This web article is reviewing an electric motorbike that can go from 0 to 60 MPH in under one second. In comparing the accelerating of the bike, the article says:
All this gives the driver a G-force three times more than that faced by a skydiver during freefall!
Er.. come again?
G-force, the way it is used for the public, is simply the amount of "reaction" force that we feel. When doing a looping roller coaster, it is the amount of force the seats exert back onto us. That's why at the bottom of a loop, you get G-force greater than "g", the gravitational acceleration at the earth's surface (9.8 m/s^2), while at the top of a bump, you could get "negative G's", meaning it is less than g.
So what's the G-force experienced by a skydiver? If you ignore air resistance, it should be.... er... ZERO! Free falling, by definition, implies that there's no reaction force. That's how the "vomit plane" works when people are training for weightless environment - the plane makes a free fall every few minutes, and every entity in the object will feel no reaction from the floor of the plane since everything is free falling. So equating the bike's acceleration as having three times the G-force experience by a skydiver is rather puzzling.
Now, one could argue that maybe the writer was thinking about the G-force experienced by the skydiver after he/she reaches terminal velocity, which would make the G-force to be equal to g. Assuming that the writer is smart enough to know basic mechanics AND know about terminal velocity, then the comparison is also puzzling. If it is just a simple "g", then why not compare it to the regular person standing still on the ground? After all, it IS the same thing and I'm guessing, A LOT more people are more familiar with standing still on the ground than skydiving.
Nope. I think this is a mistake of comparison.
Zz.
7 comments:
Here is my post on weight and apparent weight. Quite appropriate for this discussion.
http://blog.dotphys.net/2008/09/gravity-weightlessness-and-apparent-weight/
Who but a Physicist ever ignores air resistance? A skydiver who calculated their terminal velocity without air resistance, with or without their parachute open, presumably wouldn't jump. Perhaps a spherical cow would jump. But classic, of course.
Did you even READ the rest of the blog? Look at the scenario I presented in the SECOND case where there is terminal velocity. What do you think is involved THERE? Antigravity?
Oy Freaking Vey!
Zz.
"A skydiver who calculated their terminal velocity without air resistance"
terminal velocity exists because of air resistance. without air there would be no terminal velocity. what a stupid comment. who but a ignoramus would say such a thing.
"A skydiver who calculated their terminal velocity without air resistance"
terminal velocity exists because of air resistance. without air there would be no terminal velocity. what a stupid comment. who but a ignoramus would say such a thing.
I think the person meant, how many g's does a person feel when reaching terminal velocity and then PULLING THE CORD. How many G's are felt as the parachute opens up??
But that isn't FREE FALL!
Zz.
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