Examples of Friction

Whenever two objects move past each other, or relative to each other, and are in physical contact they produce the force of friction. Friction always acts in the opposite direction to the motion of the object concerned.

When two solid object move past each other in this way, the friction is caused by the microscope undulations in the surfaces that then catch on each other and slow the objects down. Even a smooth surface, like glass or ice, has microscope imperfections. The larger these are and the more of them that exist on an object the greater its potential to generate friction.

Friction, figure 1

is not only affected by the ‘roughness’ of the surfaces, but also by the relative speeds with which the objects areFriction moving.

The objects do not have to be solids for friction to occur, gasses, liquids and solids in contact with each other and in motion will generate a frictional force.

Friction is often given different names depending upon the situation and the nature of the objects concerned.

__Grip __is friction between two solid objects, often used in the context of tyres or shoes and their ability of grip hold of a surface and prevent skidding or slipping. High friction surfaces, often with specially designed patterns have high grip.

Air resistance refers to the friction between a moving object and the air it is ‘pushing’ out of the way as it moves. Cars are designed to reduce this form of friction, whereas a parachute is designed to maximise this air resistance to slow the fall.

__Drag __can be used to identify the friction of an object moving through either a liquid or a gas. More accurately it is the friction of objects moving in a fluid, (in science the word fluid is used to refer to both liquids and gasses). Most people experience drag when they swim, as the water has a much higher density than the air, as we swim we become aware of the additional drag making it harder to move through water than air.

Reducting Friction

In many situation friction is considered a problem as it results in energy being transferred into heat that is then dissipated into the surrounds, resulting in less efficient system. In an engine, for example, the frictional heat generated would be enough to melt parts of the engine and prevent it from working if the friction was not reduced to acceptable levels.

To reduce the potential for energy loss and damage to moving parts in many systems a lubricant is used to smooth out the microscopic undulations in the surfaces. This allows the objects to move more freely past each other, however, there will still always be some frictional heat loss. It is not possible to make a surface that is 100% friction free.

In many rotating systems, like the drive shafts on engines, ball bearings are used to provide a smoother surface and reduce friction, this is always accompanied by a lubricant such as an oil or grease.

Explain why friction occurs when a chain on a bike moves past a gear wheel.
Explanation: Both of the part will contain thousands of tiny, microscope undulation giving them a rough surface. As these move past each other they can catch on each other, slowing the movement down and causing heating of the chain and the gear wheel.
What is the difference between drag and grip?
Your answer should include: friction / between / two / 2 / solid objects
Explanation: Although they are both examples of friction, grip refers to the friction between two solid objects and is often a desirable form of friction as it prevents skidding and sliding during motion. Drag refers to the friction produced when a solid object moves through a fluid (gas or liquid).
Suggest how unwanted friction can be reduced in an engine.
Your answer should include: lubricants / lubricate
Explanation: Lubricants such as oil and grease,as well as ball bearings can be used in different parts of an engine to reduce unwanted friction.