Final answer:
Road surfaces are the most slippery during the first few minutes of rainfall. More friction is desirable when walking on slippery surfaces.
Step-by-step explanation:
The most slippery road surfaces occur during the first few minutes of rainfall. When rainwater first mixes with surface dirt and oil, it creates a slick layer on top of the road, causing decreased traction and making it slippery for vehicles.
Another example where more friction is desirable is when walking on a slippery surface. When there is more friction between the surface and our shoes or boots, it helps us maintain stability and prevents us from slipping and falling.