Picture of Force Page |
FORCES:
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.
INERTIA:
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 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.
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.
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.
LAWS OF
FALLING BODIES:
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.
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.
Animation Showing Feather and Coin Experiment in Closed Glass Tube.
According
to the second and third law we determine two lower equation:-
v
--- =
K
t
(v =
velocity, t = time, K= constant)
h
--- = K
t|2
(h =
height, t = time, K = constant)
Hi Manash :)
ReplyDeleteWow, 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.
Regards
Jay
http://road-to-sanitarium.blogspot.in/