Force of Friction Calculator
Use this friction calculator to calculate the friction force between an object and the ground. It is based on a simple principle: friction is proportional to the normal force acting between the object and the ground. You can use this tool as a coefficient of friction calculator, too.
Force of Friction Equation
The formula that lets you calculate the friction force is very simple:
F = μ × N
where:
- F – Force of friction, measured in Newtons (N) or pound-force (lbf);
- μ – Dimensionless coefficient of friction; and
- N – Normal force (perpendicular to the ground surface), expressed in Newtons (N) or lbf.
How to Find Force of Friction
- Choose the normal force acting between the object and the ground. Let's assume a normal force of 250 N.
- Determine the friction coefficient. We can choose a coefficient of friction equal to 0.13.
- Multiply these values by each other: 250 N × 0.13 = 32.5 N.
- You just found the force of friction!
Static Friction vs Kinetic Friction
Static friction acts when the object remains stationary. Imagine you try to pull a heavy box. If we don't take friction into account, even the smallest force should cause some acceleration of the box, according to Newton's second law. In reality, you need to pull quite hard for the box to start moving because of the static friction force.
Kinetic friction (also called dynamic friction) acts on a moving object or, in other words, on an object with nonzero kinetic energy. If there were no kinetic friction, any object that you nudge (for example, a toy car) would never stop moving, as, according to Newton's first law, no force would act on it, so it would keep on going with a constant velocity.
Even though the formula is the same for static and kinetic friction, you need to remember that the coefficients of friction are different. The coefficient of kinetic friction is usually lower than the one of static friction.
FAQs
How do you measure the coefficient of friction?
There are two easy methods of estimating the coefficient of friction: by measuring the angle of movement and using a force gauge. The coefficient of friction is equal to tan(θ), where θ is the angle from the horizontal where an object placed on top of another starts to move. For a flat surface, you can pull an object across the surface with a force meter attached. Divide the Newtons required to move the object by the object's weight to get the coefficient of friction.
What would happen in a world without friction?
If there were no friction, there would be no anything. The friction that holds atoms together would disappear, so nothing would be able to form. Life wouldn't exist, as atoms wouldn't be near each other long enough to form simple molecules. The world would become a dangerous place to live, as cars in motion would lose the ability to stop. Good thing this scenario is physically impossible!
What is the unit of friction force?
The unit of friction force is the same as any other force — Newton (N) in the SI system, or pound-force (lbf) in the US customary system. Since μ is dimensionless, the friction force has the same units as the normal force.
Is static friction always greater than kinetic friction?
In most real-world scenarios, yes. The static friction coefficient (μₛ) is typically higher than the kinetic friction coefficient (μₖ). This is why it takes more force to get an object moving than to keep it moving.