This is the total area of ​​all the surfaces of the figure. The surface area of ​​a cube is equal to the sum of the areas of all its six faces. The surface area is numerical characteristic surfaces. To calculate the surface area of ​​a cube, you need to know a certain formula and the length of one of the sides of the cube. In order for you to quickly calculate the surface area of ​​a cube, you need to remember the formula and the procedure itself. Below we will analyze in detail the order of calculation full area cube surface and give specific examples.

It is carried out according to the formula SA \u003d 6a 2. The cube (regular hexahedron) is one of the 5 types of regular polyhedra, which is regular cuboid, a cube has 6 faces, each of these faces is a square.

For calculating the surface area of ​​a cube You need to write down the formula SA = 6a 2 . Now let's see why this formula has such a form. As we said earlier, a cube has six equal square faces. Based on the fact that the sides of the square are equal, the area of ​​the square is - a 2, where a is the side of the cube. Since a cube has 6 equal square faces, to determine its surface area, you need to multiply the area of ​​one face (square) by six. As a result, we obtain a formula for calculating the surface area (SA) of a cube: SA \u003d 6a 2, where a is the edge of the cube (side of the square).

What is the surface area of ​​a cube.

It is measured in square units, for example, in mm 2, cm 2, m 2 and so on. For further calculations, you will need to measure the edge of the cube. As we know, the edges of a cube are equal, so it will be enough for you to measure only one (any) edge of the cube. You can perform such a measurement using a ruler (or tape measure). Pay attention to the units of measure on the ruler or tape measure and write down the value, denoting it as a.

Example: a = 2 cm.

Square the resulting value. So you are squaring the edge length of the cube. To square a number, multiply it by itself. Our formula will look like this: SA \u003d 6 * a 2

You have calculated the area of ​​one of the faces of a cube.

Example: a = 2 cm

a 2 \u003d 2 x 2 \u003d 4 cm 2

Multiply the resulting value by six. Remember that a cube has 6 equal sides. Having determined the area of ​​one of the faces, multiply the resulting value by 6 so that all the faces of the cube are included in the calculation.

Here we come to the final action on calculating the surface area of ​​a cube.

Example: a 2 \u003d 4 cm 2

SA \u003d 6 x a 2 \u003d 6 x 4 \u003d 24 cm 2

If the side of the cube is a, then
the volume of the cube will be a 3,
area of ​​one side a 2, respectively,
area of ​​six sides (i.e. surface area of ​​a cube) - 6a 2. We believe:

What do we see? As the size of the cube (green line) grows, its surface area (yellow line) gradually increases (from 6 to 216). And the volume of the cube (blue line) is also growing (from 1 to 216). Everyone is growing but the volume grows faster than the surface. You can verify this using the red line, which shows the ratio of surface to volume: per unit volume at the smallest cube account for six units of surface, while the largest has only one.

How can this be assessed? Imagine that each unit of volume is one "man", and the unit of surface is a window through which the man can breathe. Then

• one man lives in a cube with side 1, and he can breathe through 6 windows;

• 8 people live in a cube with a side of 2, and they breathe through 24 windows (each gets 3);

• 27 people live in a cube with a side of 3, and they breathe through 54 windows (each gets 2);

Same for kids who can't calculate the area and surface of a cube

Small children! Take the cube. Do you play dice?

Not! What are we little ones? We play soniplaystation!

Well done children! We took the cubes not to play, but to study biology! Imagine that a man is sitting inside the cube, and the sides of the cube are windows through which he can ventilate the room.

Represented! Cool!

The cube has 6 sides, which means that one little man has 6 windows and he is not stuffy. Now put together two cubes. Now there are 2 little men, and there are 10 windows left, that is, 5 for each.

Oops! Here are those on!

Now make 4 cubes in a square. There are 4 people, 16 windows, 4 for each. And if you put the second floor, i.e. make a super cube 2×2×2, then there will be 8 little men, and 24 windows, 3 for each. Do you feel that it is more and more difficult for little men to air their rooms?

This topic is complex and obscure. Most of my students never really get into it - not by the ninth grade, not by the eleventh - but simply remember the rule: the larger the organism, the smaller its surface area, and vice versa. But it’s better not to cram, but to understand, so I strongly recommend that you take your personal dice (which you still play in secret from everyone) and calculate everything yourself. It's worth it: the rule of the ratio of volume and surface is very often used in our biological economy. Here are a couple of examples for you.

Doctrine of the Megasparrow

Weight birds are volume multiplied by the density, and wing area is the surface. From this it becomes clear that as the size of the bird increases, its mass (cubic function) will grow faster than the size of the wings (quadratic function). Slowly growing wings will find it increasingly difficult to lift the rapidly growing mass.

Practical work: take a sparrow and increase its length by 10 times. In this case, the mass of the bird will increase 1000 times (10 3), and the wing area - only 100 times (10 2). We will get a flightless sparrow, the joy of all predators in the area. To make our mega sparrow fly, we need a second step: increasing the area of ​​\u200b\u200bthe wings another 10 times. A glorious creature will turn out!

Why fat people sweat

The amount of heat generated by the body depends on the number of cells, i.e. from volume. Heat dissipation in environment occurs through the surface of the body. Consequently, with an increase in the size of the body, heat production (cubic function) grows faster than heat transfer (quadratic function). Therefore, it is difficult for large animals to cool down, for them there is a danger of overheating (and vice versa, small animals are always at risk of overcooling).

Elephant with his big size has, quite clearly, a very large surface area. But in relation to volume its surface is very small. In order to get rid of excess heat, the elephant uses huge ears. They are needed not at all for good hearing (for example, predators have good hearing - their ears are small), but to increase the surface of the body through which heat transfer occurs.

