Why friction happens

The idea

Friction arises because even smooth-looking surfaces have many minute irregularities, which lock into each other when surfaces touch and oppose any effort to move one over the other.

A smooth table

A polished table looks smooth. Imagine looking at it through a very strong magnifying glass.

What do you think you would see?

• Tiny bumps and dents
• A perfectly flat surface
• Nothing at all

Zoom in

Press the button at the bottom each time, until the end.

Locked together

Even surfaces that look smooth have a large number of minute irregularities. When two surfaces touch, these irregularities lock into each other and oppose any effort to move one over the other.

Friction arises because of the minute irregularities in the two surfaces in contact. When the surfaces touch, the irregularities lock into each other and oppose any effort to move one surface over the other.

Notes

Friction arises due to the minute irregularities of the two surfaces in contact. They lock into each other and oppose any effort to move one over the other.

Check yourself

Why is there friction even between surfaces that look smooth?

When two surfaces are in contact, their irregularities …

The locked irregularities oppose …

Friction arises due to …

• Smooth surfaces are always sticky. No stickiness is needed. The minute irregularities lock into each other.
• They have minute irregularities that lock into each other — correct. Yes!
• Smooth surfaces are wet. Wetness is not the reason. The irregularities are.
• melt together. They lock into each other. They do not melt.
• move far apart. They lock into each other.
• lock into each other — correct. Yes!
• any effort to move one surface over the other — correct. Yes!
• any effort to make the surfaces look smooth. They oppose the effort to move one surface over the other.
• the weight of the surfaces. They oppose any effort to move one surface over the other.
• the colour of the surfaces. Colour does not cause friction. The irregularities do.
• the irregularities of the two surfaces in contact — correct. Yes!
• the shape of the sky. The sky has no part in it. The irregularities of the surfaces do.