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Does a spin around axis not passing through COM ever stop?
Clash Royale CLAN TAG#URR8PPP
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Suppose the rod is in space and I apply equal but opposite forces at both ends momentarily. The rod starts spinning around COM and I believe it should keep spinning forever because the COM is not accelerating and angular momentum has to be conserved. No issues in this case.
Next suppose I move the axis of rotation away from the COM, say, to 1/3rd from one end by pinning it,; then apply equal but opposite force at both ends momentarily. What happens now ? Would the rod keep spinning forever ? If yes, wouldn't this mean that the COM is accelerating ? If no, wouldn't this mean that the angular momentum is not conserved ?
angular-momentum
asked 4 hours ago
rsadhvika
28218
 |Â
show 5 more comments
up vote
1
down vote
favorite
Suppose the rod is in space and I apply equal but opposite forces at both ends momentarily. The rod starts spinning around COM and I believe it should keep spinning forever because the COM is not accelerating and angular momentum has to be conserved. No issues in this case.
Next suppose I move the axis of rotation away from the COM, say, to 1/3rd from one end by pinning it,; then apply equal but opposite force at both ends momentarily. What happens now ? Would the rod keep spinning forever ? If yes, wouldn't this mean that the COM is accelerating ? If no, wouldn't this mean that the angular momentum is not conserved ?
angular-momentum
asked 4 hours ago
rsadhvika
28218
How are you going to move the axis of rotation? That might answer your question. Also, remember Newton's first law.
– Aaron Stevens
4 hours ago
@AaronStevens you've been my life saver today! ty again :) I think I can just nail the rod 1/3rd away from one end and give a little momentary torque so that it starts spinning ?
– rsadhvika
4 hours ago
schoolphysics.co.uk/age11-14/Mechanics/Statics/text/…
– rsadhvika
4 hours ago
I'm asking because I've been told that COM cannot accelerate when $F_net$ is $0$. I think my question boils down to this : Would an object that is spinning about a non COM axis ever stop ? @AaronStevens
– rsadhvika
4 hours ago
If there are no forces after you release then there is no acceleration.
– Aaron Stevens
4 hours ago
 |Â
show 5 more comments
up vote
1
down vote
favorite
up vote
1
down vote
favorite
Suppose the rod is in space and I apply equal but opposite forces at both ends momentarily. The rod starts spinning around COM and I believe it should keep spinning forever because the COM is not accelerating and angular momentum has to be conserved. No issues in this case.
Next suppose I move the axis of rotation away from the COM, say, to 1/3rd from one end by pinning it,; then apply equal but opposite force at both ends momentarily. What happens now ? Would the rod keep spinning forever ? If yes, wouldn't this mean that the COM is accelerating ? If no, wouldn't this mean that the angular momentum is not conserved ?
angular-momentum
asked 4 hours ago
rsadhvika
28218
Suppose the rod is in space and I apply equal but opposite forces at both ends momentarily. The rod starts spinning around COM and I believe it should keep spinning forever because the COM is not accelerating and angular momentum has to be conserved. No issues in this case.
Next suppose I move the axis of rotation away from the COM, say, to 1/3rd from one end by pinning it,; then apply equal but opposite force at both ends momentarily. What happens now ? Would the rod keep spinning forever ? If yes, wouldn't this mean that the COM is accelerating ? If no, wouldn't this mean that the angular momentum is not conserved ?
angular-momentum
angular-momentum
asked 4 hours ago
rsadhvika
28218
asked 4 hours ago
rsadhvika
28218
edited 4 hours ago
asked 4 hours ago
rsadhvika
28218
asked 4 hours ago
rsadhvika
28218
asked 4 hours ago
rsadhvika
28218
28218
How are you going to move the axis of rotation? That might answer your question. Also, remember Newton's first law.
– Aaron Stevens
4 hours ago
@AaronStevens you've been my life saver today! ty again :) I think I can just nail the rod 1/3rd away from one end and give a little momentary torque so that it starts spinning ?
– rsadhvika
4 hours ago
schoolphysics.co.uk/age11-14/Mechanics/Statics/text/…
– rsadhvika
4 hours ago
I'm asking because I've been told that COM cannot accelerate when $F_net$ is $0$. I think my question boils down to this : Would an object that is spinning about a non COM axis ever stop ? @AaronStevens
– rsadhvika
4 hours ago
If there are no forces after you release then there is no acceleration.
– Aaron Stevens
4 hours ago
 |Â
show 5 more comments
How are you going to move the axis of rotation? That might answer your question. Also, remember Newton's first law.
– Aaron Stevens
4 hours ago
@AaronStevens you've been my life saver today! ty again :) I think I can just nail the rod 1/3rd away from one end and give a little momentary torque so that it starts spinning ?
– rsadhvika
4 hours ago
schoolphysics.co.uk/age11-14/Mechanics/Statics/text/…
– rsadhvika
4 hours ago
I'm asking because I've been told that COM cannot accelerate when $F_net$ is $0$. I think my question boils down to this : Would an object that is spinning about a non COM axis ever stop ? @AaronStevens
– rsadhvika
4 hours ago
If there are no forces after you release then there is no acceleration.
