Acquire the necessary data. You will need the weight of the object--i.e., the normal force--and the coefficient of friction, representing the amount of friction two surfaces will generate. An estimated coefficient of friction can be referenced in a physics manual.
Use this formula: Friction force equals the normal force multiplied by the coefficient of friction.
Plug in your data. As an example, say you referenced a coefficient of friction of 0.20 and a weight of 100 Newtons (N). A Newton is a metric unit of force, but you could also use pounds.
Friction force = 0.20 * 100 Newtons
Friction force = 20 Newtons
Acquire the necessary data. Again, you'll need the weight of the object, which represents the normal force. You'll also need to find the friction force, measurable at the exact moment the object starts to give.
Adjust the prior formula to solve for the coefficient of friction: The coefficient of friction equals the friction force divided by the normal force.
Plug in your values. Say the normal force is 100 Newtons and the friction force is 20 Newtons:
Coefficient of friction = 20 Newtons / 100 Newtons
Coefficient of friction = 0.20