# Point-like body

1. Aug 5, 2005

### MathematicalPhysicist

my question is as follows:
when do we need to consider a three dimension body as a point like body in our calclulations?
i mean outside our theoretical/homework practices when should we assume the body as a point like?

one thing i can think of is when the geometric properties of a body is not important and therefore isnt taken into consideration into our calculations.
and maybe also when the body is a particle but other than that i dont know.

2. Aug 5, 2005

### Antiphon

When it makes it easier or possible to solve the problem.

3. Aug 5, 2005

### pervect

Staff Emeritus
We can treat the Newtonian gravitational field (GM/r^2) of a spherically symmetric body as if the body were a point.

The center of mass is a useful concept for the motion of rigid bodies as well. If we apply a force to a rigid body, we know that the acceleration of the center of mass is F/m.

4. Aug 6, 2005

### Danger

I don't do much in the way of science other than haunting these premises. My experience with your question actually is the basis of how I play and teach pool. When calculating how to hit a ball, I treat each one as a mathematical point rather than a spherical object. I then envision what angle to fire a laser at in order to achieve the proper 'reflection', followed by extrapolating the radii in order to accommodate the edge-to-edge contact of the balls.

5. Aug 6, 2005

### MathematicalPhysicist

and ofcourse you always lose... :rofl:

6. Aug 6, 2005

### Danger

Oooh... you sting me! (Wanna play for \$? :tongue: )