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 ...

exerted on the ground by the

tires A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a Rim (wheel), wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide Traction (engineering), t ...

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 using 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 macromolecules ...

. Ground pressure is measured in

pascals The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI), and is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is defined ...

(Pa) which corresponds to the

United States customary units United States customary units form a system of measurement units commonly used in the United States and U.S. territories since being standardized and adopted in 1832. The United States customary system (USCS or USC) developed from English unit ...

unit of

pounds per square inch The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied t ...

(psi). Average ground pressure can be calculated using the standard formula for average

: ''P'' = ''F''/''A''. In an idealized case, i.e. a

static Static may refer to: Places *Static Nunatak, a nunatak in Antarctica United States * Static, Kentucky and Tennessee * Static Peak, a mountain in Wyoming ** Static Peak Divide, a mountain pass near the peak Science and technology Physics *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 the force acting on the object due to gravity. Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar quan ...

divided by contact area. The ground pressure of motorized vehicles is often compared to 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 a separate organ at the terminal part of the leg made ...

, 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 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 often observed in activities like

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 footwe ...

ing.

Examples

''All examples are approximate, and will vary based on conditions'' Note: The pressures for adult human male 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 A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a Rim (wheel), wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide Traction (engineering), t ...

is roughly equal to its inflation pressure.

References

Automotive engineering Physical quantities {{physics-stub

Examples

See also

Related reading

References