Work and Energy Physics 1

The Purpose of a Force  The application of a force on an object is done with the goal of changing the motion of the object.

Accomplishment of Forces  A force (F) will achieve a change in motion when it: acts in the direction of motion change. OR has a component in the direction of motion change.

Accomplishment of Forces

Definition of Work  The product of the displacement and the force component acting in the direction of displacement is called work.

Definition of Work  When a force F is applied to an object of mass m, the object accelerates from an initial velocity v i to a final velocity v f.

Definition of Work  If the object is displaced  d, the work W done by the force F is:

Definition of Work  From

Definition of Work  The quantity of mechanical work produced by an accelerating force was defined as.

Kinetic Energy  Eventually this quantity of mechanical work became known as kinetic energy (KE ).  Today kinetic energy is defined as the energy an object possesses due to its motion.

Work-Energy Theorem  The amount of mechanical work done to accelerate an object is equal to the change in the object’s kinetic energy. This is called the work-energy theorem.

Potential Energy  When work is done a resistive force, potential energy (PE) is created equal in magnitude to the work done.  Potential energy is sometimes called stored kinetic energy.

Gravitational PE  When an object is lifted a distance h in the earth’s gravitational field, work is done against the force of gravity creating gravitational E P.

Elastic PE  The resisting force of a compressed or stretched spring is directly proportional to the displacement. (Hooke’s Law) spring constant

Elastic PE  When a spring is compressed or stretched a distance x, work is done against the elastic force of the spring creating elastic PE.

Mechanical Energy  The total kinetic energy and potential energy possessed by an object is called its mechanical energy (ME).

Conservation Law  In the absence of friction, the total mechanical energy remains the same. This is statement is called the Law of Conservation of Mechanical Energy.

Rate of Work  The rate at which work is performed is called power (P ).

Rate of Energy  Power can also be defined as the rate at which energy is created.