Concept of force and newton''s laws, Physics



1.   Ancient view objects tend to stop if they are in motion; force is needed to keep something motion. This was a natural thing to believe in because as we see objects stop moving after some time; frictionless motion is possible to see only in rather special situation such as in vacuum.


2.   Modern view objects tend to remain in their initial state; force is needed to change motion. Resistance to changes in the movement is called inertia. More inertia means it is difficult to make a body accelerate or decelerate.


3.   Newton's First Law states that an object will remain at rest or will move with constant the velocity unless acted upon by a net external force. (A non-accelerating reference frame is called an inertial frame; Newton's First Law deals with the inertial frames.)



4.   More is the force the more is acceleration:

1158_Newtons law.png

5.   The greater the mass of a body, the difficult it is to change its state of motion. Larger the mass means larger is the inertia. In other words, larger mass leads to less acceleration:

2144_Newtons law1.png

By combine both the above observations we conclude that:

2288_Newtons law2.png


6.   Newton's Second Law states that


2118_Newtons law3.png


                (or, we can also, write as F = ma).



7.   F = ma is one relation amongst three independent quantities (m, a, F ). For it to be useful, we must have separate methods by which we can measure mass, acceleration, and force. Acceleration is measured by observing the rate of change of velocity; mass is a measure of the amount of matter in a body (such as two identical cars have twice the mass of the single one). Forces (due to gravity, repulsion of two like charges,a stretched spring, etc).

8.  Force has dimensions of [mass] × [acceleration] = M L T -2 . In the MKS system the unit of force is the Newton. It has the symbol N where:

1 Newton  =  1 kilogram.metre/second2 .


9. Forces can be both internal and external. For instance the mutual attraction of atoms within the block of wood is known as internal forces. Anything pushing the wood is an external force. In the application of  F = ma, remember that F stands for the total external force upon the body.


10. Forces are the vectors, and so they must be added vectorally:


G      G      G      G

F = F1  + F2  + F3  + ⋅⋅⋅⋅ 


This means that the components in the xˆ direction should be added separately, those in the yˆ direction separately, etc.

11. The gravity acts directly on the mass of a body - this is a very essential experimental observation due to Newton and does not follow from F = ma. So the body of mass m1 experiences the force F1 = m1 g while the body of mass m2 experiences a force F2  = m2 g , where g is the acceleration with which anybody (may be big or small) falls under the influence of gravity.


13. Newton's Third Law: for every action there is an equal and opposite reaction. More precisely,

FAB  = −FBA , where FAB  is the force exerted by body B upon A whereas FBA is the force exerted by body A upon B. Ask yourself what would happen if this was not true. In that case, a system of two bodies, even if it is completely isolated from the surroundings, would have a net force acting upon it because the net force acting upon both bodies would be FAB  + FBA  ≠ 0.


 14. If the action and reaction are always equal to each other, then why does a body accelerate or goes in motion at all? Students are often confused by this phenomenon.  The answer: in considering the acceleration of a body you should consider only the (net) force acting upon that particular body. So, for instance, the earth pulls a stone towards it and causes it to accelerate because there is net force acting upon that stone. On the contrary, by the Third Law of Newton, the stone also pulls the earth towards it and this causes the earth to accelerate or moves towards the stone. Though, because the mass of the earth is so large, we are only able to see the acceleration of the stone and not that of the earth.

Posted Date: 7/26/2012 2:06:25 AM | Location : United States

Related Discussions:- Concept of force and newton''s laws, Assignment Help, Ask Question on Concept of force and newton''s laws, Get Answer, Expert's Help, Concept of force and newton''s laws Discussions

Write discussion on Concept of force and newton''s laws
Your posts are moderated
Related Questions
Inductors in dc circuits: If it is required to increases the value of inductance in a circuit, then two or more inductors may be connected in series.  The total inductance then

Define the term Mach-Zchnder Interferrometer. Mach-Zchnder Interferrometer The Mach-Zehnder interferometer is a device utilized to find out the phase shift caused through a

Older people wear eye glasses with bifocal corrective lenses . What is the eye defect that necessitate this eye glasses ?

The index of refraction of a particular medium is nearly the same for all wavelengths hence we often associate a single value the average value of the index of refraction to the me

A blackhole is a region of spacetime from which gravity prevents anything, including light, from escaping. The theory of general relativity predicts that a sufficiently compact mas

Q. The gain of an amplifier without feedback is 100 and the gain of an amplifier with feedback is 200. Calculate the feedback fraction. Solution : Voltage gain after feedba

The mass of a proton and of an antiproton is 1.00728 u. Recall that the conversion of exactly 1 u into energy yields 931.5 MeV. a. Measure the mass used up when a proton and

(i) A matter pulse is not electromagnetic in behavior. (ii) Practical observation of matter waves is possible only when the de-Broglie wavelength is of the order of the size of

Which is factual of the light from an actual physical object whose image is formed by a single thin lens? Ans: That's what light perform when it leaves a point on an objec