NAME:____________________________ ID#:________________ SECTION:_________




                The inertial mass of an object is a measure of the difficulty in changing the velocity of an object, i.e. accelerating it. It is a measure of the resistance of an object to a change in its state of motion. In the equation F = m X a, the proportionality constant 'm' is a measure of the inertial mass. If we apply the same force to two different objects and their acceleration s are measured to be the same then their inertial masses are equal.


                Gravitational mass is a measure of the attractive force between two objects; for example, the attraction between you and the earth. To measure inertial mass of an object, we apply a force to it and measure its acceleration. Gravity is not a factor in this instance. To measure gravitational mass, we use a balance that compares the gravitational forces acting on two objects. If the gravitational forces are equal, then the masses are equal.




                To study inertial and gravitational mass



                Linear air track, gliders, meter sticks, timers, weak springs, weights, wooden blocks and balances




                In this experiment you will measure the inertial and gravitational masses of air track glider as well as an assortment of other masses which you will place on the glider. Your goal is to determine the relationship between the two types of mass.


1.        Use two weak springs attached on both sides of the glider and to the opposite ends of the air track to supply an accelerating force to the glider (Fig. 1). Your instructor will demonstrate the proper positioning of the springs. Displace the glider about 30 cm and release it. Measure the time required for five (5) oscillations of the glider. Divide the five oscillations by five to get your average time for one oscillation; this is called the period of oscillation. Continue the experiment by adding masses, which will be indicated by your instructor, to the glider and repeating the five oscillations and subsequent determination on the period for each mass. Record all data in Table 1. From your data plot the period of oscillation vs. inertial mass. Attempt to determine the inertial mass of an object of unknown mass and compare your value its gravitational mass when the object is weighed on the balance.




























Figure 1



Table 1






























2.  In this part of the experiment, you will attempt to measure mass using an inclined air track. Use two wooden blocks to raise the end of the air track away from the motor. Place the glider at the top of the incline and measure a distance down the incline from a point on the glider (Fig. 2). You will use this distance as your reference in Table 2. Turn on the air track and allow the glider to come down the track pass the distance you marked off and record the time required in Table 2. Repeat the procedure adding the same masses used in Procedure 1 and record the times required for each mass to travel the designated distance.




















Figure 2






Table 2



DISTANCE (d)  (cm)



Vave (d/t)


Vfinal                                       Vf = 2 X Vave


a  = Vf/t






































Use your data in Table 2 to plot a graph of the gravitational mass vs. acceleration. Attempt to use your graph to determine the gravitational mass of your unknown used in Procedure 1. Explain what happened.





1.        In Procedure 1, why do you think you were asked to do five oscillations instead of just one in determining your period?








2.        In Table 1, how do your inertial mass and gravitational masses compare? Would you expect your answer to be the same if your experiment was performed somewhere other than Earth?







3.        In Procedure 2, what force causes the acceleration of the glider?