For procedures, see your mechanical laboratory manual.

Title: Rolling Friction

Aim

(a) To determine the coefficient of sliding friction between the mild steel wheels and different materials of the bars (specimen).
(b) To verify by experiment that;
(I) The square or the period of oscillation (t²) is proportional to the distance (L) between the wheel center.
(ii) Sliding friction is independent of the mass of the bar.
(c) To investigate the effect of changing the height (h) of the center of gravity.


THEORY

Rolling friction is the resistive force that slows down the motion of a rolling ball or wheel. It is also called rolling resistance.

When a force or torque is applied to a stationary wheel, there is a small static rolling friction force holding back the rolling motion. However, resistance from static sliding friction is what really causes the wheel to start rolling.

Once it is rolling, the resistance to the motion is typically a combination of several friction forces at the point of contact between the wheel and the ground or other surface. A simple version of the rolling friction equation is similar to the Standard Friction Equation.

When a force or torque is applied to a stationary wheel, there is a small static rolling friction that resists the rolling motion. However, it is too small to make much of a difference. Instead, static sliding friction prevents the wheel from simply sliding along the surface, resulting in the wheel rolling forward.

Rolling friction equation

The general equation for rolling friction is:
Fᵣ = μᵣN
where:
1. Fᵣ is the resistive force of rolling friction
2. μᵣ is the coefficient of rolling friction for the two surfaces (Greek letter "μ" sub r)
3. N is the normal force pushing the wheel to the surface

Applications

1. High‐speed trains
2. The lunar vehicle

References

1. Rolling friction and rolling resistance, Engineering Toolbox
2. Hibbeler, R.C. (2007). Engineering Mechanics: Statics & Dynamics
3. Rolling resistance, wikipedia.org