The Physics
Factbook
An encyclopedia of scientific essays

Coefficients of Friction for Human Skin

search icon

Friction is a resistive force that opposes an object's motion or intended motion. The formula to compute the frictional force (f) is

f = µN

The coefficient ( µ) is unique for different materials. The normal force (N) is the countering force that the surface exerts on the object to oppose its weight.

We proceded as follows:

  1. Firmly attach the accelerometer to your wrist.
  2. Place an object on your wrist.
  3. Hit "Collect" in LoggerPro and gently raise your forearm up.
  4. Hit "Stop" when the object starts sliding.
  5. Determine and record the component of the acceleration due to gravity (a) parallel to your wrist at the instant that the object slips.
  6. Repeat steps 2–5 for four different materials.

equipment set up

After performing this experiment, we needed to compute the angle (θ) at which the object starts slipping. Since we know the acceleration components:

sin θ = a/g

After calculating the different critical angles, the coefficients µ can be calculated as follows:

N = mg cos θ
f = mg sin θ = µN = µmg cos θ
µ = tan θ

The data table below contains all our recordings and calculations.

Material Acceleration (m/s2) Critical Angle (°) Static Coefficient
Penny 6.27 39.77 0.83
Paper 6.41 40.85 0.87
Nickel 5.79 36.22 0.73
Plastic 6.86 44.43 0.98

Harvey Lei, Genna Ableman, Bridget Ritter, Africa Belgrave -- 2005

Students Choice
  1. Electricity & Magnetism
    1. The (dysfunctional) crystal radio
    2. The Kelvin water-drop electrostatic generator
    3. The two-way telegraph
    4. Magnetic field of a MetroCard
  2. Acceleration
    1. Acceleration of an elevator, hydraulic
    2. Acceleration perturbations of daily living
  3. Index of refraction of various household liquids
    1. glycerin, floor cleaner, degreaser, shower gel, baby wash
    2. vinegar, honey, floor cleaner, throat medicine, foot wash
  4. Coefficients of Friction
    1. Coefficients of friction for aluminum
    2. Coefficients of friction for glass
    3. Coefficients of friction for granite
    4. Coefficients of friction for paper
    5. Coefficients of friction for rubber
    6. Coefficients of friction for human skin
    7. Coefficients of friction for steel
    8. Coefficients of friction for wood