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Forces in Static Situations | ==Forces in Static Situations== | ||
What are forces? | '''What are forces?''' | ||
A force on an object is a push or a pull on that object. It is best to always talk about the forces acting on a particular object i.e. specify the object upon which the pushes or pulls are acting. | A force on an object is a push or a pull on that object. It is best to always talk about the forces acting on a particular object i.e. specify the object upon which the pushes or pulls are acting. | ||
A force can rise in two ways: | A force can rise in two ways: | ||
(a) Through contact with another object. Examples: | (a) Through contact with another object. Examples: | ||
[[image:FFS1]] | |||
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(b) ‘Mysterious’ forces | (b) ‘Mysterious’ forces | ||
These are non-contact forces that occur when objects interact gravitationally or magnetically. There are also ‘mysterious’ electrical no-contact forces. | These are non-contact forces that occur when objects interact gravitationally or magnetically. There are also ‘mysterious’ electrical no-contact forces. | ||
[[image:FFS2]] | |||
It is quite legitimate to refer to these ‘non-contact’ forces as ‘mysterious’, since even scientists find it difficult to explain how they arise. | It is quite legitimate to refer to these ‘non-contact’ forces as ‘mysterious’, since even scientists find it difficult to explain how they arise. | ||
The size (or strength) of the ‘mysterious’ non-contact forces decreases as the distance between the interacting objects increases. | The size (or strength) of the ‘mysterious’ non-contact forces decreases as the distance between the interacting objects increases. | ||
How do you describe a force? | "'How do you describe a force?"' | ||
A force is described in terms of two qualities: its size and its direction. Scientists often use an arrow to indicate the size and direction of a force: | A force is described in terms of two qualities: its size and its direction. Scientists often use an arrow to indicate the size and direction of a force: | ||
[[image:FSS3]] | |||
Where do forces act? | '''Where do forces act?''' | ||
[[image:FSS4]] | |||
The force of reaction acts over a whole surface of contact – it is usually drawn at the centre of the surface, slightly displaced from other ‘force arrows’ for clarity. The two surfaces are also drawn slightly apart for the same reason. | The force of reaction acts over a whole surface of contact – it is usually drawn at the centre of the surface, slightly displaced from other ‘force arrows’ for clarity. The two surfaces are also drawn slightly apart for the same reason. | ||
[[image:FSS5]] | |||
Balanced forces | '''Balanced forces''' | ||
A stationary object remains still because all the forces acting upon it are ‘balanced’, i.e. the effect of each force acting on a body is cancelled out by an equal and opposite force. When the forces on an object are balanced, a scientist would say there is no net force or no resultant force acting on it i.e. all the forces cancel each other out. | A stationary object remains still because all the forces acting upon it are ‘balanced’, i.e. the effect of each force acting on a body is cancelled out by an equal and opposite force. When the forces on an object are balanced, a scientist would say there is no net force or no resultant force acting on it i.e. all the forces cancel each other out. | ||
[[image:FSS6]] | |||
