A block of wood is at rest on a wooden ramp. When wheels are attached to the block of wood, it moves down the ramp. Explain each situation in terms of friction.
The Correct Answer and Explanation is :
When a block of wood is at rest on a wooden ramp, the frictional force between the block and the ramp prevents the block from moving. This is because the static friction force between the surfaces resists any relative motion. Static friction adjusts its magnitude based on the applied force, up to a maximum value determined by the coefficient of static friction and the normal force (the weight of the block). If the ramp’s incline is shallow or the block is not given enough initial force to overcome the maximum static friction, the block will remain stationary.
In the second scenario, when wheels are attached to the block, the situation changes because the type of friction acting on the block also changes. Instead of static friction, rolling friction comes into play. Rolling friction is much weaker than static friction. This is due to the fact that when a wheel rolls, there is less surface contact between the wheel and the ramp compared to when the block slides. The wheel does not slip or drag along the surface, but rolls over it, which reduces the energy lost to friction. As a result, the block with wheels will move down the ramp more easily than the block without wheels.
Friction between the block and the ramp acts as a resisting force when the block is stationary, preventing it from sliding. However, once wheels are added, the type of friction changes to rolling friction, which is much smaller and allows the block to move more freely. The reduction in friction makes it easier for the block to move under the influence of gravity, causing it to roll down the ramp instead of remaining stationary.