In order to understand Newton’s second law of motion, we should first know the meaning of the term momentum of a moving body (or moving object).
We know that a cricket ball is much heavier than a tennis ball. Suppose we throw a cricket ball and a tennis ball, both with the same speed or velocity. It will be found that more force is required to stop the cricket ball (Which has more mass) and less force is required to stop the tennis ball (which has less mass). We conclude that the force required to stop a moving body is directly proportional to its mass.
If we throw two cricket balls of the same mass at different speeds or velocities, it will be found that more force is required to stop that cricket ball which is moving with higher velocity and less force is required to stop that cricket ball which is moving with higher velocity and less force is required to stop the cricket ball moving with lower velocity. So conclude that the force required to stop a moving body is also directly proportional to its velocity. Thus the quantity of motion in a body depends on the mass and velocity of the body. This given us another term knows as “momentum” the momentum of a body is defined as the product of its mass and velocity.
Thus, Momentum = Mass x velocity.
Or P = m x v
Where P = momentum
M = mass of the body
and v = velocity (or speed) of the body
It is clear that if a body is at rest, its velocity is zero and hence its momentum is also zero. Thus the total momentum of the gun and bullet before firing is zero because their velocity is zero.Momentum is a vector quantity and takes place in the direction of velocity. We have just seen that momentum is equal to the product of mass and velocity. Now mass is measured in kilograms (kg) and velocity is measured in meters per second (m/s) so the SI unit of momentum is kilogram meters per second which is written as kg m/sEvery moving body possesses momentum. Since momentum depends on the mass and velocity of a body so a body will have a large momentum.
(a) If its mass is large
(b) If its velocity (speed) is large
© If both its mass and velocity (speed) are large.
- A karate player can break a pile of tiles or a slap of ice with a single blow of his hand. This is because a karate player strikes the pile of tiles or the slab of ice with his hand very, very fast.
2.Though a cricket ball is not very heavy but when it is thrown with a high speed (or high velocity) it acquires a very large momentum and sometimes hurts the batsman.
3. A car or bus may not be running at a high speed ( or high velocity) but because of its high mass, it has a very high momentum which may hunt the person coming in its way.From above examples we conclude that the combined effect of mass and velocity of a body is called momentum.