Newton's first law of motion states that a body will remain in its state of rest or uniform
motion in a straight line unless acted upon by a resultant force.
Also called the Law of Inertia
Inertia is the resistance of all bodies to change in
their initial state of rest or uniform velocity.
Mass is a measure of Inertia
An object with a larger mass has a more Inertia.
When you kick a bowling ball and a tennis ball with the same
force, the tennis ball will move much more than the bowling ball.
Because the bowling ball has a greater mass and more inertia.
Meaning that once an object moves, it will keep moving in a straight line.
But this doesn't happen in our daily lives
because friction causes objects to stop moving.
Friction is the resultant force.
If you continuously push the object to keep it moving, the
force you apply on the object is also a resultant force.
A body moving with constant velocity
experiences zero net/resultant force.
2nd Law
Newton's second Law of Motion states that the rate of change of momentum is proportional to the
resultant force acting on it and acts in the direction of the resultant force.
Momentum: mass x velocity
Note: both the mass and velocity can change! Not everything has constant mass.
For a body with constant mass, F=m x difference in velocity/ time=mass x acceleration.
F=ma
When F=ma is used in the context of a free falling object, you will get its weight, W=mg.
When resultant force is zero, there is no acceleration.
This compliments Newton's first Law of motion!
3rd Law
Newton's third Law of Motion states that is Body A exerts a force on Body B, Body
B will exert an equal and opposite force on Body A.
The forces exerted by both Body A and B are termed as action-reaction pairs.
Action-reaction pairs are 2 forces (same type of force) acting in opposite directions from each other.
The forces could be acting at a distance away from each other.
Or they could be contact forces.
Force exerted by a book on a table and force exerted
by the table on the book.
Eg. Gravitational force of attraction exerted by Moon on Earth and the gravitational
force of attraction exerted by the Earth on the Moon.
Magnetic forces of repulsion between like poles of a magnet.
The action and reaction forces do not act on the same body, so they do
not balance to produce zero resultant fore on a single body.