Hello…can somebody answer this weird question…My physics teacher ask me about this question but he actually doesn’t know the answer…His question is about a person who occured a falling elevator. When the elevator falls, is that posibble the person will knock his head on the elevator ceiling? If we think logically, a tall person maybe knock his head when the elevator falls but what if a short person is in the elevator? Is it related to a person’s height? Or maybe the person will not knock his head on the elevator ceiling?
My feet have never left the floor in an elevator. I don’t know much about physics , but I would think that the elevator would have to descend faster than a falling body to hit your head on the ceiling.
Elevators travel at a fairly constant velocity, which is why no one goes flying about when they descend. If you’re ever in a very fast elevator, herman_and_bill, you might notice that you feel a little lighter for a moment while it accelerates downwards. If it were to continue accelerating at 9.8m/s[sup]2[/sup], (the acceleration due to gravity on earth) then you would start floating as if there were no gravity in the elevator. This wouldn’t force you to bang into the ceiling, though.
Eventually, there’s two options:
-
The elevator crashes into the ground. The sudden deceleration causes you to hit the ground very hard and may crush the elevator car altogether.
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The elevator reaches terminal velocity, due to air resistence, and stops accelerating. Your weight would return and you’d be standing on the floor again. And then the elevator would crash, resulting in No. 1, above.
Of course, real elevators have emergency brakes and stuff. 
The answer is no, when the elevator is in free fall, the person will be appear to be ‘weightless’ in the elevator and will not hit hios head, but the accelration will slow down to zero eventually due to air resistance, so the persons weight will appear to be reduced but will still be acting in a downward compared to the elevator postion direction until it reaches terminal velocity when your weight would appear normal.
The only way to hit your head against the ceiling would be if the elevator was accelrating downwards faster than g.
If your elevator had an engine that would drive it downwards with an acceleration of 2g, for example, you’d smack the ceiling with the full force of your body weight. A downward acceleration of 1.01g, on the other hand, would cause you to slowly drift upward.
In a free-falling elevator, though, the only way you’d hit the ceiling is if you pushed against the floor.
People in a spacecraft in orbit, or in the KC-135 (the so-called Vomit Comet)
are in almost the same situation as someone in a falling elevator-
you will find that if they are untrained and inexperienced, they regularly hit the walls and ceilings,
sometimes gently, sometimes not-
mostly because untrained people are not well adapted to weightless conditions.
SF worldbuilding at
http://www.orionsarm.com/main.html
See this Cecil column from a few days ago.
Hiii…me again…actually i don’t understand the concept of the gravity accelaration…i learn one thing that W=mg but when we have to use that formula? Is it when we have to measure our weight only? Sometimes, I got some questions regarding to the topics like for example, a force exerts on a box. If I said the force exerts on the box is 5 N and the box’s weight is 10 kg…so what is the net force for that box if we neglect the friction force and air resistance? Is it possible the box will move?
You can use that formula to find any of the values used for the calculation as long as you know the other two. For instance, if you know the mass of an object as well as its weight, you can determine the gravitational exceleration it’s exposed to.
Example: if an object on the moon has a mass of 10kg, and a weight of 16.2N, you can calculate the gravitational acceleration caused by the moon.
Well, the net force on the box depends on the direction of the 5N force. To lift the box straight up would require a force of more than 98N (which is the force applied to a 10kg object by earth’s gravity). However, if you ignore friction entirely, then any force that is applied at an angle to the normal (i.e. not straight up or straight down), will cause the box to move.