can someone please explain newtons first and second law simply

Question

mani_jha · Answer

Newton's first law defines inertia. It is the resistance to change of state of motion of rest. It simply means that you can't move any stationary object or stop/speed up/slow down anything in the world without applying any external force on it. This is because every thing has mass, and it resists change in its state.
It also means that a box moving on a frictionless road(think of it as ice) will move forever at the same speed, because like every other form of matter, it has mass, and will resist change in its state,  unless an external force is applied. But since friction is absent, there is no external force at all, and the box's state will never change.

mani_jha · Answer

Newton's second law defines force and momentum. You've seen above that an external force causes a change in state, more specifically, a change in speed. The amount of force needed to change the state depends not only on the change in speed, but also the mass(Just think, a small bullet moving at high speed would hurt you more than a car moving slowly). Hence, force must be related to a quantity called momentum, which  is mass times velocity.
The law states that whenever an external force is applied onto something, it causes a change in momentum(more specifically speed; mass generally remains constant). This change in momentum is directly proportional to the force applied(more the force applied, more the momentum changes).
$$F=dp/dt$$
$$p=mv$$
$$F=m(dv/dt)$$
Thus,
$$F=ma$$
Clear?

anonymous · Answer

Newton's First Law of Motion:

I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
This we recognize as essentially Galileo's concept of inertia, and this is often termed simply the "Law of Inertia".

Newton's Second Law of Motion:

II. The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector.