Ground pressure is the
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...
exerted on the ground by the
tires or
tracks of a motorized vehicle, and is one measure of its potential mobility, especially over soft ground. It also applies to the feet of a walking person or
machine
A machine is a physical system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromol ...
. Pressure is measured in the SI unit of
pascals (Pa). Average ground pressure can be calculated using the standard formula for average pressure: ''P'' = ''F''/''A''. In an idealised case, i.e. a
static, uniform net force
normal to level ground, this is simply the object's
weight
In science and engineering, the weight of an object is a quantity associated with the gravitational force exerted on the object by other objects in its environment, although there is some variation and debate as to the exact definition.
Some sta ...
divided by contact area. The ground pressure of motorized vehicles is often compared with the ground pressure of a human
foot
The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...
, which can be 60 – 80 kPa while walking or as much as 13 MPa for a person in spike heels.
Increasing the size of the contact area on the ground (the ''footprint'') in relation to the weight decreases the unit ground pressure. Ground pressure of 14 kPa (2 psi) or less is recommended for fragile ecosystems like marshes. Decreasing the ground pressure increases the flotation, allowing easier passage of the body over soft terrain. This is exemplified by use of equipment such as
snowshoe
Snowshoes are specialized outdoor gear for walking over snow. Their large footprint spreads the user's weight out and allows them to travel largely on top of rather than through snow. Adjustable bindings attach them to appropriate winter footw ...
s.
Examples
''All examples are approximate, and will vary based on conditions''
Note:
The pressures for average human and horse are for standing still position. A walking human will exert more than double his standing pressure. A galloping horse will exert up to 3.5 MPa (500 psi). The ground pressure for a
pneumatic tire is roughly equal to its inflation pressure.
See also
*
Contact patch
*
Tire load sensitivity
Related reading
* Theory of Ground Vehicles
References
Automotive engineering
Physical quantities
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