How to calculate the support

1. The density of mercury is 13.6g/cm ^ 3, and the density of iron block is 7.9g/cm ^ 3. If the quantity of mercury is enough, the iron block will have v row = 13.6 / 7.9 * V immersed in mercury, but in fact, the depth of mercury is only 3cm, so the iron block still has a certain pressure on the bottom of the container.
the actual size of floating force on the iron block is: F floating = density of mercury * g * (3cm * 8cm * 8cm) = 26n

2. The weight only increases the gravitational potential energy, as long as the height change is calculated
two right triangles can be made from two positions AB, and the bottom length of the two triangles can be expressed by height H. the difference between them is 2, and the height h can be solved. Then the oblique side length of the two triangles can be calculated respectively, and the difference is the change of height.

3. The supporting force in junior high school physics, according to the motion state of the object, is calculated indirectly after the force analysis and according to the balance of the two forces
△ the supporting force in high school physics, according to the motion state of objects, after force analysis of multiple objects, one is: according to the balance of two forces, the supporting force is indirectly calculated; Second, according to Niu Er's law, support force can be calculated indirectly

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4. What, the pressure is equal to the support force
only when the object is in equilibrium on the horizontal plane, the pressure is equal to the gravity. At this time, the pressure = the support force = the gravity

5. Normally, the supporting force is on the contact surface, but for convenience, it is drawn on the same point of action with gravity, that is, the geometric center. You can see the supporting force in the geometric center in your exercise book

6. gravity

7. What you understand is right

8. (1) Determine the position of the fulcrum of the lever
(2) distinguish the power and resistance of the lever, make clear its size and direction, and make a schematic diagram of the output as much as possible
(3) determine the arm of each force
(4) according to the lever balance condition, the relationship is listed and analyzed
(1) according to the actual situation of people doing push ups, the relationship between the power arm and the resistance arm is analyzed, and the type of lever is judged. (2) using the condition of lever balance, the support force can be calculated, and the work can be calculated according to w = FS; With o as the fulcrum, the distance ob from O to the human gravity line is the resistance arm, and the distance OA from O to the arm's supporting force line is the power arm. It can be seen from the figure that the resistance arm is smaller than the power arm, so it is a labor-saving lever

9. It depends on the specific situation. If it is in equilibrium, it is the same as the force in the same direction as the supporting force. If it is in non-equilibrium, it is not easy to say. For example, when the supporting force of circular motion provides centripetal force, it is required to be greater than gravity. There are still many cases, so it can't be generalized.

10. When there is only gravity and supporting force in the up and down direction:
things fall down: Gravity & gt; Supporting force
standing in the east-west direction: gravity = supporting force