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So I have this project, where I make a shopping-cart-gokart and I would like to calculate how much force is needed for the shopping cart to start moving.

The biggest issue I had is that I could only calculate F = mg and then multiply it by the static friction coefficent, which resulted in the force I needed to overcome, but I believe that the resultant neccesary force should be smaller than the one I calculated, because the shopping cart has wheels.

I heard of something called the rolling friction, but I don't know any formulas that are connected with this idea.

In summary, I want to calculate the amount of Newtons required to start moving a shopping cart with wheels (taking them into account). BUT ALSO please explain what is rolling friction and how it works. Thanks in advance!

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  • $\begingroup$ The friction will be the friction resisting the wheels' rotation (such as the bearings) and not the friction arising from contact between the wheels and the ground. $\endgroup$
    – Vincent Thacker
    Commented Sep 13 at 18:25

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Rolling friction is difficult to find analytically and it best estimated empirically.

Build the cart and measure the force needed is the short answer.

If you want to estimate, you can focus on the two primary sources.

  • Tire rolling friction which depends on the geometry, materials, and inflation pressure
  • Shaft bearing rolling friction which depends on the geometry, materials, lubrication, and the type of bearing used.

Oh and do not forget if this cart is motored, then you need to add the motor rotational resistance, as well as any driveline friction introduced.

As I said, this is a very complicated calculation that requires an engineering degree, or just test the design.

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