How to learn physics well in the second year of junior high speed calculation .

The summary is the most important, including the summary of the classroom teacher, the summary of the self-preview review after class, the summary of the wrong questions, it is best to find a book, record the experience, usually turn over more, for the formula, the memory also needs to be understood, according to the specific situation appropriate use, pay attention to the scope of application of the formula.

Don't equate physics with mathematics, especially calculate problems to develop a good habit of writing format.

For most problems, the diagram is quite important, the key to the electrical circuit diagram is to simplify, we can distinguish the connection situation at a glance, the force analysis of mechanics is the basis of the problem, the optical path diagram can help us analyze the problem, and even the boiling evaporation of heat will use the diagram.

Of course, it's easier said than done, but don't be stressed.

I think the key to physics is to get started, and touch classes will be bypassed.

Physics is very interesting.

Personal experience: If you feel that your foundation is poor, you should first read the book, memorize the formulas, know under what circumstances each formula can be used, and then do some simple questions first, and then slightly more difficult questions to consolidate your knowledge. Those off-topic, difficult questions, and strange questions don't have to be done, but if you learn very well, it doesn't hurt to do it, but before that, doing that kind of question is a waste of time and energy, and it will also hit self-confidence, after all, questions like the college entrance examination don't account for much of the score, in short.

Books are to be read, questions are to be practiced, and don't be in a hurry, physics is not something that can be learned in a day or two, and if you stick to it, you will see results.

Good luck!

Understand the principle, as well as the factors that affect velocity, such as the magnitude and direction of acceleration, as well as memorizing the formula, and the deformation of the formula.

The principal unit of density is kg m 3.

Commonly used density sheets are: t m 3;kg/dm^3；g/cm^3.

t::mass unit "ton").

Conversion relationship: 1t m 3 = 1kg dm 3 = 1g cm 3 = 10 3kg m 3.

So, in the unit of density, the main unit is kg m 3, which is the small unit. The rest of the units are large units.

Moreover, several large units are equal, all 1000 times larger than small units.

Physical significance: 1t m 3: the mass of each cubic meter is 1 ton; Or the volume of a substance with a mass of 1 ton is 1 cubic meter.

1kg dm 3: the mass of a substance with a volume of 1 cubic decimeter is 1 kg; Or the volume of a substance with a mass of 1 kilogram is 1 cubic decimeter.

1g cm3: The body is 1 cubic centimeter and the mass of a substance is 1 gram; Or the volume of a substance with a mass of 1 gram is 1 cubic centimeter.

Conversion process: 1t m 3 = 10 3kg m 3.

1t/m^3=10^3kg/dm^3=1kg/dm^3.

1t/m^3=10^6g/106cm^3=1g/cm^3.

Conversion method: When the unit is changed from small to large, the original number remains unchanged, as a multiple, multiplied by the positive exponential power of ten (or multiplied by the advance rate);

When a large unit becomes a small unit, the original number remains the same, as a multiple, multiplied by a negative exponential power of ten. (or divide by the advance rate).

Examples: 1) Find out that the density of a substance is grams cubic centimeters kilogram cubic meters.

2) The mass and volume given in the question are grams and cubic centimeters, and they are fill-in-the-blank and multiple-choice questions, so the density unit is gram cubic centimeters. p = kilogram cubic meter gram cubic centimeter.

1 meter per second = kilometers per second.

1 meter per second = kilometers per minute.

1 meter per second = kilometers per hour.

When the time units are the same, only the base units of the meter are converted.

When the distance units are the same, only the time units are converted.

1 meter per second = 1 10 -3 kilometers per second.

1 meter per second = 6 10 -2 kilometers per minute.

1 meter per second = kilometers per hour.

1 km per second = 1 10 3 m per second.

1 km per minute = 50 3 meters per second = meters per second.

1 km/h = 1 meter per second = meter per second.

