FORCE

Force is defined as a push or pull on an object.

                                     A person pushes a car

The SI unit of force is newton (N).

Newton

Is the amount of   force which will cause a mass of 1kg to move with an acceleration of 1m/s².

Force = mass × acceleration, F=ma.

When   mass=1kg

 Acceleration=1m/s²

       F=1kg×1m/s² =1N.

What force can do?

ü Can cause the object to move

ü Can cause object to stop

ü  Can cause the change of shape and size of an object

ü Can cause the change  of  direction of an object

TYPES OF FORCES

1.     Fundamental forces

2.     Non fundamental force

The force can be action in contact force or action at distance force.

ACTION IN CONTACT

In action in contact there is physical contact between the force and the point of application of force. Examples of action in contact forces are driving a nail into a wood by hammer (impact), kicking the ball, Tension force, elastic force, friction force and air resistance.

ACTION AT DISTANCE FORCE

In action at distance there is no physical contact between the force and the point of application of a force and yet a force can cause effect on the point of application i.e.  it can pull or push object. Examples of action at distance forces are gravitational force and electromagnetic force.

FUNDAMENTAL FORCES

There are four fundamental forces; these are called fundamental forces because they are the basic forces occur in nature.

       I.            Gravitational force

    II.            Electric force

 III.            Strong nuclear force

IV.            Weak nuclear force

GRAVITATIONAL FORCE

This force is equal to the weight of an object; the earth and other planet pull the objects towards themselves by the force of gravity. To find the weight of an object we find the force an object exerts on anything which is freely supporting it.

Since the weight is equal to gravitational force it is common to refer gravitational force of the earth on an object as the weight of an object so it is also obvious to say weight of an object is the force of attraction of the earth on an object towards its center.

In fact the earth pulls the object by its gravity and in turn the object exerts a force on something which supports it and the force is what is referred as weight.

Value of gravitational field strength on the earth

Gravitational field strength is a force per unit mass on an object, on earth the gravitation field strength is 9.8N per kilogram (9.8N/Kg). This is also called acceleration due to gravity or acceleration of the free fall and it is given as 9.8m/s².

1kg     = 9.8N

Mass  ? =F

 By crossing multiplication of the above, the relation will be

F=Mass×9.8, since 9.8 is symbolized by ‘g’ and mass by m then F=mg.

From   F=mass × acceleration (F=ma)

Then g=a. therefore gravitational field strength can be expressed as force per unit mass or as acceleration.

 Properties of gravitational force

ü It is always attractive (always pulling objects and never repels)

ü It is the weakest force compared to other fundamental forces

ü It is central force( it acts between center of masses

ü It operates over long distance.

ELECTROMAGNETIC FORCE

This is both magnetic and electric, it stronger than gravitation force.  Example   of the   electromagnetic   forces   is

       I.            Force in formation   of   molecule of a substance, Atoms attracts each other by the electromagnetic forces and combine to form molecule.

Example hydrogen atoms combine with oxygen to form a molecule of

Water.

    II.            Force existing between two parallel wires carrying current placed a certain distance apart.

                          

       I.            Force between two charged particles.

Properties of electromagnetic force are

ü It can be attractive or repulsive

ü It is stronger than the force of gravity

ü It is central force

ü It operates over long distance.

STRONG NUCLEAR FORCE

Is the force which binds together the proton and the neutron in atomic nucleus.

Energy is released in nuclear fission and nuclear fusion. Nuclear fission is the reaction in which an atomic nucleus of a radioactive element splits by bombardment from an external source and nuclear fusion is the fusing together of lighter atomic nuclei to form heavier one.

Both processes release strong nuclear energy. 

                                       Nuclear fusion            

             

                 

Properties of strong nuclear   force.

ü It is an attractive force

ü It is operates in very short distance.

ü  Non central force, it acts within the atomic nucleus.

ü It is stronger than gravitation force.

WEAK NUCLEAR FORCE

Is the force which occurs in some nuclear processes example radioactive decay and nuclear fusion of subatomic particles

Radioactive material emits gamma ray, beta particle     and alpha particle

Properties   of weak nuclear force.

ü It is stronger than gravitational force but weaker than  electromagnetic force

ü It is act in very short distances.

ü It is weaker than strong nuclear force

EFFECTS OF FORCES

ü Stretching

This is the increase in length of an object when a force is applied, example pulling a rubber band or spiral spring, the force responsible for this change is called stretching force

                                              stretching a spiral spring

ü Compression

This is decrease in volume or size of an object when a force is applied on it. Example squeezing a spongy, compressing a gas in piston, and compressing a spiral spring. The force which cause compression is called compressional force

                           

                                           Compressing a spiral spring

ü Restoring

Elastic materials when are stretched, compressed or twisted can return into their original shape and size when the force is removed, this is called restoring. The force which cause material to retain its original shape and size is called restoring force

Spring has returned to its original shape after  stretching or compression force removed

ü Torsion

This is twisting   of   object   by applying a force to one end while the other is held firm or twisted in the opposite direction. The force which causes twisting is called torsional force

                              Twisting a ruler

ü Attraction

Attraction is a pull without physical contact example of attraction is gravitation attraction, attraction on unlike charged particles and magnetic attraction. The force which cause objects to be attracted is called attraction force

ü Repulsion

      A force that tends to push two objects further apart, example force on like electric charges or like magnetic poles.

The force responsible for repulsion is called repulsion force

                               Repulsion on like charged particles

                                                                                               

ü Friction

This is opposition to motion, the force which opposes motion is called friction force, it occurs between two surfaces moving relative to one another.

Advantages of friction force

ü It enables us to walk

ü It enables  objects to stop.eg car,bycicle and motor bike 

ü It enables us to start fire

Disadvantages of friction force

ü It causes wear and tear of machinery parts

ü It produces undesired heat on machinery parts

ü It produces noise

QUESTIONS

1.     Define the term force.

2.     What are types of force

3.     Name the four basic interactions of nature.

4.     Illustrate any two effects of force you know.

5.     Give two examples of action at distance force

6.     Is compressional force action in contact force?

7.     List five advantages of friction force