http://dev.physicslab.org/Document.aspx?doctype=3&filename=RotaryMotion_CenterMass.xml
This is the site can anyone tells me why this works?i mean it states this
1.Another method of finding the center of mass of an planar object is through the use of a plumb line. Suspend the mass from each vertex and trace the plumb line's location.
2.Since the center of mass will fall below the suspension point (in order to reduce any torques from the object's weight) the center of mass will be at the intersection of all of the plumb lines.
Why would center of mass fallbelow the suspension point. bear in mind i dont actually have a clue what is meant in the brackets? help?
This is the site can anyone tells me why this works?i mean it states this
1.Another method of finding the center of mass of an planar object is through the use of a plumb line. Suspend the mass from each vertex and trace the plumb line's location.
2.Since the center of mass will fall below the suspension point (in order to reduce any torques from the object's weight) the center of mass will be at the intersection of all of the plumb lines.
Why would center of mass fallbelow the suspension point. bear in mind i dont actually have a clue what is meant in the brackets? help?
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How convenient, I just answered this question for someone else so all I have to do is copy and paste. Note that in my explanation the "non-vertical component of force" from the string tension that I refer to would be a torque acting on the object.
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The nifty property of the center of gravity is that we can treat the entire object as if it were just one point. So for any object suspended by a string there will be two forces acting on it:
1) The downward force of gravity
2) The tension in the string
Now the object will only reach an equilibrium position (that is, a position at rest) when gravity and tension act in opposite directions. This only occurs if the center of gravity lies directly underneath the string. Note that if the CG doesn't lie directly underneath the suspension point you have a non-vertical component of force from the string tension so the object will not be at rest.
So you can draw a line from the suspension point to the bottom of the object and know that the CG must lie somewhere on that line (your teacher probably referred to this line as an "axis"). By choosing another suspension point that doesn't lie on the line we've drawn we'll find a different line on which the CG must lie. The point at which the two lines intersect will be the CG (two non-parallel lines can only intersect at one point).
Note that the way the force from the tension in the string is transmitted to the center of gravity is via intermolecular forces. This isn't important to the visualization but figured I'd mention it in case you were wondering about how the CG has tension exerted on it.
As for the question about the heavier body hanging below the head it just depends on where the suspension point is. If the point were on the body of the duck instead of the head then the head would lie below the body.
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The nifty property of the center of gravity is that we can treat the entire object as if it were just one point. So for any object suspended by a string there will be two forces acting on it:
1) The downward force of gravity
2) The tension in the string
Now the object will only reach an equilibrium position (that is, a position at rest) when gravity and tension act in opposite directions. This only occurs if the center of gravity lies directly underneath the string. Note that if the CG doesn't lie directly underneath the suspension point you have a non-vertical component of force from the string tension so the object will not be at rest.
So you can draw a line from the suspension point to the bottom of the object and know that the CG must lie somewhere on that line (your teacher probably referred to this line as an "axis"). By choosing another suspension point that doesn't lie on the line we've drawn we'll find a different line on which the CG must lie. The point at which the two lines intersect will be the CG (two non-parallel lines can only intersect at one point).
Note that the way the force from the tension in the string is transmitted to the center of gravity is via intermolecular forces. This isn't important to the visualization but figured I'd mention it in case you were wondering about how the CG has tension exerted on it.
As for the question about the heavier body hanging below the head it just depends on where the suspension point is. If the point were on the body of the duck instead of the head then the head would lie below the body.