MOMENTUM
Momentum of a particle (p) is equal to the mass of the particle (m) times velocity of the particle (v). So, p = mv
NEWTON LAWS OF MOTION
(i) First Law (Law of Inertia): Everybody continues in its state of rest or of uniform motion in a straight line unless it is compelled by some external force to change that state.
(ii) Second Law: The rate of change of momentum of a body is directly proportional to the impressed force and takes place in the direction of the force.
So, F = dp/dt
This results force acting a body F is equal to the mass of the body m times acceleration of the body a.
So, F = ma
(iii) Third Law: To Every action there is an equal and opposite reaction.
FAB = - FBA
So, J = Ft
= mv – mu
(a) The lift possesses zero acceleration (fig-1): W = m
(b) The lift moving upward with an acceleration a (fig-2):
W = mg + ma
W= mg + mg
W= 2 mg
(c) The lift moving downward with an acceleration a (fig-3):
W = mg – ma
W = mg – mg
W = 0
NOTE
When the velocity of a body is comparable to the velocity of light, inertial mass changes with velocity in accordance with following formula,
mi = mi0/√(1-v2/c2)
Here mi0 is the rest mass of body, v is the velocity of body and c is the velocity of light.
(b) Driven body moving horizontally:
Acceleration of the system, a = (M /M+m) g
Tension in the string, T= (Mm/M+m) g
The force on the pulley, F= [√2 (Mm) /M+m] g
Here g is the free fall acceleration.
1. What are Newton's laws of motion? |
2. How does friction affect motion? |
3. What factors affect the amount of friction between two surfaces? |
4. How does Newton's first law of motion relate to the concept of inertia? |
5. How does Newton's third law of motion explain the motion of objects in contact? |
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