– Aaron Stevens
4 hours ago
How are you going to move the axis of rotation? That might answer your question. Also, remember Newton's first law.
– Aaron Stevens
4 hours ago
How are you going to move the axis of rotation? That might answer your question. Also, remember Newton's first law.
– Aaron Stevens
4 hours ago
@AaronStevens you've been my life saver today! ty again :) I think I can just nail the rod 1/3rd away from one end and give a little momentary torque so that it starts spinning ?
– rsadhvika
4 hours ago
@AaronStevens you've been my life saver today! ty again :) I think I can just nail the rod 1/3rd away from one end and give a little momentary torque so that it starts spinning ?
– rsadhvika
4 hours ago
schoolphysics.co.uk/age11-14/Mechanics/Statics/text/…
– rsadhvika
4 hours ago
schoolphysics.co.uk/age11-14/Mechanics/Statics/text/…
– rsadhvika
4 hours ago
I'm asking because I've been told that COM cannot accelerate when $F_net$ is $0$. I think my question boils down to this : Would an object that is spinning about a non COM axis ever stop ? @AaronStevens
– rsadhvika
4 hours ago
I'm asking because I've been told that COM cannot accelerate when $F_net$ is $0$. I think my question boils down to this : Would an object that is spinning about a non COM axis ever stop ? @AaronStevens
– rsadhvika
4 hours ago
If there are no forces after you release then there is no acceleration.
– Aaron Stevens
4 hours ago
If there are no forces after you release then there is no acceleration.
– Aaron Stevens
4 hours ago
 |Â
show 5 more comments
1 Answer
1
active
oldest
votes
up vote
4
down vote
accepted
To make an object rotate about a point not at the center of mass, you need a joint (hinge) at that location that would supply the necessary forces to accelerate the center of mass (since it is now orbiting a point).
The body is going to move forever because reaction forces do not produce work (they don't add or remove power). The reaction force is either applied through a point that doesn't move (hinge point), or along a direction perpendicular to motion (sliding joint) in general.
Again, the COM does accelerate, but the force needed to do so does not affect the conservation of energy or momentum.
answered 3 hours ago
ja72
19.7k32994
add a comment |Â
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
accepted
To make an object rotate about a point not at the center of mass, you need a joint (hinge) at that location that would supply the necessary forces to accelerate the center of mass (since it is now orbiting a point).
The body is going to move forever because reaction forces do not produce work (they don't add or remove power). The reaction force is either applied through a point that doesn't move (hinge point), or along a direction perpendicular to motion (sliding joint) in general.
Again, the COM does accelerate, but the force needed to do so does not affect the conservation of energy or momentum.
answered 3 hours ago
ja72
19.7k32994
add a comment |Â
up vote
4
down vote
accepted
To make an object rotate about a point not at the center of mass, you need a joint (hinge) at that location that would supply the necessary forces to accelerate the center of mass (since it is now orbiting a point).
The body is going to move forever because reaction forces do not produce work (they don't add or remove power). The reaction force is either applied through a point that doesn't move (hinge point), or along a direction perpendicular to motion (sliding joint) in general.
Again, the COM does accelerate, but the force needed to do so does not affect the conservation of energy or momentum.
answered 3 hours ago
ja72
19.7k32994
add a comment |Â
up vote
4
down vote
accepted
up vote
4
down vote
accepted
To make an object rotate about a point not at the center of mass, you need a joint (hinge) at that location that would supply the necessary forces to accelerate the center of mass (since it is now orbiting a point).
The body is going to move forever because reaction forces do not produce work (they don't add or remove power). The reaction force is either applied through a point that doesn't move (hinge point), or along a direction perpendicular to motion (sliding joint) in general.
Again, the COM does accelerate, but the force needed to do so does not affect the conservation of energy or momentum.
answered 3 hours ago
ja72
19.7k32994
To make an object rotate about a point not at the center of mass, you need a joint (hinge) at that location that would supply the necessary forces to accelerate the center of mass (since it is now orbiting a point).
The body is going to move forever because reaction forces do not produce work (they don't add or remove power). The reaction force is either applied through a point that doesn't move (hinge point), or along a direction perpendicular to motion (sliding joint) in general.
Again, the COM does accelerate, but the force needed to do so does not affect the conservation of energy or momentum.
answered 3 hours ago
ja72
19.7k32994
answered 3 hours ago
ja72
19.7k32994
answered 3 hours ago
ja72
19.7k32994
answered 3 hours ago
ja72
19.7k32994
19.7k32994
add a comment |Â
add a comment |Â
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How are you going to move the axis of rotation? That might answer your question. Also, remember Newton's first law.
– Aaron Stevens
4 hours ago
@AaronStevens you've been my life saver today! ty again :) I think I can just nail the rod 1/3rd away from one end and give a little momentary torque so that it starts spinning ?
– rsadhvika
4 hours ago
schoolphysics.co.uk/age11-14/Mechanics/Statics/text/…
– rsadhvika
4 hours ago
I'm asking because I've been told that COM cannot accelerate when $F_net$ is $0$. I think my question boils down to this : Would an object that is spinning about a non COM axis ever stop ? @AaronStevens
– rsadhvika
4 hours ago
If there are no forces after you release then there is no acceleration.
– Aaron Stevens
4 hours ago