नजदीक आती रेलगाड़ी की सीटी की आवाज (तारत्व) बढ़ती महसूस होती है जबकि दूर जाने वाली रेलगाड़ी के लिए घटती जाती है। यह घटना किसका उदाहरण है?

Taking a glass of water and freezing it by placing it inside a freezer is an example of which type of change and process?

Which of the following statements is/are true about air pressure? (A) Air around us exerts very less pressure on us. (B) Air contracts on heating and expands on cooling. (C) Warm air rises up and cooler air tends to sink towards the earth's surface. (D) As warm air rises, air pressure at that place is decreased.