Q.1 Why don’t we remember dreams?
Dreams are usually stored in the short term memory. If you want to remember your dream, you have to try to recall them within the first 5 minutes of waking up or they are usually didn’t recalled. A normal person sees about 10 dreams in a night but it is quiet hard to recognise them. You can only remember every dream if you wake up during or immediately after each one. While you sleep, your brain doesn’t just turn off. It goes through several stages of sleep, including REM (Rapid Eye Movement), sleep. In this stage of your sleep, your eyes move back and forth under your closed eyelids.
During REM sleep, you have dreams and sometimes those dreams can be scary or brings down your mental balance. At nearby 1.5 hour, it changes automatically between non-REM sleep and the REM sleep. The quantum of time spent in rapid eye moment sleep rises with each sleep cycle through out the night. The longest periods of REM sleep occurs towards morning. If you wake up during this REM stage, it isn’t that much difficult for you to recognise what you were dreaming about.
Q.2 Why does smoke not fall down?
According to Isaaac Newton’s primary law, if we throw anything upwards, it comes down due to gravitational force present in earth. Instead the smoke doesn’t come down because it is a colloid – a substance that is microscopically distributed throughout another substance. It is a combination of airborne liquid, solid and gas. When smoke is emitted, blends with the air in the atmosphere and hence becomes part of it.
Further, since the density if smoke is less than that of the surrounding air, it rises. It is the same with a balloon, which also rises as the air trapped in it has less density than that of the surrounding air.