First, Newton's first law of inertia:
When everything is around, it always stays in a state or. This is Newton's first law, also known as
Law. We call an object the property of maintaining inertia. The concept of inertia can be used to explain the related inertial phenomena. )
Second, the combined force:
1. If one force produces the same effect as several forces * * *, this force belongs to those forces.
2. Two forces are on the same line, and the resultant force in the same direction is equal to the magnitude, direction and direction of the resultant force.
3. The resultant force of two forces in opposite directions on the same straight line is equal to the magnitude of these two forces, and the direction of the resultant force is the same as that of the other force.
Third, the balance between the two forces:
When an object is subjected to several forces, if it maintains a state or, we say these forces. If the two forces acting on an object are magnitude and direction, and the two forces are balanced with each other (the resultant force is zero).
Fourth, quality and density.
(1) is called quality. Any object has mass, and its mass does not change with the change of temperature. The unit of mass is (kilograms), and the commonly used units are tons (tons), grams (grams) and milligrams. It is often used to measure the mass of objects in experiments.
(2) How to use the balance of the tray:
1, put the balance on the table before use, and put the stray code on the left end of the scale.
2. Adjust the balance nut of the beam again, so that the pointer points to the position of the indexing plate, and then the beam is balanced.
3. When in use, put the measured object on the flat plate and the weights on the flat plate, add and subtract the weights on the right flat plate with tweezers and adjust the position on the scale until the balance beam is balanced again, and the mass of the object is equal to the sum of all the weights on the right flat plate. (When the position of the object and weight is reversed, subtraction is used.)
(3) A substance called this substance. Density is a substance. Density, mass and volume are usually expressed by letters, and the formula for calculating density can be written as follows:
(4) If the mass unit is kg and unit of volume is m3, the density unit is:
(5) The density of pure water is kg/m3= g/cm3, and that of mercury is.
1 m3 = dm3 (l) = cm3 (ml) = mm3.
(6) To measure the density of an object, we should first measure the sum of the measured objects, and then calculate the density value with the density formula. Volumes of liquids and irregular solids can be used.
Application of density: (1) Find the density by formula and identify substances; (2) Find the quality by formula. (3) Calculate the volume with the formula.
Six, buoyancy
The drag of (1) fluid on an object immersed in it is called buoyancy in physics.
(2) The formula for finding buoyancy by weighing method is:
(3) The formula for finding buoyancy by cause method is:
Seven, Archimedes principle
1. An object immersed in a liquid is subjected to vertical buoyancy, and the buoyancy is equal to that of the liquid it displaces. The formula is, the variant forms are and. This principle also applies to gases.
2. Buoyancy is related to the sum of displaced liquids, but the buoyancy of submerged objects has nothing to do with it.
Eight, the ups and downs of the object conditions:
(1) The ups and downs of an object depend on what it receives.
There are big ones and small ones.
1. When the object is immersed in liquid: ① When F floats < G, the object; (2) when f floats > g, the object; (3) When F float = G object, object or.
2. The difference between floating and floating: (the difference between V lines and V objects)
3. Application of ups and downs: density meter (the density of liquid is in direct proportion to V-shape), salt water seed selection, submarine (floating), ship (floating forever, F =G, floating when sailing from the river into the sea), balloon, airship (floating).
(2) The ups and downs of a solid object can also be judged by its size and the size of liquid. (1) When the object floats; (2) When the object sinks; (3) When the object is suspended.
(3) The formula for finding buoyancy by balance method is:
Nine, pressure
1, the force acting vertically on the stressed surface of an object is called. The direction of pressure is on the stress surface and point. The role of stress is determined by * * *.
(Note: Pressure is not gravity. For a horizontally placed object, pressure equals gravity. )
2. The object is called pressure, which is represented by symbols. Pressure is a physical quantity described. The definition of pressure is:, and the unit of pressure is:, which is expressed by symbols.
3, increase or decrease the pressure:
From the formula P=F/S, it can be known that when the stress area is fixed, the pressure can increase with the increase; When the pressure is constant, the increase can be reduced.
Liquid pressure transmitter
1, the pressure of the liquid is caused by the fact that due to the fluidity of the liquid, the liquid exerts pressure on both the side wall and the bottom of the container. Liquid has pressure in all directions. The pressure inside the liquid increases with the increase. At the same depth, the pressure of liquid in all directions. The pressure of the liquid is also the same as.
2. The formula for calculating liquid pressure is: According to the formula, the pressure of liquid is only related to sum; The pressure of the liquid has nothing to do with the gravity, mass and volume of the liquid and the shape and size of the container.
