Forces in Static Situations/Lesson Document: Difference between revisions

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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]]

Revision as of 08:53, 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: File:FFS1


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. File: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. 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: File:FSS3

Where do forces act? File: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.

File:FSS5 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. File:FSS6

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