The "sharp and thin" voice of female students refers to the voice of female students______ This is because the vocal cords vibrate more when the female students speak______ For the sake of

The "sharp and thin" voice of female students refers to the voice of female students______ This is because the vocal cords vibrate more when the female students speak______ For the sake of

The characteristics of sound include tone, loudness and timbre; The "sharp and thin" voice of female students refers to the high tone of female students' voice; The size of tone is related to the speed (frequency) of object vibration. It is precisely because the vocal cords vibrate faster when female students speak, so the tone is higher
So the answer: tone, fast

Hawking, the giant who speaks with his fingers, the meaning of the end of the universe in the original text, the meaning of speaking with his fingers

The end of the universe here does not simply refer to what the end of the universe is or whether the universe has an end. It refers to the unknown and fascinating mysteries in the universe. Hawking's disease

Does the universe have boundaries? Where is the boundary of the universe? How does Hawking understand this problem?

Boundary is a proper term in physics. The "cosmic boundary" in Wu's mouth may refer to "boundary". For example, a two-dimensional sphere has no boundary, but your field of vision has a range, so there is a boundary. Our universe has such a boundary. Due to the limited speed of light, the limited age of the universe and the expansion of the space of the universe, The boundary we can see is a spherically symmetric region with a radius of about 40 billion light-years. The light outside this region has not yet reached the earth, so we can't see it. This is called the horizon of the universe. Beyond the horizon of the universe, no one can say whether space will extend infinitely. However, according to the observation results of microwave background radiation (the curvature of cosmic space is 0), Hawking's most important contribution to the Big Bang is to prove that under some special conditions, the expanding universe must start at a singularity. This is called the singularity theorem. Hawking also put forward a model that there was no time at the beginning of the universe, only space. Later, sometimes. Just like there was only South and no North at the North Pole. This is called "borderless condition", I'm glad that some non professionals like reading Hawking's books. I hope someone can translate Hawking's books more easily so that more people can understand them

1. An object a falls freely 20 meters above the ground, and another object B is thrown vertically at the speed VO on the ground directly below object A. what conditions should VO meet if AB meets when B falls? 2. A smooth inclined plane is 18m in total length. A small ball is released from the top of the inclined plane from rest and reaches the bottom of the inclined plane after 3S. If a second ball moves upward along the inclined plane at a certain initial speed while the ball is released, it rolls down after rolling for a certain distance. As a result, it reaches the bottom of the inclined plane at the same time as the first ball. Calculate the initial speed when the second ball rolls up 3. When an object falls freely from upstairs, the time taken to pass through a window with a height of 2 meters is 0.2S. How high does the object start to fall from the top of the window?

1. Find the critical point. When B goes up to the highest point, it can be seen that the following relative motion is that a approaches B at a uniform speed. Then the critical point is that ab lands at the same time. A landing time t = 2 seconds (20 = 0.5 * 10 * t * t). Then the single-sided operation time of B is 1 second. It can be concluded that V0 = 0.5 * 10 * 1 * 1 = 5m / s. then it can be known that they can meet when it is greater than 5m / s
2. First find the acceleration a, a = 2S / (t * t) = 36 / 9 = 4m / S ^ 2. At this time, the problem is the same as finding the critical velocity of 1. There is no solution here. You can solve it yourself
3. List the formula according to the question: 0.5 * 10 * T ^ 2-0.5 * 10 * (t-0.2) ^ 2 = 2 2t-0.2 = 2 T = 1.1s
This t passes through the T under the window, so the question = 0.5 * 10 * 1.1 * 1.1-2 = 4.05M

1: The trolley with a mass of 20kg travels 2.5m on a smooth horizontal road, and the speed increases from 10m / s to 12m / s. calculate the horizontal thrust on the trolley? 2: The output power of a crane is 50KW, and now the mass is 2.5 × How much work does the crane need to do when the weight of 10 (3rd power) kg is increased by 10m at a uniform speed? How long does it take the crane to finish the work? 3: The heavy hammer of the pile driver, with a mass of 25kg, is lifted to a height of 20m above the ground, and then let it fall freely (excluding air resistance). Trial calculation: (1) The gravitational potential energy of the hammer at the highest point? (2) What are the gravity potential energy, kinetic energy and velocity when the weight falls 15m?

The final vsquare - initial vsquare = 2aX can get the acceleration. Then f = A / m will know the thrust
2. V displacement without work P = f / V is 10 t = displacement divided by velocity
3.mgh
MGH MGH (2) e = 1 / 2mV square v = at

There are goldfish in the glass fish tank. Gently tap the upper edge of the fish tank with a thin rod, and the goldfish will be frightened immediately. At this time, the main way for the fish to receive sound waves is () A. Fish tank → air → water → fish B. Air → water → fish C. Fish tank → fish → water D. Fish tank → water → fish

Gently tap the upper edge of the fish tank with a thin stick. The sound is generated by the vibration of the fish tank. Therefore, the first sound transmission medium is the fish tank. It is transmitted to the fish through water, with less experience medium, and then transmitted to the fish through air and water, with more experience medium
Therefore, D