PHYSICS QUESTION! How do I find center of mass?

[GRagland]

I know how to find the center of mass of obects on a 1 demensional plane [CenterOfMass=(M1X1+M2X2)/(M1+M2)].
But how do i do it for objects spread out on a 2d plane?

 

[beer]

What level math are you in?

Some of the methods involve integrating over the entire surface of the object, I believe.

 

[beer]

General Center of Mass Discussion: http://hyperphysics.phy-astr.gsu.edu/hbase/cm.html
For a solid body: http://hyperphysics.phy-astr.gsu.edu/hbase/cm.html#cmc

 

[GRagland]

I dont understand those links you provided me... I'm taking phys 101.

 

[beer]

OK, once again I repeat.

What level math is required for your physics course?

 

[dighn]

you should be able to limit it to one dimention at a time eg first for all the x components, then for all the y components

 

[GRagland]

Originally posted by: Elemental007
OK, once again I repeat.

What level math is required for your physics course?

Precalculus. Its not calculus based physics.

 

[Heisenberg]

Are you talking about a continuous distribution of mass or point masses? If you're talking about point masses, just find the distance from each axis and use the center of mass formula as usual.

Edit: Typed before engaging brain

 

[beer]

I wish I could help ya, but I only have my E&M book here, and my mechanics book is at my apt, and I'm at my girlfriends. The only equation I have for CoM is what's on our equation sheets, https://hw.utexas.edu/bur/Formulae_Mech_page1.pdf, which is of absolutely no use to you unfortunately

 

[GRagland]

http://www.hapman.com/images/1%20bulk%20bag%20unloader%20crate%20.jpg

Look at that pic, now imagine its a bunch of wood boxes stacked up and some of the boxes were missing in places (so the cm is not in the very middle. Where underneath it would it balance on a pole?.... this is prolly the worst example i could possible make, but hopefully someone understands. I need the formula to solve problems like this.

 

[ThunderbirdElitist]

I know some that are simple but require double integrals so I doubt it will do you any good being in pre-calc

 

[GRagland]

Guys this is much simpler then you think.... i know you guys can help me.


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Above is a diagram of some boxes, the number is the mass of each box. There is no space between the boxes. What is the x/y coordinates of the CM if the bottom right corner is the origin and each box is one unit.

 

[Heisenberg]

If each box is a point mass, then just use the center of mass equation for each direction (i.e x and y).

 

[silverpig]

Originally posted by: Heisenberg
If each box is a point mass, then just use the center of mass equation for each direction (i.e x and y).

 

[GRagland]

Ok, i got (x, y) = (13/10 units, 21/10 units) if the bottom right corner is the origin. Is this right?

 

[TuxDave]

Originally posted by: GRagland
Guys this is much simpler then you think.... i know you guys can help me.


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Above is a diagram of some boxes, the number is the mass of each box. There is no space between the boxes. What is the x/y coordinates of the CM if the bottom right corner is the origin and each box is one unit.

If bottom right is origin, center of mass is at x=-1.8, , y=+2.1

 

[TuxDave]

Dammit 2x post, I guess I'll use the derivation here.

X coordinate calculation

X = 1/10*(2*-0.5+3*-1.5+5*-2.5)
Y = 1/10*(1*0.5+2*1.5+7*2.5)