At this place, the children ask: "- in India and Africa - is it really so hot there?". Answer: unfortunately, in our cool latitudes, the elephant could not find enough food for himself (and where would he hide during the winter?) Mammoths (relatives of the elephant, living in slightly cooler conditions), saved heat: they had normal size ears and fur as it should be for mammals).

The wife, while drawing this drawing, complained several times that the elephant is a typical alien, just look at him! Indeed, for Russians, an elephant is a completely ordinary animal, even a native one, but this is solely due to the talent of Korney Ivanovich Chukovsky: “And the Elephant-dandy, a hundred-pound merchant’s wife, and the Giraffe is an important count, as tall as a telegraph.” (Chukovsky K.I. “Crocodile”) Residents of other countries, deprived of Chukovsky, perceive the elephant in a completely different way: “Its knives were like trees, its ears flapped like sails, its long trunk was raised, like a formidable snake ready to pounce, small eyes inflamed." (Scrombie S. "Delivery of valuable goods: expert advice")

If you are interested in the question of what shape of the body - its total surface area is the smallest, then you need to keep in mind that the volumes of the compared bodies must, of course, be the same.

What is needed for the experiment?

To conduct such a research experiment, you will have to apply, in addition to small, simple sculpture lessons, quite accessible to each of you, the knowledge of stereometry. We hope that this informative study will be useful and exciting for you.

Take a small piece of plasticine, or, if it is not available, a piece of well-kneaded clay. Sculpt a cube. Try to make it with equal sides and right angles. Measure the length of its edge and write it down.

Then, from the same cube, fashion a cylinder. The ratio of the dimensions of the bases and the height does not matter. It is important that this is the correct cylinder. Measure the radius of its base and height, and write it down too.

Shape the cylinder into a ball. With some effort, you can achieve that you get a real ball. Measure its radius (this is easy to do by piercing it with a needle or a straight, stiff wire through its center). After you write down the radius of the ball, if you wish, fashion other geometric bodies from the ball, for example, a cone, a pyramid, and so on.

Experiment results

And so, you wrote down the sizes of different geometric bodies. Their form is the most diverse, but they have one thing in common - they all have the same volumes. After all, they are all molded from one piece of clay or plasticine.

With the accepted volume of plasticine or clay, for example, one cubic centimeter - you should get, after appropriate measurements, the following approximate data on the total surface area for various figures: a ball - 4 centimeters square; cube - 6 centimeters square; cone - 7 centimeters square; cylinder - 8 centimeters square.

The laws of physics

When you blow a soap bubble, it has the shape of a ball.

Have you observed dew drops on the leaves of plants in summer? There are droplets so small that they do not flatten under their own weight. They look like balls.

Water and other liquids have on their surface the thinnest, invisible to the eye, molecular film. It is resilient in water. This elastic film is always trying to shrink, that is, to take up less space, while forming the smallest possible surface. And you have already seen that the smallest surface area of ​​the ball.

Astronauts who are in a state of weightlessness can observe how even such a portion of water that can fit in a glass melts in the air in the form of a ball. On Earth, under the influence of gravity, water spreads and, in order to preserve it, it is poured into vessels.

But on the surface of an overflowing glass, a bulge formed by water is clearly visible. An invisible molecular film tends to keep water from overflowing. The water film is quite strong. A needle carefully placed on the surface of the water will lie on it, slightly pressed, forming a small depression.

The ratio of volume to surface area of ​​any physical body. One of the most important engineering techniques.

Imagine a cube with an edge length of 1 meter (1 centimeter, 1 foot, 1 inch or 1 "whatever you want"), then there will be a meter - for simplicity. The volume of this cube is 1 m 3. Each side has an area of ​​1 m 2, and the entire surface area of ​​​​this cube is 6 m 2 - there are six sides. The ratio of volume to surface area is 1:6 \u003d 1/6 (now and further - without taking into account the dimension).

Now imagine a cube with a side of 3 m. The volume of this cube is 27 m 3 (3x3x3). Each side has an area of ​​9 m 2 , and the total surface area of ​​this cube is 54 m 2 . The ratio of volume to surface area is 27:54 = 1/2 = 3/6.

That is, with an increase in the linear size by 3 times, the surface area increased by 9 times, but the volume increased by 27 times. The ratio of volume to surface area increased by 3 times.

The table below shows the calculations for cubes when doubling the linear size step by step:

Table. Comparison of the dynamics of the surface area and volume of a physical body with the growth of the linear size.

With the growth of the linear size, the volume increases much faster than the surface area of ​​the body, since the volume is proportional to the cube of the linear size, and the area is proportional to the square. This fact applies not only to cubic bodies, but also to any other bodies, of course, while maintaining the shape (or proportions, if you prefer).

Picture. Comparison of the dynamics of the surface area and volume of a physical body with the growth of the linear size.

1) Heat transfer is proportional to the surface area. Heat capacity - the volume of the body. It directly follows from this fact that a larger building (of the same shape) will give off the heat accumulated during daylight hours (or heat up during the day) for a longer time and will require less energy per unit of usable area -! usable area is directly proportional to the internal volume! - for heating (air conditioning).

2) Mass (weight) is proportional to the support volume. Ground load - surface area. From this fact it directly follows that for a support of any shape there is a size, starting from which (while maintaining the shape) it will go into any soil.

3) A child has a completely different area/volume ratio than an adult. Therefore, the risks of hypothermia or heat stroke for a child are disproportionately higher (which, of course, is partly offset by a different rate of metabolic processes in children).