General Physics Momentum and Impulse

Recall Newton’s First Law  Inertia was introduced and is the reason that objects follow the first law.  What is Inertia?  The resistance to a change in motion.  From your experience, is it harder to move an object at rest, or stop a moving object?  Does inertia increase because an object is moving?

Momentum  Newton realized that there is a difference between stationary and moving objects.  Newton called this Momentum, which he described as the “quantity of motion”.  The Momentum (p) of an object is the product of its mass and velocity.

Momentum  Momentum is a vector quantity and is in the same direction as the velocity.  The units of momentum are kg m/s.

Momentum in Action  Is it more difficult to change the motion of a large object or a small object?  Is it more difficult to change the motion of a slow moving or fast moving object?  Is it more difficult to stop a slow moving bowling ball or a fast moving softball?

Momentum and Mass  Don’t confuse momentum with mass.  A large mass does not necessarily mean a large momentum.  How much momentum does a loaded freight train have when at rest?  None!!  A flying insect has more momentum.

Changes of Momentum  An object’s momentum can change by gaining or losing mass or speed.  However it is much more likely that it will be a change in speed.  What is required to change an object’s speed?  A Force! According to Newton’s Second Law.

Force and Momentum  An applied force changes momentum.  The larger the force, the bigger the change in momentum.  But it is not that simple.  The time for which the force is applied is also important.  The longer the time, the greater the change.

Impulse  The product of the applied force and the time over which it is applied is called Impulse.  The units of measure are the Newton second (Ns).  The greater the impulse, the greater the change in momentum.

Impulse and Momentum  An Impulse causes a change in momentum.  The impulse imparted to an object is equal to the change in momentum created.

Review  Momentum – the “quantity of motion” The product of an object’s mass and velocity.  Impulse – required to change momentum The product of force and time Equal to the change in momentum.