Newton’s First Law of Motion
“An object at rest will stay at rest, and an object in motion will stay in motion unless acted on by a net external force"
This means that motion cannot change or decrease without the effect of an unbalanced force. If nothing happens to you, you will never go anywhere. If you’re going in a certain direction, unless something happens to you, you’ll always go that way forever.
That is, if the resultant force (the vector sum of the forces acting on the body) is zero, then the velocity of the object is constant. When we say that the velocity of an object is constant, we mean that both magnitude and direction are constant.
Examples
The electric fan continues to move for a period after the electricity is turned off.
Fall back forward when the stationary bus starts to move.
Newton’s Second Law of Motion
“If a force affects an object, the object gains acceleration, proportional to its strength and inversely proportional to its mass.”
Newton’s second law studies the movement of an object when external forces affect it. When a constant force affects a huge object, it causes it to accelerate, that is, to change its speed, at a constant rate.
In the simplest case, the force acting on an object at rest causes it to accelerate in the direction of the force. However, if the object is indeed in motion it may appear that the object is speeding up, slowing down, or changing its direction depending on the direction of force, directions taken by the object, and the frame of reference in which it is moving Relative to each other.
This relationship applies the principle of preserving the momentum, which is that when the sum of the resultant forces acting on the object is equal to zero, the momentum of the object remains constant. The resultant force is equal to the rate of change in the momentum.
This law also means that when two equal forces act on two different bodies, the object with greater mass will have less acceleration and slower motion, and the object with less mass has greater acceleration. For example, to illustrate:
If we have two similar engines, one for a large car and the other for a small car, then the small one will have more acceleration because its mass is less and the large one will have less acceleration because its mass is greater.
Newton’s Third Law of Motion
“For every action, there is an equal and opposite reaction.”
All forces in the universe occur in equal but oppositely directed pairs. There are no isolated forces; for every external force that acts on an object there is a force of equal magnitude but opposite direction which acts back on the object which exerted that external force.
In the case of internal forces, a force on one part of a system will be countered by a reaction force on another part of the system so that an isolated system cannot by any means exert a net force on the system as a whole. A system cannot “bootstrap” itself into motion with purely internal forces, to achieve a net force and an acceleration, it must interact with an object external to itself.
Engineers apply Newton’s third law when designing rockets and other devices, for example, the rush of gases from the rocket to the top when it ignites causes it to increase its speed.
When a person walks it affects the earth strongly and the earth also strongly affects it so both the earth and the person affect each other.
When you jump, your feet apply force to the ground, and the earth applies an equal and opposite reaction force that pushes you into the air.
When a person is in water, the water pushes the person forward while the person pushes the water back, both affect each other.