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CSI - Acceleration or Velocity?
In the episode "Overload," in which Grissom investigates the falling death of a construction worker, he gets his facts mixed up. At the very beginning of the episode when they first go to the floor that the worker was on when he fell, Grissom says that "Terminal velocity is 9.8 meters per second squared. This guy would have hit the ground in 5 seconds." This sounds like pretty impressive knowledge, but 9.8 m/s/s (meters per second squared)is actually acceleration due to gravity, an entirely different value that concerns velocity change per unit time. Terminal velocity is the point at which no acceleration occurs due to air resistance, and is measured in m/s (velocity), not m/s/s (acceleration). It is a slip-up in itself that he would use an acceleration value to describe a point at which no acceleration occurs. Terminal velocity depends on the air resistance of the body, but it's about 120 mph, or 54 m/s, quite different from 9.8 m/s/s. And if he had hit after five seconds, according to Grissom's numbers, it would mean that he fell about 49 meters (and that's assuming constant "terminal velocity"), when, using the right numbers, the worker would have fallen about 123 meters. Grissom needs to brush up on his physics. (If I messed up any of the math, sorry, but the slip-up is still true).
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Contributed By:
Wesley Willis on 01-20-2002
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madted writes:
What "Kymaera" wrote makes no sense. "Cameronator" has got it (almost) right. The correct term Grissom should have used would have been acceleration due to gravity. Acceleration has units of m/s², whereas velocity has units of m/s. Acceleration due to gravity is about 9.8 m/s² and it's the rate at which objects accelerate when they are in free fall. However, the velocity of falling objects is reduced by air resistance, which usually depends on the speed of the object, so eventually the falling object will reach a speed at which the air resistance is equal to the force of gravity. At that point the object will not accelerate anymore, but will fall at a constant speed. That is what's referred to as terminal velocity. The only thing "cameronator" was wrong about is that gravity is a force, not an acceleration. As for what "Djouroboros" said: Yes it's only a television program, but this is high school physics. A person like Grissom, who's a walking encyclopedia, would surely know this.
3 of 3 people found this comment helpful. Did you? Yes
lineswine writes:
As a skydiver, I can POSITIVELY confirm that acceleration is 9.8 m/s/s until reaching terminal velocity - about 54 m/s (reached in 12 seconds or so). Therefore I agree 100% with cameronator: Kymaera is a retard.
2 of 2 people found this comment helpful. Did you? Yes
cameronator writes:
Kymaera is a retard. FACT. Velocity and acceleration are not the same thing. FACT. Terminal velocity is a velocity. FACT. 9.8 m/s/s is gravity. FACT. Gravity is an acceleration. FACT. Terminal velocity implies a constant maximum velocity so there is no acceleration (or 0 m/s/s).
1 of 3 people found this comment helpful. Did you? Yes
Djouroboros writes:
Because it's just a television program, and although you've spotted one mistake in hundreds of theories, i think they've done quite well to make an excellent series with tons of facts. you can't fault them for that.
3 of 18 people found this comment helpful. Did you? Yes
Kymaera writes:
There are two kinds of velocity, initial and terminal. A falling body's initial velocity would be zero and its terminal velocity would in fact be around 9.8 m/s^2, give or take a little given the body fell parallel or perpendicular to the ground (room for air resistance).
3 of 18 people found this comment helpful. Did you? Yes

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