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Unbalanced forces

In this module, we begin a study of the influence of unbalanced forces acting on bodies along with a study of the motion produced in bodies as a result ofunbalanced forces.

Statics versus dynamics

The earlier modules dealt with statics . We now begin a study of dynamics . The study of dynamics hinges largely on three important laws of motion, which werestated by Sir Issac Newton in 1686.

Making bodies move

We know from experience that we can cause small bodies to move by pulling or pushing them with our hands. In other words, we can cause a body to move by exerting a force onthe body. We also know that larger bodies can be caused to move by pulling or pushing them with a machine or with a beast of burden.

We are also familiar with the idea of falling bodies that move independently of someone pushing orpulling. We have come to know this as the result of the gravitational attraction between masses.

Aristotle's contribution, or lack thereof

I have never forgotten my physics professor, Brother Rudolph, at St. Mary's University in San Antonio, Texas, telling the class that Aristotle was ahindrance to science.

Aristotle taught that heavier bodies fall faster than lighter bodies, but he was wrong. It has been proven that all bodies fall towards the earth at the sameacceleration when the effects of air resistance are eliminated.

This is not too difficult to prove for yourself. A small piece of paper will fall to the ground much moreslowly than a coin when the paper is in its normal state. However, if the paper is crumpled into a very tight ball, greatly reducing the effect of air resistance, itwill fall to the ground almost as fast as the coin.

Galileo's contribution

Galileo and Newton clarified the ideas of motion through a series of experiments. For example, Galileo discovered the important relationship between force andacceleration. He concluded that in the absence of air resistance, freely falling objects have the same acceleration regardless of their differing weights.

Acceleration of gravity is constant

By rolling balls down inclined planes, Galileo discovered that the distance covered under a steady force is proportional to the square of the time ofdescent. By this, he concluded that acceleration is constant, at least near the surface of the earth.

Two cannon balls

The story goes that Galileo dropped two cannon balls of different weights off the Leaning Tower of Pisa and observed that they struck the ground below atexactly the same time. From this, he concluded that falling bodies are subject to the same acceleration regardless of their weight.


By rolling a ball down one inclined plane and up a facing incline plane, Galileo observed that the ball tended to rise to (almost) the original height on thesecond inclined plane. This was true even if the second incline plane was less steep than the first.

This suggested that if the second inclined plane were perfectly flat, the ball would roll forever trying to regain its original height. From this, Galileo issaid to have concluded that objects at rest tend to remain at rest, and objects in motion tend to remain in motion with the same velocity. (Recall that a changein direction is a change in velocity.)

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Accessible physics concepts for blind students. OpenStax CNX. Oct 02, 2015 Download for free at https://legacy.cnx.org/content/col11294/1.36
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