Forces - An introduction

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Scalar and Vector Quantities

A scalar quantity has magnitude only 

A vector quantity has magnitude and direction

Arrows can be used to represent vector quantities

-the length of the arrow shows the magnitude

-the arrow points in the direction that the vector quantity is acting

Forces are vector quantities

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Contact and Non-contact forces

A force occurs when two or more objects interact. They are either:

Contact forces - the objects are actually touching 

E.g the tension as two people pull against one another

Non-contact forces - the objects are not touching

E.g the force of gravity acts even when the objects are not touching

Contact forces: friction, air resistance, tension, normal contact force, upthrust

Non-contact forces: gravitational force, electrostatic force, magnetic force

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Gravity

Gravity is a force of attraction between all masses

The force of gravity close to the Earth is due to the gravitational field around the planet

The mass of an object is related to the amount of matter it contains and is constant

Weight is the force acting on an object due to gravity

The weight of an object depends on the gravitational field strength where the object is and is directly proportional to its mass

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Resultant Forces

When more than one force acts on an object, these forces can be seen as a single force that has the same effect as all the forces acting together

This is called the resultant force

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Vector Diagrams

A free body diagram can be used to show different forces acting on an object

Scale vector diagrams are used to illustrate the overall effect when more than one force acts on an object

REVISE HOW TO DRAW VECTOR DIAGRAMS PAGE 9

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