1.Smaller. When the current scale is larger, the total resistance of the whole circuit is smaller, and the resistance r resistance made of metal materials is smaller. As can be seen from Figure A, the temperature corresponding to a small R resistance is low.

Resistance box resistance r'=450, the corresponding current at the space in Figure C is the largest, so the resistance of the whole circuit is the smallest, and the resistance r made of metal materials is the smallest, and the minimum value of the resistance r is 100 and the corresponding temperature is 0

1. Smaller. If the temperature is high, the r-resistance value is large, so the current is small; Vice versa. Therefore, when the current is large, the r-resistance value is small, and the temperature is small.

The voltage is 3V and the current is 5mA, so the total resistance value is 600 ohms, at this time R is 600-450=150 ohms, so the temperature is 50 degrees.

The higher the current, the smaller the resistance, notice that the resistance is proportional to the temperature, so the lower the temperature, fill in "less".

When r'=450

r+r'=v/i=3/

r=150, we can see that the relationship between r and t is r=t+100=150t=50 degrees.

The micro wind fan works through the strong action of the magnetic field on the electric current, so it has a magnet and a coil inside, and the rotation of the blades causes the coil and the magnet to have electromagnetic induction, which generates an electric current to make the bulb shine.

The knowledge of the third year of junior high school, why do you have to explain it in the second year of junior high school?

1) Xiao Liu measures the fixed resistance voltage, and Xiao Li measures the sliding rheostat voltage.

2) Rx = 1V ohms.

Power supply voltage = 3V + 3V = 6V (take special cases, when the RX sliding rheostats are all 3V, then the sum of their voltages is the power supply voltage.)

You're a fast learner. We only learned it in the third year of junior high school.

This is an electromagnetic induction phenomenon.

It is the conductor cutting in the magnetic field and the induced current generated by the movement of the magnetic inductance line makes the small bulb glow.

Because there is no power supply for this device itself, turning the fan converts kinetic energy into electrical energy and does the movement of cutting magnetic inductance lines, which is an electromagnetic induction phenomenon.

Time = distance speed, speed per hour is instantaneous speed, can not be used, should use the average speed, before speeding up, the time from Ningbo to Wuchang is: 1100km 80 (km h) = hours, save time = hours.

First, according to the distance = time * speed, calculate the distance from Ningbo to Wuchang is 200km h*9h=1800km, and then by time = distance speed, you can calculate the time from Ningbo to Wuchang before the speed increase is 1800km 80km h=, so the time saved.

Time saved t=1100 80-9=hours, 200km h is the interference term in this problem.

1. Known: s=17m; v1=680m/s；v2=340m s to find s1

Solution: S1 = V1t = 680m S*(17m 340m S) = 34m Answer: The bullet advanced 34m.

2. Known: v=340m s; s=2720m；v1 = Find: s1

Solution: s1 = v1t = v1 (s v) = 510m s*(2720m 340m s) = 4080m

A: The plane has flown to a place of 4080m ahead.

Hello because the speed of the bullet is 2 times that of the sound in the air, the distance of the bullet in the same time is also 2 times that of the sound, so it is 34m

The second question is similar to the previous question, it is a multiplication, so multiply it by 2720m to get 4080m.

Known : v = 108km h = 30 m s ; l0 = 300 m ；l = 3km = 3000 m

Solution: From the bridge on the locomotive to the tail of the train leaving the bridge, the train crossing the bridge is completed, so the distance of the train crossing the bridge is l0+l=3300m

t = (l0+l) v = 3300 30 s = 110 sA:.

Calculation of average speed in junior high school physics.

Cheetah 40m s

Brown petrel 5000 60=

Sailfish 108

The answer is brown petrel fast.

Conversion: 5km=5000 = 60=83 m/s, 108kmh=30m/s so compare yourself.

5000/60=250/3m/s

So the answer is clear.

40 m x 60 x 60 = 144,000 m = 144 km 5 km x 60 = 300 km 300 144 108