TEXT 1          From the clouds to a nearby tree or roof, a lightning bolt takes only a few thousandths of a second to split through the air. The loud thunder that follows the lightning bolt is commonly said to come from the bolt itself. However, the grumbles and growls we hear in thunderstorms actually come from the rapid expansion of the air surrounding the lightning bolt.
          As lightning connects to the ground from the clouds, a second stroke of lightning will return from the ground to the clouds, following the same channel as the first strike. Then the heat from the electricity of this return strike
raises the temperature of the surrounding air to around 27,000 degrees Celsius. Since the lightning takes so little time to go from point A to point B, the heated air has no time to expand. As a result, the heated air is compressed,
raising the air from 10 to 100 times the normal atmospheric pressure. The compressed air then explodes outward from the channel, forming a shock wave of compressed particles in every direction. Finally, like an explosion, the
rapidly expanding waves of compressed air create a loud, booming burst of noise.

TEXT 2
          Your joints can make a variety of sounds: popping, cracking, grinding, and snapping. The joints that “crack” are the knuckles, knees, ankles, back, and neck. There are different reasons why these joints “sound off”.
          The first is escaping gases. Scientists explain that synovial fluid present in your joints acts as a lubricant. The fluid contains the gases oxygen, nitrogen, and carbon dioxide. When you pop or crack a joint, you stretch the joint capsule. Consequently, gas is rapidly released, which forms bubbles. In order to crack the same knuckle again, you have to wait until the gases return to the synovial fluid.
          The second is movement of joints, tendons, and ligaments. When a joint moves, the tendon’s position changes and moves slightly out of place. Therefore, you may hear a snapping sound as the tendon returns to its original position. In addition, your ligaments may tighten as you move your joints. This commonly occurs in your knee or ankle, and can make a cracking sound.
          The last is rough surfaces. Arthritic joints make sounds caused by the loss of smooth cartilage and the roughness of the joint surface.

Answer the following questions.
1. What is the topic of text 1 and text 2 above?
2. Do you think that text 1 and text 2 above are explanation texts? Explain your answers by your own words.
3. Summarize the two texts in bahasa Indonesia.