Junior High School Physics If you have a problem, please ask the teacher for advice!!

1) Of course, it is possible for an object to be electrically charged, and when an object has an opposite charge to the straw, they can attract each other due to the mutual attraction of different charges; It is also possible that the object is not charged, the straw is charged, the charged body has the property of attracting light and small objects, the object is a light and small object, and it will be attracted by the charged straw;

2) Hair and rubber rod rubbing, rubber rod is negatively charged, in fact, rubber rods, plastic combs, straws are similar in material, have a strong ability to bind electrons, so they are usually easy to get electrons when rubbing, negatively charged!

1) No, you can't. Because an object close to a charged object will induce an electric charge, it will be attracted because it will generate an opposite charge at the end of the charged object.

2) The glass rod rubbed with silk has a positive charge, so the straw has a negative charge, and the napkin has a positive charge.

The former is because the straw is attracted, and the latter is because the charge is conserved (the sum of positive and negative charges is 0)3) The tissue loses electrons, and the straw loses electrons.

The object is of course possible to be electrified! the opposite charge of the straw; It is also possible that it is not electrified, the straw is electrified, and it is a light and small object, of course, it can be attracted to an uncharged object, just like an iron rod close to a small magnetic needle, the magnetic needle can be attracted by the iron rod, is the iron rod necessarily magnetic? Not necessarily!!!

It's hard to say who is positively charged and who is negatively charged when the straw rubs against the napkin, and the exam will not be tested! It depends on whose nucleus has the ability to bind electrons, with those with strong electron binding ability easily gaining electrons and weak losing electrons.

1.There are cations in a mobile, conductive solution.

2.At this time, it is the electrons that are transferred (negatively charged).

3.It depends on how humid the air is.

4.No, sometimes two physically bound electrons have similar skills, so they can't be triboelectrified5No, when the charge distribution is balanced, it does not move.

6. Only a large amount of dissimilar charges can produce such a phenomenon.

7.Definitely not.

8.The original fog of the cold air disappears slowly, and the fog may worsen, which is avoided by turning on the warm air.

1.The positive charge is the nucleus, hcl, sulfuric acid, etc., h+ are all moving.

2.It is only the electronics that move, and the electronic part moves to the object to be measured, causing the electroscope to become macroscopically negative.

3。An uncharged object is macroscopically positively and negatively identical and an insulator just makes the experiment more accurate because not insulating may cause the current to break down the air.

4.No, only materials that can capture electrons after friction will be electrified.

5 Not because the charge will be macroscopically "uniformly" distributed across the slide.

6 The reason for this phenomenon is that the negative and positive nuclei are first "neutralized" and then because there are fewer electrons than the positive charge, the electroscope fragment finally becomes positive and opens.

7。It's 0°, it's not 1°, it must be 0° in the steady state, because the water becomes icy, and the ice becomes water, and it needs to release or absorb a lot of heat, and the weak effect is not enough to make it change a lot, so it's 0°

8 is caused by turning on the warm air, it should be water vapor in the air, and the water vapor content in the warm air is high, and it turns into water when it is cold, of course, if the temperature of the warm air is high enough, so that the windows are heated together to make it higher than the temperature of water vapor condensation, the natural water droplets will disappear.

1.The positive charge in the metal does not move, just the electron, the electroscope belongs to the metal. But in other cases, the positive charge can move, such as positive ions in solution.

2.The positive charge on the electroscope is that the positively charged object sucks up the negative charge in the electroscope, so that the electroscope carries a positive charge.

3.Air is an insulator, and insulators do not conduct electricity easily, i.e., they do not take away electrical charge.

4.No, in general, two objects made of different substances rub against each other to cause electricity, but the same matter does not.

5.No, once the balance is reached, the charge does not move arbitrarily.

6.The negatively charged foil closes because the positive charge on the object neutralizes the negative charge, and then the positive charge on the object continues to transfer to the foil, causing the foil to take on the positive charge again, causing it to reopen.

7.Under normal circumstances, the temperature of a pure ice-water mixture is zero degrees Celsius.

8.In winter, the temperature in the car is high, the humidity is high, the temperature outside the window is low, and the window glass is the lowest temperature in the car, so the water vapor in the car liquefies into water droplets on the glass.

