatfull you made this video I have to submit an assignment tomorrow it's 12:08am in india and I can only complete my assignment bc of u.