Determine the mass of the object to be moved by placing it on the spring scales. For example, assume you have a 5-gram weight.
Attach the force gauge to the object and pull it along the surface, noting the measurement on the gauge. Assume a reading of 5 newtons.
Time it over a given distance to determine velocity; velocity equals distance divided by time traveled. Assume that you have a velocity of 0.5 meters per second.
Multiply the mass of the object by its velocity: 0.5 meters per second * 5 grams = 2.5. This gives you the momentum of the object: 2.5 newtons, per Newton's law of acceleration.
Subtract the momentum of the object from the original applied force. Per Newton's third law, the law of reaction, you can assume that total force in the system is equal. Because the object has a forward momentum of 2.5 newtons and you applied 10 newtons of force, the other 7.5 newtons is the frictional force.