Junior High School Physics Problems Help

4.Inverted miniature reality. If you don't understand, I'll explain it to you!

Reason: When the image presented on the light screen is an inverted magnified reality, the object distance at this time is: 2f>u>f, and the distance is:

v>2f.If the position of the candle and the light screen is reversed, the object distance becomes u>2f, and the distance becomes 2f>v>f, and the image on the light screen is an inverted and reduced reality. (Got it?)

5.The original stamp is also upright.

Reason: The magnifying glass becomes an upright illusion of magnification.

7.Solidification Cause: The process of changing from water to solid is called solidification.

10.Free electrons Free electrons.

11.Consider this question in two scenarios;

1): Consider from the outside of the battery: positive electrode --- electrical appliance --- negative electrode.

2): Consider from the inside of the power supply: negative --- positive.

4.It's still the same, you can see the real image of the handstand and magnification.

5.The stamps are upright.

7.Congeal. 10.Free electrons Free electrons.

11.Positive electrode Electrical Appliance Negative electrode.

The first one upstairs was wrong.

4.Get the reality of handstand, shrinking;

5.What he saw was the reality of the stamp standing upright, magnified, and the stamp standing upright;

7.Congeal. 10.free electrons; free electrons;

11.The positive electrode flows out and flows back to the negative electrode through the electrical appliance;

4.Get the reality of handstand, shrinking; Basis: The distance becomes 2f>v>f, and the image on the light screen is an inverted and reduced reality.

5.The stamps are also upright.

7.Coagulation 10free electrons; free electrons;

11.From the positive electrode it flows through the electrical appliance back to the negative electrode.

The last one upstairs was wrong!! There can't be a second one!!

(1) It is also possible on the moon, regardless of location.

2) Can be tilted. However, the pull direction must be parallel to the scale axis.

3) Friction does not have to be resistance, but can also be power.

4) Hang the spring dynamometer on the rope, pull down with a force of 4n, and the spring dynamometer shows 4n, then the spring dynamometer is regarded as an object, and its pulling force on the rope is 4n. Therefore, the tension of the rope to the spring is also 4N, and then the tension of the rope to the spring is regarded as the left tension, and the tension of the hand is regarded as the right tension.

5) Not very clear.

6) The rear wheels of the car actively rotate, giving the ground backward friction, and the ground giving the rear wheels forward friction.

7) Because the athlete is in a state of motion, when he reaches the finish line, he must continue to maintain a state of motion, so he cannot stop immediately.

1.Yes, gravity only has an effect on gravity and has no effect on other physical quantities. Gravity is not elasticity, it is an attraction.

On Earth, the magnitude of gravity is equal to the magnitude of the pulling force, but this does not mean that gravity is the same as the pulling force. On the Moon, weigh the object, and the displayed value becomes smaller. But you directly pull the spring hard and say, there is no problem with the measurement.

2.Spring dynamometer.

It does not have to be pulled vertically, the title means that it is pulled horizontally along the axis of the spring dynamometer.

3.In fact, there is not the slightest relationship between drag and friction, which can be resistance, power, or resistance. Whereas, the resistance can be frictional or not.

Let me give you an example of each of the 4 situations I mentioned above, and you will understand.

2）.Friction is the driving force: a wooden block is placed on the table, and when we push the wooden block with enough force, this can happen: the wooden block drives the table forward together. At this time, if there is a relative displacement between the wooden block and the table, there is a difference between them.

Sliding friction.

If displacement does not occur, it exists.

Static friction. That is, there is friction between the wooden block and the table. And this friction is the power relative to the table. Because it's this friction that drives the table to move.

3）.The resistance is friction: needless to say, this is the case, where the wooden block slides on the table.

The resistance relative to the block is the friction between the block and the table.

4）.Resistance is not friction: the block moves on a flat surface and stops when it hits the wall.

At the moment when the wooden block stops, the wooden block goes from having speed to no speed, and the wooden block is stopped by a certain resistance, and this resistance is not friction, but the thrust of the wall against the wooden block.