3. The upper and lower containers are called connectors.
4. Features of the communication device: When the same liquid exists in the communication device, the liquid level in each container always remains the same (principle: the pressures generated on both sides are equal).
Xi。 atmospheric pressure
1, the pressure produced by the atmosphere on the object immersed in it is called, or abbreviated as. (The reason is that the atmosphere is also influenced by gravity and has fluidity. )
2. Famous experiments in history proved the existence of atmospheric pressure. This experiment accurately measured the atmospheric pressure for the first time. In this experiment, when the mercury column in the tube drops to a certain height, the mercury column inside and outside the tube is affected by atmospheric pressure, which supports the mercury column inside the tube. The pressure produced by the mercury column at this height is the same as the atmospheric pressure. Usually, the pressure of Pa is called standard atmospheric pressure, which is equivalent to the pressure generated by a mercury column with a meter height. Atmospheric pressure can be measured.
3. Atmospheric pressure value increases with height. The boiling point of all liquids is when the air pressure decreases; When the air pressure increases.
When the temperature is constant, the smaller the volume of a certain mass of gas, the smaller the pressure; The bigger the volume, the greater the pressure.
Twelve. Velocity and pressure of fluid
The higher the velocity of the fluid, the greater the pressure. (This phenomenon will be explained)
Thirteen, simple machinery (lever, pulley and pulley block)
1, under the action of force, a hard rod (bendable) that can rotate around it is called a lever, and this fixed point is called. The force acting as a lever is called power, the force acting as a lever is called resistance, the distance between fulcrum and power action line is called, and the distance between fulcrum and resistance action line is called.
2. The equilibrium condition of the lever is:, which can be expressed as. The power arm L 1 is n times that of the resistor arm L2, and the power arm F 1 is twice that of the resistor F2.
3, three kinds of levers: (1) labor-saving lever: power arm resistance arm, power resistance; This kind of leverage saves money and costs. (2) laborious lever: power arm resistance arm, power arm resistance; This kind of leverage is wasted and saved. (3) Equal arm lever: power arm resistance arm, power resistance; This lever is neither. (Balance and crown block are a kind of lever)
4. Principle of odd motion and even determination: When using the pulley block, the number of rope segments directly bearing heavy objects is n ... If n is even, the fixed end of the rope is hung on the pulley; If n is odd, the fixed end of the rope is hung on the pulley.
5. The crown block is essentially a lever; It is not economical to use crown block, but it can be changed.
6. The moving pulley is actually a lever with a force arm equal to twice the resistance arm; Using movable pulley can save, but it can't be changed.
7. The pulley block can be used or replaced; When using the pulley block, the pulley block uses several ropes to lift the object, and the force used to lift the object is the weight of the object, that is, F=(G object +G motion) /n. S=nh. (When placed horizontally, F=f/n, S=nS/).
Fourteen Work and energy
1, a force acts on an object and makes it pass through a section on the ground. This force does work on the object. The work mentioned in mechanics contains two necessary factors: one is; The second is. Calculation formula of work: where f represents the force acting on the object, s represents the distance the object passes in the direction of the force, and w represents the work done by the force on the object. The international unit of work is, represented by symbols.
2, the use of any machinery can not be saved, this conclusion is called. 1, kinetic energy is the energy that an object has because of it, and its calculation formula is, indicating the magnitude of kinetic energy and the object's
And related.
3. Gravitational potential energy is the energy that an object has because of it. Its formula is that the magnitude of gravitational potential energy is related to the sum of objects.
4. Elastic potential energy is the energy that an object has because of it. Its formula is that the magnitude of kinetic energy is related to the sum of objects.
5. Mechanical energy is the sum total. The mathematical expression is.
6. Internal energy is the sum of all molecules in an object, and its size is related to the object. There are two ways to change the internal energy of an object: and.
7. Heat refers to how much heat is absorbed or released during heat transfer. His formula is, or it can be written as or.
Fifteen, mechanical efficiency
1, useful work is useful to people (usually w is useful =Gh), and redundant work is useless to people, but it has to be done.
The work done by power is called total work: total work = useful work+extra work. That is, wtotal = useful+whextra (usually W total =FS).
2. Mechanical efficiency is the ratio of and is expressed in letters. The formula of mechanical efficiency is: (the efficiency of any machine is less than 1)
3. The mechanical efficiency formula of pulley block can also be written as follows
Or ... It's just about and.
Sixteen. force
1, what is done in unit time is called power, which is expressed by symbols, and power is a physical quantity representing an object;
2. The formula for calculating power is:, the international unit of power is, expressed by symbols.