In lightning , light is seen first and sound is heard later it is due to 1)optical illusion
2) variation in temperature
3) position of observer
4) difference of velocities of light and sound

What was the approximate temperature of the universe at an age of 1015 s?

Remote controls rely on to carry signals and transmit information over short distances.

Onsider a u-tube whose arms are open to the atmosphere. now, equal volumes of water (ρ = 62.4 lbm/ft3) and light oil (ρ = 49.3 lbm/ft3) are poured from different arms. a person blows from the oil side of the u-tube until the contact surface of the two fluids moves to the bottom of the u-tube, and thus the liquid levels in the two arms are the same. if the fluid height in each arm is 31 in, determine the gage pressure the person exerts on the oil by blowing. (round the final answer to three decimal places.)