# SCC Education

## Friction notes with example solved

Friction
Friction is a force that always exists between any two surfaces in contact with each other.
● There is no such thing as a perfectly frictionless environment.
● Even in deep space, bits of micrometeorites will hit a moving object, causing some friction
(although it is incredibly small).There are two kinds of friction, based on how the two surfaces are moving relative to each other:
1. Static friction
The friction that exists between two surfaces that are not moving relative to each other.
2. Kinetic friction
The friction that exists between two surfaces that are moving relative to each other.
In any situation, the static friction is greater than the kinetic friction.
● Have you ever tried to push a really big object? Did you notice that you were pushing harder,
and harder, and HARDER, until suddenly it was like glue that was holding it to the floor
snapped? Then, it felt easier to push the object than it did just to get it started.
● When it was still, you were trying to overcome the static friction (bigger force).
● When it finally started to move, you were now pushing against the kinetic friction
(smaller force).
Nobody is exactly sure why friction acts the way it does…
● Some physicists’ theories on friction involve the idea of the minute (tiny) imperfections in the
surfaces grinding against each other.
● Imagine two pieces of sandpaper rubbing past each other… they’d have a difficult time!
● Now remember that any surface, no matter how smooth it might appear to the naked
eye, has tiny bumps.
● These bumps on any surface will grind past other bumps on the other surface and cause friction.
● There is also the hypothesis that there are small electrostatic attractions between atoms of the
two surfaces, pulling on each other.
● Think of the electrons in one of the surfaces being attracted to the protons in the other surface.
● As you hold one object against another, billions of these attractions between the
electrons and protons of the two objects cause them to stick to each other somewhat.
● This pulling on each other could also be a source of friction.

Did You Know?
One of the problems that NASA would need to solve before sending astronauts on a long journey (like Mars) is protection from the microdust and micrometeorites in space. One of the most serious
problems is that as the spacecraft travels through space at high speeds, the front will be damaged the
most. Most plans have some kind of ablative shield that would cover the front of the craft. Ablative is
just a what you call any material that you expect to wear away because of some form of damage,while it protects whatever is underneath.

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