Question

Question #38469

Answer 1

The amount of surface area in contact with the ground is far less when the man is walking than when he is standing still.

Explanation:

If we calculate pressure as the the force exerted per unit area

`color(white)(aaaaaaaaaaaaaa)"Pressure"= ("Force")/("Area")`

and compare the pressure when walking (only the heel of 1 foot in contact, in this instance) vs. when standing still (both feet are in contact), taking the average weight of the man as `720" N"`, then

`color(white)(--)"Heel SA: 0.0064 m"^2 and "SA of both feet: 0.0258m"^2`

(source: http://hypertextbook.com/facts/2003/JackGreen.shtml)

`color(white)(aa)`

`color(blue)"when walking"rArr"P"= ("720 N")/("0.0064 m"^2)=112500 N/m^2`

`color(white)(--)"vs"`

`color(red)"when standing still"rArr"P"= ("720 N")/("0.0258 m"^2) = 27907 N/m^2`

we clearly see that the Pressure is `"4 x"` greater when the person walks as opposed to when he stands still on both legs.