Ask two junior high school physics questions, ask one junior high school physics question?

If both balls of equal volume A and B float on the water, then the buoyancy received by the two balls of A and B is equal to the gravitational force received by A and B respectively, but A and B are only equal in volume and do not know the density, so the amount of buoyancy they receive cannot be determined, so D is chosen.

The wooden blocks float on top of the alcohol and the wax blocks float on the water, indicating that the buoyant force they experience is equal to the gravitational force they are subjected to, respectively, because the wooden blocks and wax blocks of equal mass are known to be cThey are subjected to equal buoyancy.

d Because both balls are floating on the water, the buoyancy is equal to gravity according to the sinking and floating conditions, and the gravity and density of the two balls are not clear, so it cannot be judged.

c As above, buoyancy is equal to gravity, and since the gravity of the two objects is equal, the buoyancy is equal.

If you don't know how to speak, please ask Oh ( o

The conditions for floating are: g=f The volume of the first question is equal, look at the density, the mass with high density is large, the gravity is large, and the buoyancy is also large; According to Archimedes' principle, the amount of buoyancy is equal to the gravitational force of the water it distributes, and the amount of water discharged is more buoyant.

In the second question, C should be selected according to the floating conditions

1.If A and B are plastic balls and iron balls of the same volume respectively, although they are of the same volume and both float on the water, they are subject to different buoyancy, so D is chosen

2.Because both the wooden block and the candle are floating and have the same mass, the buoyancy is equal. Choose C

d c The first question does not know their gravity, nor does it know the v row.

Question 2: Both objects float, and buoyancy is equal to gravity.

d buoyancy and the gravity of the object are a pair of equilibrium forces, then the two forces are equal, and the density of the two spheres in the question A and B is not known.

c is the same as above.

Because according to Archimedes' law of buoyancy: the mass of the water discharged by an object when it enters the water is equal to the mass of this object, and since the density of the two spheres A and B is not known, the mass of the discharged water cannot be determined, so it cannot be judged.

Because the wax block is a mixture, its density cannot be known, so the reason is the same as above.

1 d is floating on the surface of the water, buoyancy is equal to gravity, I don't know the magnitude of gravity A and B, so it is impossible to judge.

2 c are both floating on the surface of the water buoyancy is equal to gravity and the mass is equal, so gravity is equal and buoyancy is equal.

The masses of two objects A and B are equal, the density ratio of A is 1:2, and the buoyancy ratio of them in water is 8:5.

Answer: First of all, judge the state of the object:

1. Assuming that A and B are in a floating state, the buoyancy should be equal, which is impossible.

2. Suppose A and B are in a submerged state, that is, suspended or sunk to the bottom. But the volume ratio at this point is equal to the reciprocal of the density ratio (because the mass ratio is equal to gravity, i.e., the mass is equal) 2:1 while the liquid density is equal, it is impossible for the buoyancy ratio to be 8:5

3. Excluding the first two possibilities, only the third situation is true, that is, A is in a floating state, and B is in a suspended or sinking state. Then the buoyancy of a and the gravity of a are multiplied by the volume of a by g, while the buoyancy of b is multiplied by the density of water multiplied by the volume of b multiplied by g

1. The sound is produced due to the vibration of the object, when the drum surface is pressed and held, the drum surface stops vibrating. So the sound is gone.

2.The vibration of the tuning fork on the right causes the air to vibrate, and then the tuning fork on the left vibrates to make a sound, and then bounces the ball, this experiment can show that the sound is produced by the vibration of the object, and it can also show that the air can transmit sound.

Because the vibration of the drum surface stopped.

The sound is produced by vibrations, and when the hand touches the drum, the drum stops vibrating and the sound disappears!

How is sound produced???

It's vibrating, so when you hold it, the drum doesn't vibrate, so it doesn't make a sound.

1.The sound is produced by the vibration of the object, and if you hold the drum face with your hand and the drum surface stops vibrating, the sound will disappear. 2.This phenomenon shows that sound is produced by the vibration of an object (the conversion method used).

1. 10ω 10ω 0a 10ω2.The resistance of the 1 to 2 1 to 1 1 to 1 2 to 1 wire is unchanged after it is made, even when the voltage is zero and the current is zero, the resistance is still constant, so it can be found by the formulas i=u r and r=u i.

The voltage and resistance are proportional, so the resistance ratio is the voltage ratio, and the current of the series circuit is equal everywhere, and the voltage on the branch of the parallel circuit is equal, so problem 2 can be solved

Hope to give you a satisfactory answer.

1. There is a wire, if the voltage of 6V is added at both ends, the current through it is, and its resistance is 10; If you add a voltage of 15V to it, the current in the wire is; At this time, the resistance of the wire is 10, if the voltage at both ends of the wire is zero, the current through it is 0; At this point it has a resistance of 10.

2. The resistors r1:r2=1:2, if they are connected in series to the power supply, the ratio of the voltages at each of their respective ends is 1:

2；The ratio of the currents passing through them is 1:1; They are connected in parallel to the power supply, and their voltage ratio is 1:1; The ratio of current is 2:1

1。Fill in the blanks with 10, 10, 0a, 10

2. The word is 1:2 1:1 1:1 2:1

10 ohms 10 ohms 0 amps 10 ohms 1:2 1:1 1:1 2:1

, the resistance is 10 ohms, i=u r, the current is , the resistance is 10 ohms, the current is 0, and the resistance is 10 ohms.

2.The ratio of voltage is 1:2 and the ratio of current is 1:1

The ratio of voltage is 1:1 and the ratio of current is 2:1

1.Do it with Ohm's law. r=u\i，6v\。According to the resistance unchanged (10), u r=i, 15v 10=,0

2.Serial positive and negative (resistance unchanged), 1:2, 1:2, 2:1, 2:1. If you don't understand, you can substitute a few numbers to go in.

2.(1) What is the design of the ballpoint pen to reduce the friction of the good school?

The balls of the ballpoint pen are in a rolling state during writing, which belongs to changing the sliding friction to rolling friction, reducing the friction and writing more smoothly (borrowed from the previous one).

2) What is the design of the ballpoint pen to increase friction?

The pattern on the barrel of the ballpoint pen increases the roughness of the contact surface, increases the friction, and makes the grip of the pen more envious.

The previous one's really good friend code.,I quoted it.,Mine should be added.。 ）

1. Ancient Egypt's rolling wood and boulders used to change the sliding friction to rolling friction, so as to reduce the friction of handling, 2. After the road surface splashed water and ice on the land, the ice surface was formed, and the ice was smoother than the ordinary roadside, which was used to reduce the roughness of the contact surface and reduce the friction.

3. The beads of the bead early chain hall pen are in a rolling state in writing, which belongs to changing sliding friction to rolling friction to reduce friction and write more smoothly.