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Coefficient of Friction

Slip and fall accidents are a leading cause of injury and fatality in the United States. A large number of slip and fall accidents are due to slipping, usually on slippery surfaces. When a person walks, they exert a downward force. They also exert a “horizontal force” in order to propel themselves forward. The backward horizontal force is resisted by friction between the shoe and the surface on which they are walking. When there is insufficient friction to resist this force, a person will slip.


When a person sues for compensation for a slip and fall injury, the slipperiness of the surface at issue becomes a central issue for the court. The slipperiness is universally measured by a dimensionless ration called the coefficient of friction, or COF. The higher the value of the COF, the less slippery the surface is. The smaller the value of the COF, the more slippery it is. This number is sometimes referred to as “the friction factor.”

The COF is a scientific numerical measurement; assessed by an instrument such as the Binary Output Tribometer (BOT), also called a slip-tester or tribometer. This high-tech instrument measures the slip resistance of a surface. These instruments vary in complexity from a simple metal block, to complicated pendulum instruments with parts that are jump started by a trigger mechanism. Regardless of the complexity of the device, they all operate in a similar fashion. Each serves to simulate the motion of the bottom of a shoe or bare foot, and measure the slip risk of the surface.

The conditions during testing should mimic the conditions at the time of the accident—for example, wet, contaminated, icy, or dry.

The Types of COF Conditions

There are two types of COF conditions: static COF and dynamic COF. The former is traditionally measured by placing a metal block on a clean level surface. The static COF is determined by dividing the measured force by the weight of the block. The dynamic COF is measured while the block is moving—when it is being pulled parallel to the surface.

Wet surfaces produce a lower COF, as they are more dangerous than dry surfaces. Water is the most common contaminant and can wet a surface in varying degrees. The more wet a surface is, the more dangerous it is, and a person’s foot can even hydroplane on a pool of water much like a car driving on a road covered with pooled water. This condition will usually yield a COF of 0.10 or less. The average range of COF is between 0 to about 1.1. In closing, a property owner is responsible to maintain their property and keep it free from hazards to avoid a premises liability lawsuit.

Chester County Slip and Fall Lawyers at McCann Dillon Jaffe & Lamb, LLC Pursue Maximum Compensation for Victims of Slip and Fall Accidents

If you or someone you love has been injured in a slip and fall accident, let us handle your legal concerns so that you can focus on your recovery. We can help you seek compensation for medical bills, lost wages, and pain and suffering. The experienced Chester County slip and fall lawyers at McCann Dillon Jaffe & Lamb, LLC are well versed in premises liability laws. Call us today at 215-569-8488, or contact us online for a free consultation.