What is Coefficient of Friction?
By definition, coefficient of friction (COF) is the ratio between the force necessary to move one surface horizontally over another and the pressure between the two surfaces. In rigging, we commonly use COF to calculate how much force will be necessary to move a load based on the relationship between the object and the surface it’s moving across. It’s important to understand how to calculate friction force using the coefficient of friction and to consider it prior to selecting equipment to rig or move a load.
Below is a table outlining some of the common COFs used in rigging. While it varies per surface, typically, you will see that average coefficient of frictions fall between 0 and 1. The following calculations are not declared exact for all circumstances. However, they do represent the best rule of thumb and are reasonable and reliable for solving what force is necessary to move an object across a surface that is either flat, uphill, or downhill. Keep reading to see an example of how this is done.
How to Calculate Friction Force Using COF
Let’s say we are moving a load of material with a metal base plate across a level concrete floor. The load weighs 10,000 lbs. The above illustration tells us we would need to use the following formula:
COF x Weight of Load = Force
Looking at the table, we can see the COF for metal on concrete is 0.60. Now, let’s plug this information into the formula.
0.60 x 10,000 = 6,000 lbs of force required to move the load
Similarly, if we were moving the same load across a level concrete surface on a wooden base instead of metal, the force needed would drop since the COF of wood on concrete is lower than metal on concrete.
Here’s what the formula would look like with the wood on concrete COF (0.45) plugged in:
0.45 x 10,000 = 4,500 lbs of force required to move the load
Taking it a step further, if you placed the same load on machine skates on a level concrete surface, the required force would drop even more.
Looking at the table, we can see that the COF for a load on wheels is 0.05.
0.05 x 10,000 = 500 lbs of force required to move the load
As you can see, you can greatly reduce the force required to move a load just by putting it on wheels whenever possible. In effect, this allows for additional equipment options for handling the move.
For more information on friction force and the coefficient of friction or for help selecting the right rigging, pulling, or material handling equipment for your project, click to chat with a live rental support specialist or call 800-878-7305 today.