*Forces:*

**Push or Pull is called a force **

* A force is a push or a pull which can
affect the motion of an object by changing its speed or direction. If two equal
and opposite forces act on an object it may be squashed or stretched. Both the
magnitude and direction of force acting on an object must be stated, because
both affect the way in which the object moves. If the direction in which a
force is acting is known, it is possible to predict the way the object it
affects may move. Forces are represented by arrowed lines whose length
corresponds to the magnitude of the force. The arrow indicates the direction in
which it is acting. Force is measured in Newtons (N).*
*
*
*Magnetic and Electrical Forces:*

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*
*
*Magnets can exert a force of attraction and repulsion*

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*

*There
are two types of forces which act at a distance: magnetic and electrical
forces. Objects which extra a magnetic or an electrical force can attract or
repel objects which are brought near them. The region in which the forces act
is called a field. The magnitude of the forces depends on the distance between
the objects. The closer they are together, the stronger the forces they exist.** *
*Frictional Forces:*

** Friction between the tyres and the road**

* Friction
is the force which resists the motion of two materials rubbing together.
Sometimes it is useful force – for example, it enables us to grip the ground as
we walk. A vehicle is able to grip the road due to the friction between its
tyres and the road surface. But friction also has unwanted effects. The
friction between the moving parts of a machine produces heat which wastes
energy. The friction between a cyclist and the air resist his or her forward
movement.*

*
*

*Gravitation and Weight:*

*
*

* Gravitation
is another force which acts at a distance. It is the force which exists between
any two masses, attracting them towards each other. Usually it is a weak force,
but if one object is massive, such as a planet, the force becomes noticeable.
Gravitational force depends on the distance between objects. The closer the
objects are together, the stronger the force they exert on each other.*

* Weight
is a measure of a planet’s gravitational pull on an object. Like all forces, it
is measured in Newton’s (N). The weight of an object depends on its distance
from a planet and the planet’s mass. On the Earth’s surface, the force of
gravity acting on a mass of 1 Kg is approximately 9.8 N. The magnitude of the
force diminishes as the mass moves further away from the Earth’s surface. An
object’s mass, however, remains the same wherever it.*

*Elasticity:*

**Force is Proportional to Elastic **

**Graph between Force and Extension**

**
**

*When
a force is applied to an object which cannot move, the object stretches. Its
molecules are pulled slightly apart and it becomes distorted. If the object
remains distorted when the force is removed, its distortion is called plastic.
If its molecules return to their original position, the distortion is called
elastic. Elasticity is, therefore, a material’s ability to return to its
original shape. To study the elasticity of a material, such as a strip of
copper, rubber or nylon, weights of increasing size are suspended from the
material. The amount by which the material is stretched is found by subtracting
its original length from its extended length. The size of the force is then
increased and the results are used to make a graph.*

*Hooke’s Law:*

* Hooke’s
law states that the extension of a material is proportional to the force which
is stretching it.*

* There
is a point, however, beyond which Hooke’s law is no longer obeyed. This is
called the limit of proportionality. If the substance is stretched further than
this point, it reaches its elastic limit. The substance stops being elastic and
remains distorted even when the stretching force is removed.*

* Provided
a material’s elastic limit is not exceeded, the principle of Hooke’s law can be
used in calculations to determine an unknown force or extension.*

* For
example, if a force of 10N stretches a spring by 60mm, the force which would
produce an extension of 42mm is calculated as follows:*

*60mm extension produced by 10N*

*1mm extension is produced by 10/60*

* Therefore, the force which would
produce a 42mm extension is calculated as follows: 10X42/60 = 7N*

*The
easiest way of measuring forces is to use a spring balance, after called a
Newton Balance. This is a device containing a spring. The spring obeys Hooke’s
Law. This means that it stretches in direct proportion to the force applied to
it. For example, if the forces applied to the spring are doubled, its extension
doubles. The spring balance will measure forces accurately until it is
stretched beyond its elasticity limit and it becomes permanently distorted.*

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*

*Scalar and Vector Quantities:*

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*
*

*
*
* Quantities
in physics are described as either scalar or vector quantities.*

*
**
*
* A
scalar quantity is one which has magnitude only. For example, Mass and
Temperature are scalar quantities.*

* A
vector quantity is one which has both direction and magnitude. Force is a
vector quantity. The magnitude and direction of a vector must always be stated.
Vectors can be represented with arrowed lines.*