Momentumous

Hurricane Sandy has projected wind speeds that heighten at about 90 mph. So lets say some poor fool decides to go to the beach with this wind but not much rain, and stands observing 1 meter away from where the sand begins. It's pretty plausible that 90 mph winds could get a grain of sand moving, but how dangerous is that grain of sand? Well, lets say it takes the whole meter for the sand to get up to speed, and its final velocity is 90 mph just before it hits you. This is a velocity of 40.0 m/s. Using the equation (v)^2=(vo)^2=2ax, you find an accelleration of 808.02 m/(s)^2. If the grain of sand has a mass of .00000067 kg (.67 mg), then the net force felt by the grain of sand is .00054 N. The average muzzle velocity of a gun is 120 mph, only 30 mph (13 meters/s) faster. However, not only would a bullet's force be spread over a larger surface area, resulting in a lower pressure, but the force wouldn't be constant, since it would be slowed if only slightly by resistance. Whats more, a bullet lodges itself within a human, and "dangerous" is a standard that's reached WELL before deadly. So is a grain of sand dangerous? The grain of sand would generate a pressure of around .0119 psi. Considering the human body can withstand up to 50 psi on sudden impact, I'd say the sand isn't going to do anything traumatic. It might sting, especially if it gets in your eyes or throat, but it's certainly no bullet.

So lets say you're feeling crazy and want to wear some heels. Now you're about 135 pounds, the average weight of a female. That's approximately 61.2 kg. Multiply that by the constant of our friend gravity, and your body exerts a force of about 600N. Granted, this is split up between two feet unless you've had a tragic incident lately, so your foot feels about 300N of force just from standing. So lets look at it in terms of pressure, psi, pounds per square inch...or rather kg per square inch. Pressure is equivalent to F/A. If you're shoe size is a women's 8-9, your foot is probably around 10x3 inches. We'll shave off a handful of inches with the assumption that your foot is not perfectly rectangular, so lets say the area feeling the force of your weight is 25 inches. This means on a normal day with good arch support and nice, flat shoes, each foot feels a pressure of 12 kg/in^2. That's about 23 psi. So now you think, hey, let's wear some six inch heels! These heels are tall enough to essentially mean you're constantly standing on your toes. We'll attribute a square inch and a half for your arch "support" and heel, just for kicks, and what's left holding the majority of the force is the front pad of your foot and toes. That's about 8 square inches by my measurements. But the force exerted on your now 9.5 in^2 surface area hasn't changed. The force exerted on this surface area is still 300 N, and this area is less than half of the original surface area. 300/(9.5) is 31 kg/in^2 or 68 psi. That's almost triple the pressure your foot normally feels. That's like a full grown grizzly bear stepping on your toe. 6 inch heels tonight? No thanks, I'll take my nike's.