Law of Motion
You have often observed the table placed in your classroom . It always remains at the same place until you apply some force to move it. Like a book placed on the table remains at its place unless someone picks it back.
Similarly,
a satellite in the space continuously moves with constant speed because there is no air or
force of friction in the space.
examples,
a ball rolling on the
ground however stops after some time because friction
of ground and air resistance exert force on it and change
its state of motion or direction of motion. We can define
as
Newton’s first law of motion
A body continues its state of rest or of uniform
motion in a straight line unless an external force acts on
it.
The Newton's first law is also called law of inertia.
You may have sometimes observed that you putyour bag on the seat next to you. Whenever the bus stops suddenly, the bag slides forward off the seat. Whydoes it happen?
The bag was initially moving forward because it was on a moving bus. When the bus stopped, the bag
continued moving forward, which was its initial state of motion, and therefore it slid forward off the seat.
Inertia:
Inertia is the property of an object due to which it tends to continue its state of rest or motion. Inertia is resistance to change the state.
When a bus starts moving the passengers feel a backward jerk, because their lower part of body moves along the motion of bus but the upper part of the body tends to stay at its initial position of rest. On the other hand when you stop paddling your bicycle it does not stop at once. The bicycle continues moving. However the road's friction and air resistance act against its motion and bring it to rest after some
time.
Second Law of Motion
Find few marbles of different size.
⦁ Select one marble of very small size and another one larger about double the mass of first marble. Predict that by hitting with same force which marble will be accelerated . Now try hitting the marbles one by one with third marble with same force.
You may observe that the smaller marble catches almost double the acceleration as compared to bigger marble.
⦁ Can you explain this phenomena?
Newton's second law of motion describes the relation between force and acceleration.
Newton's second law of motion states that;
”when a net force acts on a body it produces
acceleration in the direction of force. The acceleration
is directly proportional to force and inversely
proportional to mass of body
Newton’s Third Law of Motion
This law describes what happens when a body exerts a force on another body. Many times you through a ball towards wall and it bounces back. If it is thrown with greater force the ball is returned back with greater push. It is because the wall reacts against the action of ball. While walking on ground you push the ground with feet the ground pushes you back thus you move .As these forces always occur in pairs, so
when one body pushes against another, the second body pushes back just as hard.
For example, when you put a book on table the book pushes the table downward, the table pushes back the book upward Thus Newton’s third law of motion can be defined as:
Newton’s Third Law of Motion
To every action, there is an equal and opposite reaction.
The action and reaction are forces that occur
together as a pair. They are always equal in quantity but
opposite in direction.
⦁ While standing on ground the gravity pulls you down against the ground, the ground pushes up against your feet.
⦁ When a rocket ignites its fuel behind it, the expanding exhaust gas pushes on the rocket causing it to accelerate
