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My Pages On Different Subjects which Hyperlinked to all my Blog Posts

Tuesday, 29 May 2012

Newton`s Three Laws of Motion and Galileo`s Laws of Falling Bodies

Picture of Force Page


We know that objects that are not moving do not start moving by themselves.For example a football will not move unless it is kicked.Things that are at rest seem to want to stay there.

Balance a postcard on your fingertip with a coin on it. If you flick the postcard away quickly, the coin will stay on your finger. You may have seen a similar trick with a table full of plates. Some people can pull away the tablecloth so that the plates stay on the table. The plate do not want to move .It is better not to try this particular trick- it takes a lot of practice.

There are other examples of things wanting to stay in place.Look at people standing  in a bus. When the bus starts they tend  to fall backwards. This is because  they were stationary and their bodies want to stay like that. If the bus with a jerk everyone falls forward.There is nothing to stop them so they keep on moving .If someone runs into you.You can feel how their body does not want to stop moving.


Generally ,things do not want to move if they are at rest .Nor do they want to stop once they are moving.This tendency of something to stay at rest or stay moving is called inertia.An empty tea trolley has very little inertia.It is easy to get it moving and it is easy to stop it once it has started. When you load a trolley with heavy things its inertia is much greater. It is more difficult to start and stop because it has more mass.

To start and stop things you need to pull or pushes are known as forces. If you hold magnets close together you can feel them pull or push against  each other . This is an example of a force.

A force is needed to start a body moving and to slow down a moving body .In other words the force overcomes the inertia of the body.

Picture of Sir Isaac Newton

Sir Isaac Newton first law of motion:- gave an explanation of force, motion , and inertia. He said that an object will stay at rest unless it is acted on by force. He also said that if  an object is moving at a constant speed it will continue to do this unless it is acted on by a force.

Newton`s second law of motion:-   The rate of Change of the object`s momentum (mass * velocity) is directly proportional to the force acting upon it. The direction of change of momentum is also same of the direction of the force.
P = m*v (P = momentum, m = mass, v = velocity). 

Newton`s Second Law: In a Cricket match bowler throw the ball toward batman`s wicket,

In a Cricket match bowler throw the ball toward batman`s wicket, therefore bowler acting force on the ball, thus the momentum of the ball is proportional to bowler`s throwing force (ball speed or momentum increases with the bowler throwing force) .The direction of change of momentum of the ball is also same of the direction of the bowler throwing force (i.e. towards batman`s wicket). On the other hand when batsman hit the ball with its bat (i.e. acting force) the ball momentum change with the bat`s hitting force and ball direction also change towards boundary.

Newton`s third law of motion:-  Every action has it equal and opposite reaction. This is how rockets work. Hot gas is forced out of the back of the rocket.The equal force on the rocket (the reaction) pushes it forward.

A bullet fired from a gun

A bullet fired from a gun gradually slows down and falls  to the ground. This happens because air pushes against the bullet as it moves . In outer  space, where there is no air ,The bullet would continue moving.

                                                                                  Animation Showing Opposites Forces (Gas Force and Rocket Pushing Force) of Rocket.

This is how rockets work. Hot gas is forced out of the back of the rocket.The equal force on the rocket (the reaction) pushes it forward.

This is why a space ship outside the earth`s  atmosphere can move without fuel. Its rockets are only necessary to allow the ship to change velocity - that is , to slow down (decelerate) , to speed up (accelerate) or to change direction.Newton suggested that the bigger the force, the more the acceleration (or deceleration) produced.

Jet Engine

when a Cricket bat strikes a ball.

 You see something similar, although on a much smaller scale, when a Cricket bat strikes a ball. There's no doubt the bat applies a force to the ball: It accelerates rapidly after being struck. But the ball must also be applying a force to the Cricket bat. The mass of the ball, however, is small compared to the mass of the Cricket bat, which includes the batter attached to the end of it. Still, if you've ever seen a wooden Cricket bat break into pieces as it strikes a ball, then you've seen firsthand evidence of the ball's force. 

Balance a card with a coin on it on top of the glass

Balance a card with a coin on it on top of the glass. Ask some one to put the coin in the glass without touching either.The trick is to flick the card quickly so that coin drops into the glass.If you flick the card the coin does not move with it.This is because its inertia tries to keep it in the same place.

Metal ball on the Toy Car

                                                                                                          Animation showing Inertia Experiment 1) Glass and Coin 2) Ball and Toy Car.

If you Stand a metal ball on the toy car and push it on same velocity the ball become stand still on the toy car until the toy car face any obstruction. When the car  face sudden obstruction the car become stop but the ball take into motion due to its inertia of motion and fall on the ground from the toy car.  

Experiment of Two same Zinc Ball and Wooden Ball ,Zinc Ball respectively on two Toy Cars on Motion.

Inertia and mass of an object have same unit: In an experiment when we attach two Zinc ball (of same weight and size ,white ball in picture) two sides of a stick which is attached to stand on a toy car in a way they can move freely. Then we suddenly put the toy car into motion by push. At the time of push we check that two zinc ball must placed laterally with the direction of the toy car motion. We saw that two zinc-balls were remain still during and end of the motion.

After that we repeat the experiment by slight change , instead of taking two same zinc balls we now take one zinc ball and one wooden ball (of same size, Orange ball in picture) . Now the stick and the two balls on the toy car rotating when it on the motion. At start the wooden ball move front of the zinc ball and opposite occur when toy car stopped.

                                                                                                      Animation Showing Mass-Inertia Experiment.

On the first situation two zinc ball have same mass therefore zinc balls have same inertia . Therefore both ball have same inertia for resting and motion ,For that reason they become still.

On the second situation the zinc ball have more mass and inertia than wooden ball.  During toy car motion stage wooden ball have less resting inertia than zinc ball , therefore wooden ball move faster than zinc ball. During toy car stoppage stage wooden ball have less motion inertia than zinc ball, therefore zinc ball move faster than wooden ball.

Picture of Page on Laws of Falling Body

Objects falling towards the ground move faster and faster . This is because they are accelerated by the force of the gravity . People used to think that if two objects were dropped from the same height the heavier one would reach the ground first .
An Italian scientist called Galileo showed that this is not true .All objects fall at the same rate. He is supposed to have tested this by dropping stone from the leaning tower of Pisa - but this is probably only a myth. The heavier objects have bigger force pulling it to the ground .It also have more mass and therefore more inertia .So only it falls at the same rate as the lighter object. Galileo discovered three laws of falling bodies:-

Picture of Galileo

1) At the airless area all objects fall at the same rate.

2) At the certain time the velocity of an object directly proportional to its time.

3) At the certain time the distance which is covered by an object is directly proportional to the square of the time.


Coin Feather Experiment in Closed Glass Tube
Take a glass tube of length of 1 meter and circumference of 5 cm . Put one coin and a feather inside it and close its both openings with lid airtight. Now turn the glass tube upside down and you will see that the coin fall more quickly than feather.  Repeat the experiment after suck out all the air from the glass tube by air suction pump. Now you will see that both the feather and coin fall at same rate. This proves the first law of Galileo.

                                                                                                             Animation Showing Feather and Coin Experiment in Closed Glass Tube.
According to the second and third law we determine two lower equation:-

--- = K 

(v = velocity, t = time, K= constant)

---  = K

(h = height, t = time, K = constant)

1 comment:

  1. Hi Manash :)

    Wow, I must say, you've gone in-depth into this topic. Detailed explanations for the common public to understand and even the science-background people to refresh their memories.
    Thanks for sharing this post. :)

    Keep posting.





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