2. Three fundamental quantities:
Mass : The quantity of matter is the measure of the same arising from it’s
density and bulk conjointly.
On Earth the terms mass and weight are often used interchangeably, but
in astronomy and Newtonian physics the mass of an object is related to how
much matter it contains. The mass of an object can be characterised by its
ability to resist a given force.
Motion : The quantity of motion is the measure of the same arising from the
velocity and quantity of matter conjointly.
3. Cont.…
Force (Definition 1): An innate forces of matter, is a
power of resisting, by which every body, as much as in it
lies, continues in its present state, whether it be of rest,
or of moving uniformly forward in a right line.”
Force (Definition 2) : An impressed force is an action
exerted upon a body, in order to change its state, either
of rest, or of moving uniformly forward in a right line.
4. First Law of Motion/ Law of
inertia
Newton’s first law states that:
“A body at rest will remain at rest unless acted on by an external force”
and
“a body in motion will remain in motion unless acted on by an external force”.
In astronomical terms, this means that in space bodies continue in straight lines
unless a force external to the body acts on them, and stationary bodies do not
spontaneously start to move. “In motion” in this context actually means at
constant velocity, i.e. their speed and direction of their motion do not change with
time.
External forces at the macroscopic level can be gravitational forces or mechanical
forces due to collisions.
5. Examples
Shake up that bottle of ketchup! When you shake that bottle, you bring the
bottom down, then suddenly you stop. This is inertia and it’s the inertia which
causes the ketchup to come out of the bottle
A driver or passenger in a moving car who is not wearing a seat belt will be
thrown forward when the car suddenly stops because he remains in motion. A
fastened seat belt provides a restraining force on the passenger’s or driver’s
motion. Air bags are used in motor vehicles because they are able to reduce the
effect of the force experienced by a person during an accident. Air bags extend
the time required to stop the momentum of the driver and passenger. During a
collision, the motion of the driver and passenger carries them towards the
windshield
6. Second Law of Motion/ Law of
acceleration.
The force F acting on a body is the product of its mass m and acceleration a.
or
F=ma
where F and a are vector quantities.
If we set the force to zero we find the acceleration is zero which is why Newton’s
second law implies Newton’s first law, which states the principle more clearly.
In astronomy the motion of the stars and planets are well described by Newton’s
laws of motion combined with his Universal law of gravitation. Indeed Kepler’s laws
can be derived from Newton’s laws of motion and gravitation.
At relativistic speeds (i.e. where velocity approaches the speed of light) Einstein’s
theories must be used to accurately describe motion. In Newtonian physics the
speed at which gravity propagates is infinite, whereas in relativity it propagates at
the speed of light
7. Examples
The mass of a truck is much larger than that of a car, which means it
requires more power to accelerate to the same extent.
When, for example, a car is driven 100km on a highway for 65km, much less
petrol will certainly be used than if it had to be driven at the same speed for the
same distance in a truck
⋅ A person falling on a cemented floor gets injured, but a person falling on a
heap of sand does not get injured this is because in heap of sand there is lot of
space between the particles which on force reduces while cement
is hard and solid which doesn't have much space between its particles. thus in
the case of sand the impulse of force is less due to time duration of the activity
being higher than in cement case.
8. Third Law of Motion
Newton’s third law states that:
To every action there is an equal, but opposite, reaction.
This means that, for instance, if the Earth pulls on a comet due to gravity, the
comet also pulls on the Earth. By combining this principle with the
Newton’s second law of motion which discusses acceleration, it is possible to
accurately describe the motions of any two bodies that exert forces on each
other.
9. Examples
The motion of the air-filled balloon:
Take an air-filled balloon is set free, the air inside it rushes out and the balloon
moves forward. In this example, the action is by the balloon that pushes the air
out of it when set free. The reaction of the air which escapes out from the
balloon acts on the balloon forward. A rocket moves on the same principle.
When its fuel burns, hot gases escape out from its tail with very high speed.
The reaction of these gases on the rocket causes it to move opposite to the
gases rushing out of its tail.
When two people pull the opposite senses of the same rope, and it stays at the
same point, it is also observed that there is an action and a reaction. That is
why the game of the rope or the “push and pull” is perfectly suited as an
example of this law.
