What are the physics knowledge points in the first year of junior high school? Sorting out the physi

The phenomenon of light, the movement of objects, and the sound.

Reading. Or ask the teacher. Useless.

1. Density is not necessarily constant. Density is a property of matter, which has nothing to do with mass volume, but is related to temperature, especially the density of gas changes significantly with temperature.

2. When the balance is read, the code should look at the left side, and the mobile code is equivalent to adding or subtracting weights in the right plate of the balance.

3. The speed of uniform linear motion must be unchanged. As long as it is a linear motion at a uniform velocity, the velocity must be a fixed value.

4. The average speed can only be the total distance divided by the total time. Finding the average speed on a certain stretch of road is not the average of the speed, but the total distance divided by all the time spent on that stretch, including the time spent in between.

5. The size of inertia has nothing to do with speed. The magnitude of inertia is only related to mass. The greater the velocity, the more kinetic energy the object can do, not the greater the inertia.

6. The difference between the equilibrium force and the interaction force: The equilibrium force acts on one object, and the interaction force acts on two objects.

7. The change of the motion state of the object must be subjected to force, and the force does not necessarily change the motion state. Force is what changes the state of motion of an object. The force is also included in the equilibrium force, and the state of motion remains unchanged.

8. Inertia is a property and not a force. It cannot be said that it is received, it can only be said that the object has inertia.

9. The steps of force analysis: determine the research object; Find gravity; Find contact objects; Determine whether there are other forces such as pressure, support, friction, and tension between the object in contact.

10. The equilibrium force of the object and the equilibrium state of the object (stationary or uniform linear motion) can be inferred from each other. When an object is subjected to an unbalanced force, if the unbalanced force and the direction of motion are the same, the object will accelerate its motion, and vice versa, it will decelerate.

11，1kg≠。Two different physical quantities can only be transformed with formulas.

12. Spring dynamometer and balance can be used on the moon, and the balance cannot be used in the state of weightlessness in space, and the spring dynamometer can also measure other forces other than gravity, such as tensile force.

13. The friction does not necessarily increase when the pressure increases. Sliding friction is related to pressure, but static friction is not related to pressure, but only to the force that balances it.

14. The contact of two objects does not necessarily have the action of force. It also depends on whether there are conditions such as extrusion, relative motion, etc.

15. The friction force is related to the roughness of the contact surface, and the pressure is related to the size of the contact area.

16. Lever leveling: left high and left tone; Balance leveling: The hands are biased to the left and right. The balance nuts on both sides are adjusted in the same direction.

17. The movable pulley does not necessarily save half the effort. When lifting heavy objects, only by pulling vertically can you save half of the effort.

18. The power is the smallest, and the force arm should be the largest. Arm maximum: Find a point on the lever so that the distance from this point to the fulcrum is the farthest.

Junior high school physics formulas are envious.

1. The velocity formula of uniform linear motion:

Find velocity: v=s t

Find the distance: s=vt

2. The speed formula of variable speed linear motion: v=s t

3. The relationship between the weight and mass of an object: g=mg

g = 4, the definition of density.

Find the density of a substance: =m v

Find the mass of the substance: m = v

Find the volume of the substance: v=m

4. Calculation of pressure.

Definition: p=f s (the substance can be applied in any state) liquid pressure: p= gh (h is the depth).

Find the pressure: f=ps

Find the force area: s=f p

5. Calculation of buoyancy.

Weighing method: f float = g—f

Formula method: f float = g row = v row g

Floatation method: F float = g object (v row v object).

Suspension method: silver F float = g object (V row = V object brother line).

6. Leverage balance condition: f1l1=f2l2

7. Definition of work: w=fs

8. Power definition: p=w t

For the case of uniform linear motion: p=fv

f is power) 9, mechanical efficiency: =w useful w total.

For lifting objects:

w useful = gh (h is the height).

W total = FS10, bevel formula: FL = gh

11. Endothermic and exothermic conditions when the temperature of the object changes.

Q aspiration = cmδt

t=t-t0）

Q amp = cmδt

t=t0-t）

12. Calculation of the heat emitted by fuel combustion: q discharge = qm

13. Thermal equilibrium equation: q suction = q discharge.

14. Heat engine efficiency: =w useful

q put. q-amp=qm).

15. Current definition: i=q t

q is the amount of electricity, and the unit is coulombs.

16. Ohm's law: i = u r

Deformation voltage: U=IR

Deformation resistance: r=u i

17. The characteristics of the series circuit: (taking the series connection of two pure resistive electrical appliances as an example) the relationship between voltage: U=U1+U2

Relationship of current: i=i1=i2

Relation of resistance: r=r1+r2

18. Characteristics of parallel circuits: (taking the parallel connection of two pure resistive electrical appliances as an example) the relationship between voltage: u=u1=u2

Relationship of current: i=i1=i2

The relationship of resistance: 1 r = 1 r1 + 1 r2

19. Calculation of electric work: w=uit

20. The definition of electric power: p=w t

Common formula: p=ui

21. Joule's law: q amp = i2rt

For purely resistive circuits: q amp = i2rt

u2t/r=uit=pt=uq=w

22. Calculation of the total power of the lighting circuit: p=p1+p1+......

1. Quality m

2. Temperature t

3. Speed v

4. Density

5. Force (gravity) f

6. Pressure p

7. Power w8, power p

1. Force (f): Force is the action of an object on an object, and the action of force between objects is always reciprocal. Unit of force: Newton (n).

2. The three elements of force: The magnitude, direction, and point of action of force are called the three elements of force. The diagram of the force should be scaled; Schematic diagram of the force, not scaled.

3. Gravity g: The force experienced by an object due to the attraction of the earth. Directions:

Straight down. Gravity and mass relationship: g=mg m=g g, g=kN. kg.

Reading: Niu Xiang This kilogram of silver means that the gravity of an object with a mass of 1 kilogram on the earth is a cow.