Forces in Static Situations/Lesson Document: Difference between revisions
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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:<br /> | ||
[[image:FFS1.jpeg]] | [[image:FFS1.jpeg|800x1000px]] | ||
Note that, on perfectly level ground two motionless objects can lay side-by-side in contact but will not be exerting forces on each other. This is rather like placing two balls side-by-side in contact on a snooker table. | Note that, on perfectly level ground two motionless objects can lay side-by-side in contact but will not be exerting forces on each other. This is rather like placing two balls side-by-side in contact on a snooker table. | ||
(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.<br /> | ||
[[image:FFS2.jpeg]] | [[image:FFS2.jpeg|800x1000px]] | ||
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:<br /> | ||
[[image:FSS3.jpeg]] | [[image:FSS3.jpeg|800x1000px]] | ||
'''Where do forces act?''' | '''Where do forces act?'''<br /> | ||
[[image:FSS4]] | [[image:FSS4.jpeg|800x1000px]] | ||
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.<br /> | ||
[[image:FSS5.jpeg]] | [[image:FSS5.jpeg|800x1000px]] | ||
'''Balanced forces''' | '''Balanced forces'''<br /> | ||
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.<br /> | ||
[[image:FSS6.jpeg]] | [[image:FSS6.jpeg|800x1000px]] | ||
Latest revision as of 09:09, 4 October 2012
Forces in Static Situations
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 can rise in two ways:
(a) Through contact with another object. Examples:
Note that, on perfectly level ground two motionless objects can lay side-by-side in contact but will not be exerting forces on each other. This is rather like placing two balls side-by-side in contact on a snooker table.
(b) ‘Mysterious’ forces
These are non-contact forces that occur when objects interact gravitationally or magnetically. There are also ‘mysterious’ electrical no-contact forces.
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.
"'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:
Where do forces act?
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.
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.
