Chapter 2: Force....Notes
Anandita will be uploading my Physics notes from Ch 2 here. Subsequently, we will discuss here as revision for SA1
Nikhil
Chapter 2: Force....Notes
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» Manava Bharati School, New Delhi-Class IX / Physics Classroom lessons
» Chapter 2: Force....Notes
Summary:
Volunteer - Anandita Dalal
Balanced Force
If the resultant of all the forces is zero, the forces are called balanced forces.Eg: Two springs X and Y are tied to the two opposite forces of a block. If we apply a force by pulling the string X, the block will move to the right. Simarly if we pull the string Y, the block will move towards the left side. bu if the block is pulled from both the sides with equal forces, the block will not move.
Unbalanced Forces
If the resulyant of all the forces acting on a body is not zero, the forces are called unbalanced forces.When unbalanced force act on a body, they produce a change in it's state of rest or of uniform motion. that is unbalanced forces can move a stationary body or they can stop a moving body.
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An object at rest or in uniform motion will remain at rest or in uniform motion unless an unbalanced force act upon it.
In other words, all objects resist a chnge in their stateof motion. in a qualitiative way, the tendensy of undisturbed objects to stay at rest or to keep moving with the same velocity is called inertia.
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Momentum: The total quantity of motion contained in a body is known as it's momentum.It is a vector quantity and is denoted by p.
Mathematical expression for momentum is
p = mv
Second Law Of Motion: Te rate of change of momentum of an object is propotiona to the applied unbalanced force in the direction of forcs.
Where p is momentum, 'm' is mass of the body and 'v' is the veloity of the body.
According to the third law of motion by newton we apply force whoch is devided propotional to the momentum.
The Concept Of Momentun
Momentum is a better quanyity that is define as the product of mass and velocity.
deravation of second law of motiom
F=applied force
p1=initial momentum
p2=final momentum
u=initial velocity
v=final velocity
t=time
m=mass in kg.
k=constant
Momentum= p = mass*velocity
= p = mv
= p = kgms
2nd law
F is propotional to p2 - p1/t
is propotional to mv-mu/t
is propotional to m(v-u/t)
is propotional to m*a
F= Kma
since K= i
F= ma
or F= ma
= kgms^2
= Newton (N)
According to this Law each And every action has an equal and opposite reaction.
Important points regarding third law of motion:-
- The action and reaction are forces that act in opposite direction.
- Boyh the forces occures simultaneously.
- Action and reaction are forces which are always equal to each other.
When two bodied collide with each other the total momentum before collision is equal to the total momentum after collision.
- We will now derive this law by newtons third law of motion.
mA= mass of ball A
mB= mass of ball B
UA= initial velocity of ball
UB= initial velocity of ball B
VA= final velocity of ball A
VB= final velocity of ball B
t= time of collision
FAB= force of A on B
FBA= force of B on A
FAB = rate of change of momentum
= ma(VA-UA)
FBA = mB(VB-UB)
According to third law of motion
FAB = FBA
mA(VA-Ua) = mBNB + mBUB
mAVA + mBVB = mAUA + mBUB
1. A bullet escaping from te barrel of a gun moves by inerti, since the action of the powder gases on it ceases after it leave the barrel.
2. A car keeps moving aftr it's engine is switched of.
3. The movement of a gas molecule is an example of movement by inertia. Each move by inertia rectilinearly and uniformly from one collision to another.
4. If the car engine is switched off without breaking, the car does not stop at once.
5. When a horse sudddenly gallops forward, the man sitting on his back may be thrown back unless he presses his thighs hard against the horse.
6. When a car in motion is suddenly stopped, the passengers inside are thrown forward because thir bodies continue in the state of motion in a strightline.
7. If a cyclist, when in sped, applies break suddenly, he is thrown forward because of the tendency of his body to continue in the uniform motion.
8. People usually tumble down when they alite from a train in motion.
9. When a corridor train stops suddenly, sliding doors of some apartments may open or shut due to the inertia of rest or motion.
10. When a tree is shaken the branches move in one direction but the fruits tend to remain in their previous position due to inetia of rest. This causes a break in the contact with the branches and the fruits fall down.
11. When a carpet is beaen with a stick, the carpet comes into motion but the dust particles present in it tend to remainat rest due to inertia of rest. As a result, the dust particles areremoved from it by beating it.
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