Palmistry 

Determination of the center of gravity of a flat figure laboratory work. The positions of the center of gravity of some figures

If a flat plate is suspended at any point, then it will be located in such a way that a vertical line drawn through the suspension point passes through the center of gravity of the plate. This allows you to find the center of gravity of flat plates empirically. To do this, after hanging the plate at some point, draw a vertical line on it passing through the point of suspension. Then do the same operations again, hanging the plate at its other point. The point of intersection of the drawn lines will give the position of the center of gravity of the plate.
To verify this, the plate can be hung at a third point. The vertical line passing through the suspension point must pass through the intersection point of the first two lines.
You can also balance the plate on the tip of a pin. The plate will be in equilibrium if the fulcrum coincides with the center of gravity.
Devices and materials: 1) a ruler, 2) a flat plate of arbitrary shape, 3) a plumb line,
4) a pin, 5) a tripod with a foot and a clutch, 6) a cork.

Work order
1. Clamp the stopper into the tripod foot in a horizontal position.
2. Using a pin that sticks into the cork, hang the plate and the plumb line.
3. With a sharpened pencil, mark the plumb line on the lower and upper edges of the plate.
4. Having removed the plate, draw a line on it connecting the marked points.
5. Repeat the experiment by hanging the plate at a different point.
6. Make sure that the point of intersection of the drawn lines is the center of gravity of the plate.

Test. Body weight. Relationship between body mass and gravity.


1. What force is called weight?

a) the force with which the Earth attracts bodies to itself;

b) the force arising from the deformation of tension or compression;

c) the force with which the body, due to attraction to the Earth, acts on the support or suspension.



3 . How is body weight directed?

a) vertically down;

b) vertically up;

c) to the right.


4. Body weight is indicated

a) m;

c) F heavy


5. What is the approximate mass of a body weighing 120N?

b) ≈ 12 kg;


Lesson topic: “Conditions for the equilibrium of bodies. Center of gravity of the body.


"The center of gravity of each body is some point located inside it - such that if you mentally hang the body behind it, then it remains at rest and retains its original position." Archimedes


The center of gravity of the body.

  • The center of gravity of a body is the point through which the resultant of all gravity forces acting on individual elements of the body passes.
  • Find the centroid of these figures.
  • Find the centroid of these figures.
  • Find the centroid of these figures.
  • Find the centroid of these figures.


TYPES OF EQUILIBRIUM

indifferent

sustainable

unstable



Interestingly, when a person is sitting, he is in a more stable position than when he is standing. A seated person has a lower center of gravity than a standing person. A more stable position is considered when the center of gravity of the body is located as low as possible.

Center of gravity

So when descending a mountain, an experienced skier crouches slightly. At the same time, its center of gravity drops, and the skier is in a more stable position.






Dependence of stability on the area of ​​support

1. Stable is the body whose area of ​​support is larger.



Laboratory work.

Determination of the center of gravity flat plate.


Objective:

learn to determine the center of gravity of a flat plate.


Devices and materials:

Ruler, flat plate of arbitrary shape, plumb line, pin, tripod with foot and clutch, cork.







Homework

1. Find the centers of gravity geometric shapes: square, triangle, circle.




The course of work Any real body with finite dimensions and mass can be considered as a set of its constituent parts. Each of these parts is individually affected by the force of gravity. The force of gravity, which acts on the body as a whole, is the resultant of these forces. The point of application of this resultant is usually called the center of gravity of the body.


Task 1: Determine the position of the center of gravity of a flat figure of arbitrary shape Using scissors, cut out a figure of arbitrary shape from cardboard. Attach the thread to it with adhesive tape at point A. Hang the figure by the thread to the foot of the tripod. Using a ruler and a pencil, mark the vertical line AB on the cardboard.






Task 2: Using only a ruler and a pencil, find the position of the center of gravity of a flat figure. Using a pencil and a ruler, divide the figure into two rectangles. By construction, find the positions O 1 and O 2 of their centers of gravity. Obviously, the center of gravity of the entire figure is on the line O 1 O 2


Task 2: Using only a ruler and a pencil, find the position of the center of gravity of a flat figure. Divide the figure into two rectangles in a different way. By building, find the positions of the centers of gravity O 3 and O 4 of each of them. Connect the points O 3 and O 4 with a line. The point of intersection of the lines O 1 O 2 and O 3 O 4 determines the position of the center of gravity of the figure


Task 3: Determine the position of the center of gravity of the triangle. Using tape, secure one end of the thread to the top of the triangle and hang it from the foot of the tripod. Using a ruler, mark the direction AB of the line of action of gravity (make a mark on the opposite side of the triangle)


Task 3: Determine the position of the center of gravity of the triangle. Repeat the same procedure, hanging the triangle at vertex C. On the opposite vertex C of the side of the triangle, make a mark D. Using adhesive tape, attach pieces of AB and CD threads to the triangle. The point O of their intersection determines the position of the center of gravity of the triangle. AT this case the center of gravity of the figure is outside the body itself.



This work is intended for the practical part of physics: Center of gravity. The difficulty is that there is no job description in the textbook. It is convenient to print practical work for each student, and pre-set homework on preparing models (this saves time in the lesson).

Goals. The tasks are defined in the presentation on this topic.

Here is a rough plan for 7th grade students.

Practical work "Determination of the center of gravity of a flat plate"

Target : Finding the center of gravity of a flat plate.

Devices and materials : a flat plate of arbitrary shape, cut out of paper, a thread with a load, a needle, a pencil, a ruler.

Working process

    Thread the needle. Attach a weight (such as an eraser) to one end of the thread.

    Insert the needle into the plate near the edge so that the plate rotates freely on the needle (Fig. 1). The thread should hang freely along the plate

    Mark with a pencil 2 points on the upper and lower edges of the plate through which the thread passes (indicate with points A and B)

    Use a ruler to draw a line through these points.

    Repeat the experiment 2 more times, hanging the plate at other points.

    The lines should intersect at one point - the center of gravity of the plate. Mark it on the plate ( point O).

Any real body with finite dimensions and mass can be considered as a set of its constituent parts. Each of these parts is individually affected by the force of gravity. The force of gravity, which acts on the body as a whole, is the resultant of these forces. The point of application of this resultant is called center of gravity of the body