Force and equilibrium: Frictional forces on mobility walkers

A mobility walker or “walker” is useful for people who are at risk of falling. This includes the elderly, individuals with severe knee arthritis, and patients recovering from accidents or invasive leg surgery. Instead of maintaining the typical upright position, a walker allows the person to transmit some of their body weight from their legs, through their arms, and onto the walker by leaning on it.

To reduce friction, people often place tennis balls on the bottom feet of the walker. Compared to the rubber grip originally attached to the walker, the tennis balls have a significantly lower coefficient of friction. This allows the walker to slide across the ground with much less applied force by the patient, making it further useful for those with additional weakness in the arms or upper torso.

The diagram depicts an example of a 2.0 kg mobility walker being slid across the floor due to an applied force of 20N directed at an angle of 60${}^{\circ }$‍. Assume the walker is sliding across the floor with constant velocity.

Figure 1. A 20N force applied to a walker with tennis balls attached to the bottom.