1.Both positive and negative charges move, and their movement forms an electric current! Whereas, in physics, it is stipulated that the direction of movement of a positive charge is the direction of the current.

2 This question is uncertain.

34 It's not.

5 No, just reach the balance.

6 The positive charge neutralizes the negative charge, so it closes, and then the positive charge moves to reach the equilibrium of the electroscope and the object, and then the electroscope carries the positive charge again, so it opens again, and the working principle of the electroscope is that the same kind of charge repels each other.

7 The temperature of the ice-water mixture is 0 degrees Celsius at standard atmospheric pressure, and of course it depends on the pressure.

8 In winter, there will be water droplets in the car window, this is because the outside temperature is low, so the temperature of the glass is also very low, the water vapor in the car is formed by liquefaction after cold, the heater is to make the liquefied water droplets speed up the evaporation rate, and the temperature of the glass becomes high, the water vapor can not be liquefied, some questions I don't understand what you want to express, so I didn't answer, I hope my answer can bring you some help.

1. Movement (there is definitely movement), but the positive charge does not move directionally.

2. It will not move, it is a negative charge that moves.

3. Air is a poor conductor of electricity.

4. Theoretically, yes, but the excess charge of good conductor friction cannot be stably preserved.

5. No, the same sex repels each other, and the excess charge gathers at the tip.

6. Closing represents neutralizing the charge, so it is positively charged.

7. Under a standard atmospheric pressure, the temperature of the ice-water mixture is 0 degrees Celsius 8, the water droplets are formed by the cold of hot air, and the water vapor is on the inside of the glass, and the high temperature is required to speed up the evaporation, so the effect of hot air is obvious.

1 can not 2It's all electrons that move back and forth.

3.Air is usually an insulator.

4 Yes, but the conductor is electrified and gone.

5.Once equilibrium is reached, the electrons will not move.

6.First it neutralizes, then it closes, and then it opens again with the same charge.7It doesn't have to depend on the size of the air pressure.

8. Let the water absorb heat and vaporize into water vapor.

1.Can a positive charge move?

It can be moved, such as the positively charged cation in the solution can be moved; In metals, electricity is conducted by free electrons.

2.If it can be moved, then put on the electroscope, is the positive charge in the atomic nucleus moving to the electroscope, or is the positive and negative charges attracting the negative charge in the electroscope to the object to make the electroscope positively charged?

It is the attraction of positive and negative charges, which draws the negative charge in the electroscope to the object, so that the electroscope is positively charged.

3.Why is the charge in the electroscope not lost in the air? What does it have to do with insulators?

Because air is an insulator, free electrons cannot move in the air.

4.Does all object friction cause electricity?

Not necessarily, it depends on the ability of the object to gain and lose electrons. That is, it is related to the order of frictional electrification of the object, and it is also related to the friction strength.

5.If the object is not removed, will the limited electrons move back and forth between the electroscope and the object, causing the slide to open and close?

Electrons don't move back and forth, and they don't move when they're in balance.

6.Why is it that when the electroscope is negatively charged, the object is in contact with it, and it is found that the electroscope slide is closed first and then opened, and the object must be positively charged?

The electroscope is first neutralized with positive and negative charges, and then opened with positive charges;

7.Does the temperature of the ice-water mixture have to be 1 degree Celsius?

At standard atmospheric pressure, the temperature of the ice-water mixture must be 0 degrees Celsius. , which is the basic regulation of Celsius.

8.Why is there no cold air on the water droplets on the car window in winter, but a warm air?

The water vapor in the car liquefies into water droplets when it encounters cold glass.

1. A positive charge can move.

2 is moving with a negative charge.

3 will be lost into the air if the air is humid 4

1. It depends on how to move, according to your 2, what you understand should be the positive charge in the nucleus, that is, the proton, which is immovable. If it's a positive ion, it can move. 2. The object should be positively charged and lacks electrons, so that the electrons on the electroscope are taken away, so that the electroscope loses electrons and is positively charged.

Electrified reason: lose the electron display positively charged, get the electron negatively charged) 3, the electron can not move freely in the insulator 4, two kinds of objects with different electron binding ability can rub each other to be electrified (there is a loss of electrons) 5, the electron will not "run around" after reaching the electrostatic equilibrium 6, if negatively charged, it will be larger, positively charged, it will be neutralized first, and then positively charged, first reduce the net charge, and then increase 8, because the higher the temperature, the greater the saturation pressure.

