题目

下列关于重力、弹力、摩擦力说法正确的是（ ） A . 因为物体本身就有重力，所以重力没有施力物体 B . 放在水平桌面上的两个球，靠在一起但并不互相挤压，两球之间也存在弹力 C . 两物体间如果有摩擦力，它们之间就一定存在相互作用的弹力 D . 根据 可知，动摩擦因数µ跟滑动摩擦力Ff成正比，跟压力FN成反比。Wind is the great maker of waves. There are exceptions (例外), such as the tidal (潮汐的) waves sometimes caused by earthquakes under the sea. But the waves most of us know are caused by winds blowing over the sea .Now let’s learn some physical (自然地理学的) things about it. A wave has height, from low point to high point . It has length (长度)--the distance from this high point to that of the following wave. The period of the wave means the time it takes for succeeding high points to pass a fixed point. None of these things stays the same--for all depend upon (依靠)the wind, upon the depth (深度) of the water and many other matters.The water that makes up a wave does not advance with it across the sea. Each drop of water turns around in a little circle with the passing of the wave, but returns very nearly to its original position (原先的位置). And it is lucky that this is so. For if the huge groups of water that make up a wave really moved across the sea, sailing would be impossible. If we want to find the speed of a wave, we may use the following way : Speed =" wavelength" × frequency (频率).Here, wavelength is the distance between two high points , frequency means the number of cycles per second 小题1:What causes waves?A．Earthquakes and nothing else. B．Only wind.C．Wind causes most waves. D．Wind causes some waves.小题2:Which of the following is TRUE according to the passage?A．The water of a wave moves away across the sea. B．The water of a wave remains almost at the same place.C．The water of a wave goes with the passing of the wave.D．The length of a wave means the distance from the top of a wave to the bottom.小题3:The speed of Wave 1 is 100 cm/s, frequency 10. The frequency of Wave 2 is 300, while its speed is twice that of Wave 1. Which of the following is right?A．The wavelengths of the two are equal.B．The wavelength of Wave 1 is 10 times longer than that of Wave 2.C．The wavelength of Wave 2 is longer than that of Wave 1.D．The wavelength of Wave 1 is longer than that of Wave 2.小题4:Where can we find this passage?A．music magazineB．fashion magazineC．scientist magazineD．sports magazine