At a number of mathematical and physical calculations, there is a need to find out - the ruler is a material point? Everything depends on statements of the problem. Let's remember that the material point, is the insignificant size which when calculating can be neglected.
As a rule, such tasks occur in the school program, but also in life, we quite often operate with various sizes, respectively it is always necessary to know whether it is possible to neglect one of sizes or not.
The wrong definition of a material point, will lead to a global mistake in calculations with its participation. Relatively to a ruler, it is possible to be guided by the following comparative principle – ruler size to the size of the space measured with its help is how significant.
For example, if to measure by a ruler room perimeter, then its size will have a certain value, that is it is not considered a material point in this situation. And if to use a ruler for measurement of the terrestrial equator or space distances, then in relation to these calculations, the ruler, certainly, will be a material point. That is the size which can be neglected, without loss of accuracy of calculations.
Definition of a material point depending on the nature of the movement
One more factor influencing definition of a material point is the character and the direction of the movement. If the ruler progressively moves (on the straight line which is strictly combined with a moving body, and at the same time being parallel in relation to itself), then in independence of distance of the observer the ruler is considered a material point.
As an example, it is possible to present splitting of a ruler on a set of particles, all of them will equally move in one direction parallel to a straight line with one speed and on identical removal from each other.
At commission of any movement, but at the remote distance from the observer, one may say, not the movement of separate parts, but its movement as uniform object will be important. Then the ruler is considered a material point. But, at commission by a line of any movements at distance comparable to its sizes, the ruler cannot be considered as a material point.
Geometry of a material point
When calculating, it is always necessary to remember that the material point has no own geometry. So, the planet Venus can be considered a material point if the distance to the planet Earth, or address speed around the Sun is calculated it.
But when determining volume or length of the equator of the planet, the planet cannot be a material point.
This definition generally depends not on a type of the made movement by an object, and on the size of movement along the instrument of measurement or the object, in our case it is a ruler.
At rotary motion, the ruler will never be considered as a material point, at forward, depending on other applied sizes.