Newton's Laws of Motion

Newton's Laws of Motion

1. 1st Law

   • 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.

2. 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!

3. 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.