9. The points you give are a little less......

1. Yes, in addition to charged ions, positrons also exist.

2. Due to friction and electricity, there is neither cation nor positron, and only the positive and negative charges attract the negative charge in the electroscope to the object, so that the electroscope is positively charged.

3. Yes, but this situation is very small, and it is related to air humidity and dust. For example, this situation is particularly obvious in some metal material processing plants, where there are many conductive substances in the air, and there is also an external electric field.

4. Two identical substances rub against each other, and it is quite difficult to generate electricity due to the ability to bind electrons. However, if an excess amount of external heating energy is given, it is possible to ionize the substance. But I think friction in the general sense is very difficult to do.

5. The charge goes back and forth in the conductor, and only the electromagnetic effect can be generated, and the structure of the electroscope does not have this condition. The non-stop opening and closing of the metal sheet is accompanied by the conversion of mechanical energy (in this experiment, the charge will eventually be evenly distributed, so it will not open and close constantly. )。

You can only do this by constantly inputting electricity, otherwise this thing can be used as a fan when it gets bigger.

6. Due to the negative charge before, when we put the object with a positive point, the negative charge on the two blades will be neutralized, and the Coulomb force between the two blades is zero. Over time, more positive charge moves to the blade, at which point the same pole repels and the leaf opens again.

7. We define the melting point of ice cubes at standard atmospheric pressure to be 0 degrees Celsius. Because of the presence of ice and water in the ice-water mixture, endothermic will cause the ice cubes to melt to maintain the temperature, and exothermic water will condense into ice and release heat to maintain the temperature. But the change in temperature is gradient and not uniform in the water.

Only at the junction of ice and water is 0 degrees Celsius. So we measure the temperature of the general ice-water mixture between 1-4 degrees.

8. The water droplets on the windows in winter are due to the high humidity and high temperature inside the car and the low temperature outside the car. Therefore, at the car window, the low temperature outside will cause the water vapor in the air to condense into water droplets.

b The buoyancy of the wooden ball is the largest, the iron ball and the copper ball sink to the bottom, buoyancy + support force = gravity, and the gravity of the wooden ball = buoyancy, and the gravity of the three is equal, so the buoyancy of the wooden ball is the largest.

Pick B. After the three balls are put into the water, the iron ball and the copper ball sink to the bottom, and the buoyancy is less than the gravity; The wooden ball floats, and the buoyancy is equal to the gravitational force. And the mass of the three is equal, and the gravity is also equal. Use gravity as a reference quantity for the magnitude of buoyancy.

The iron ball and the copper ball will sink to the bottom and be subjected to three forces respectively: gravity, ground support force, and buoyancy, so the buoyancy force is less than the gravitational force; The wooden ball floats on the surface of the water and is subject to buoyancy equal to gravity. So the wood ball is most buoyant, b pair.

1.The object will move in a uniform linear motion only when the force is balanced;

2.Generally, the force of an object is analyzed from two dimensions: horizontal and vertical;

3.Therefore, since it is a uniform linear motion, there are generally two pairs of equilibrium forces - horizontal and vertical;

4.In this problem, the force in the horizontal direction of the train is resistance and traction (which can be simply understood as the force that pulls the train forward), and the vertical direction is the gravity of the train and the support force of the rails on the train. So the magnitude of traction is equal to the magnitude of drag, and the direction is opposite.

Gravity and support balance.

5.Traction does not refer to speed. For details, please refer to it.

The resistance is a multiple of its own weight, so the resistance = 294000N, because it is a uniform movement, the force is balanced, and the resistance and traction are a pair of balanced forces, so the resistance is equal to the traction force. s=vt=180*1 (note the uniform unit).

The gravity of the car is balanced with the support force of the ground for the car. Traction is a force, not a velocity, and is a force that opposes the direction of drag. Why don't you ask the teacher if you have a question? It would be better to answer in person.

1。Driving at a constant speed shows that the traction force = the drag of the train ff = f pull = 14700000*

s=v*t=180km h*1h=180kmThe gravity of the car is balanced with the support force of the ground.

Traction refers to overcoming the friction of the ground against the vehicle.