WORK AND ENERGY-Practical
PRELAB
PURPOSE
To demonstrate the validity of the work-energy theorem, and to use energy principles to measure the acceleration of gravity, g.
EQUIPMENT linear
air track, electronic timer, glider, two photogates, pulley and weights,
and shim.
RELEVANT EQUATIONS
DISCUSSION
The work-energy theorem states that the total work W done on an object moving from point A to point B is equal to the difference in the kinetic energies of the object at A and B. The work done on the object is defined as:
where Fx is the magnitude of the component of the force parallel to the direction of motion of the object, and dis the distance the object is moved. The kinetic energy of an object is defined as:
where m is the mass of the
object and v is its speed. In terms of these equations, the work-energy
theorem can be written:
In this experiment, you will
study this relationship on the air-track.
Figure 9-1: Glider on an Inclined Air Track
Figure 9-1 shows an object of mass m sitting on an inclined plane. If the plane is frictionless, the magnitude of the total force parallel to the plane is:
so the work done on m in moving it from A to B, a distance d along the incline, is:
or:
This equation says that
the difference in the square of the speeds of an object at two fixed points
on a frictionless inclined plane is the same regardless of the object's
initial speed.