Dealing with friction in machines

• Friction is the force that opposes all movement
• It is the resistance that one surface or object encounters when moving over another
• Work must be done to overcome friction resulting in wasted energy and reducing the efficiency of machines
• Friction results in input being lost as heat
• Friction varies directly in proportion to the weight of the moving parts
• This means that the greater the weight of the moving parts the greater the greater the friction
• Friction is not affected by the area of contact between the moving parts
• Friction is higher between rough surfaces than on smoother surfaces

Reducing friction

• Popular methods of reducing friction include:
• lubrication and
• rolling friction and ball bearings

Lubrication

Lubricating grease. Image credit skf.com

• This is when a lubricant is used to reduce friction between the two surface layers
• A lubricant is a long-chain hydrocarbon molecule which maintains a surface layer even under great pressure
• An example of a lubricant is grease
• When lubricated the two solid layers slide more easily over one another
• The surfaces are kept apart by a thin layer of lubricant
• Heat from a machine e.g. an engine can cause the engine to “seize” and stop working
• Different engines therefore have various oiling systems to ensure smooth running

Rolling friction and ball bearings

Roller bearing. Image credit bicycles.stackexchange.com

• When one body rolls over another the friction is much less than when they slide over each other
• The effort required to push a car is much less when its wheels are turning
• Compared to trying to push it when its wheels are locked (e.g. when the breaks are applied)
• Ball bearings and roller bearings are used to reduce friction in various moving parts
• Such as in engines and wheels

NB In reality both methods are used wherever possible for example grease is  applied to bearings

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