Download force and laws of motion

CHAPTER 9
FORCE AND LAWS OF MOTION
1) What is a force?
Force is a push or pull.
2) Give example for different forces in nature.
Gravitational Force, frictional force, nuclear force etc.
3) What are the effects of force?
1 .Force can move a stationary object or force can stop a moving object
2. Force can change the speed of a moving object.
3. Force can change the direction of a moving object.
4. Force can change the shape of an object.
4) Differentiate between balanced and unbalanced forces?
There are two types of forces namely balanced forces and unbalanced forces.
Sl.
Balanced Force
No
Unbalanced force
1
If the resultant of all forces acting on a
body is zero then the forces are
called balanced forces..When something
does not move the forces are balanced.
If net force on a body is non-zero it is
called unbalanced force.
Forces whose resultant is not equal to
zero are called unbalanced forces.
2
Example: An arm wrestling competition
Example: Gravity pulls a table down but among a strong person and a weak one.
that table is pushed up by the floor or the The resultant force will be in the
ground it stands on so doesn’t’ move.
direction of the force applied by the
strong person
5) Laws of motion
 Newton gave three laws of motion that describe the motion of bodies. These laws
are known as Newton's Laws of motion.


They describe the relationship between the forces acting on a body and its
motion due to those forces.
The three laws of motion were first compiled by Sir Isaac Newton in his work
Principia Mathematica, first published in 1687. Newton used these laws to
explain and investigate the motion of many physical objects and systems.
6) State Newton's First Law of motion
The first law of motion is stated as:
An object remains in a state of rest or of uniform motion in a straight line unless
compelled to change that state by an applied force.
7) Why Newton’s first law of motion is known as law of inertia?
All objects resist a change in their state of motion. The tendency of undisturbed
objects to stay at rest or to keep moving with the same velocity is called inertia.
Hence, the first law of motion is also known as the law of inertia.
8) What is the importance of first law of motion?
a. It gives the definition of force.
b.It gives the definition of inertia.
9) Define force.
Newton's first law of motion gives us a definition of force. It says that force is
something that changes or tends to change the state of rest or uniform motion of
a body
10) Define inertia
Inertia is the natural tendency of an object to resist a change in its state of rest
or of motion.
There are two types of inertia-inertia of rest and inertia of motion.
11) Why can dust be removed by shaking it, or beating it by a carpet?
Before the carpet was shaken, the dust was at rest. When the carpet was set in
motion, The
dust tends to remains at rest due to inertia. As a result dust got
removed from carpet.
12) Why do passengers in the bus tend to fall back when it starts suddenly?
When the bus accelerates from rest, the lower part of our body comes into
motion along with the bus while the upper part of body tends to remain at rest due to
inertia of motion and as a result which we fall backwards.
13) Why is it advised to tie a rope on the luggage while you travel by the bus?
Bus starts and stop suddenly during the journey and luggage can move because of
law of inertia
14) Why do passengers jumping out of a rapidly moving bus fall forward with his face
downwards, if he does not run forward?
The passenger’s upper portion will remain in motion due to inertia even on falling
on the ground and his lower portion will come to rest. So it will fall forward.
15) What is the use of seat belt in Cars?
1) if the car are stopped due to emergency braking ,then the driver and passengers
are no thrown forward so as to hit the steering wheel or wind screen
2)The slightly stretchable seat belts worn by the passengers increase the time taken
by the passengers to fall forward and thus less stopping force acts on them.
16) What is the relation between mass and inertia?
The mass of an object is a measure of its inertia. If mass more, inertia will be more
.If mass is less inertia will be less.
17) What do you mean by momentum?
The momentum, p of an object is defined as the product of its mass ,m and
velocity, v.
P=mv
Momentum is a vector quantity having direction same as velocity. S.I unit of momentum
is kilogram-metre per second (kgm/s).


We define the momentum at the start of the time interval is the initial
momentum and at the end of the time interval is the final momentum.
When the object moves then it gains momentum as the velocity increases.
Hence greater the velocity greater is the momentum
18) State Newton’s second law of motion.
The second law of motion states that the rate of change of momentum of an
object is proportional to the applied unbalanced force in the direction of the force.
19) Mathematical formulation of second law of motion.
Suppose an object of mass, m is moving along a straight line with an initial velocity, u. It
is uniformly accelerated to velocity, v in time, t by the application of a constant
force, F throughout the time, t.
The initial and final momentum of the object will be, p1 = mu and p2 = mv respectively.
Now change in momentum would be
Now force applied is proportional to rate of change of momentum. So,
where, a =(v-u)/t is the acceleration which is the rate of change of velocity. The quantity,
k is a constant of proportionality
The unit of force is chosen in such a way that the value of the constant, k becomes
one.For this, one unit of force is defined as the amount that produces an acceleration of
1 ms-2 in an object of 1 kg mass. That is,
1 unit of force = k × (1 kg) × (1 m s-2). Thus, the value of k becomes 1.
From Eq. 2
F = ma
(3)
20) What is the importance of second law of motion?
The second law of motion gives us a method to measure the force acting on an object
as a product of its mass and acceleration