4.Force gauge on springs.

The left and right sides of the force are each exerted 4n, the left stressed object is the pull ring, and the right stressed object is the spring. Toward.

When the ring applied force, it did not cause.

Spring dynamometer.

The change of the indication and the application of force to the spring causes the spring.

Elastic deformation. and causes the change of the indicator, so the indicator is 4n.

5.The plastic sleeve is tightly covered.

On the handlebar, the pressure on the handlebar is increased, and if the pressure of the plastic sleeve on the handlebar decreases, then the plastic sleeve is easy to fall off, so it is said to increase the pressure.

6.The rotation of the rear wheels of the car is to give the ground backward friction, then the ground gives the rear wheels forward friction.

7.After the athlete reaches the finish line, the foot stops moving, and the upper body still maintains the original movement state due to inertia, so it cannot stop.

(1) It is also possible on the moon, regardless of location.

2 Because springs also have gravity.

3) Friction is not necessarily resistance, it can be power.

4 Not very clear.

5. There is also a decrease in the force area, which is to increase the friction by increasing the pressure, and the power is facing forward after 6.

7 Any object has mass.

Where there is quality, there is inertia.

Inertia is the continuation of the original state of motion.

1) Because how much tension the spring is subjected to, how much elongation it will have, regardless of the position.

2) The title is wrong, only the gravity must be measured vertically, and the other forces must be measured in the direction of the force.

3) Friction is not necessarily resistance, friction can be power, for example, people walking, and the friction given by the ground is the driving force for people to walk.

4) If the indication is 0, it means that the spring is not elongated, if you think about pulling both sides, can the spring not be elongated?

5) The plastic sleeve is tightly set on the handlebar, which increases the pressure on the handlebar, so it is difficult for the plastic sleeve to slip down, which increases the friction.

6) The rear wheels actively rotate, giving the ground backward friction and the ground to the rear wheels.

Forward friction.

7) The athlete is in a state of motion, and when he reaches the finish line, he cannot stop immediately because he has to continue to maintain the state of motion due to inertia.

At the beginning, there was water on the egg, and the water vaporized to absorb heat, so it was not so hot, but later there was no water, and the heat inside the egg was released, so it was very hot.

Because the burning of cotton consumes oxygen, creating a pressure difference between the inside and outside of the bottle (large on the outside and small on the inside), the atmospheric pressure presses the eggs into the bottle.

Because adding salt to the water makes the water denser, the density of the brine is greater than that of the egg, so the egg floats.

1.I don't know 2Combustion consumes oxygen, the air pressure inside the bottle decreases, and the atmospheric pressure outside pushes the egg inward. 3.After adding salt, the density of the solution increases, and when the density of the solution is greater than the density of the egg, the egg floats.

1 When there is water on the eggshell, the water evaporates to absorb heat, and the heat mainly comes from the egg, and when the water evaporates, the egg is cooled mainly by the hand, so the hand will feel hotter.

2 When the egg is blocked by the bottle, the flame burns to consume the oxygen in the bottle, and can not be supplemented by the outside world, after the flame is extinguished, the pressure in the bottle is reduced, and the outside atmospheric pressure will press the egg into the bottle.

3 The density of the egg after the shell is greater than the density of the water The egg will sink slowly after entering. When salt is added to the water, the density of the brine is greater than that of the egg, and the egg will slowly float.

One:1(1) A: Use a scale to measure the length and width of the rectangular thin aluminum plate.

b: Use a balance to measure the quality of the rectangular thin aluminum plate.

C: The surface area of the rectangular thin aluminum plate is calculated, and the volume is noisy.

Correct. The thickness is calculated.

2) Length: L Width: N Mass: M

m/(ρl*n)

2.Length. Time.

Speed is wild. Acceleration.

Two: Because the trolley moves in a straight line at a uniform speed on the horizontal ground.

So its speed is always the same. v=