PHYSICAL SCIENCE

EXPERIMENT 3 (COMPUTERIZED VERSION)

UNIFORM MOTION

NAME: _______________________________ ID #: _________________ SECTION: _______ DATE: _______

INTRODUCTION

An object that is undergoing a change in position is said to be moving.  The motion may be either simple straight-line motion, where the change in distance is the same for each period of time, or may be very complex, as in a tumbling satellite orbiting the earth.  Our study in this experiment deals with simple straight-line motion with uniform change in the distance, and straight-line motion with uniform change in the velocity.  A good example of straight-line motion is the movement of a glider along a linear air track.  A close observation of the glider will reveal that its position changes at a uniform rate;  that is, the distance traveled is the same for equal periods of time.  We can say it another way – the distance traveled is directly proportional to the time.  This can be written as

Distance  (s) is proportional to (    )  time (t)

Or            s = v t

_                                                                                                               _

Where v (pronounced v bar) is a proportionality constant.  Solving for v, we obtain

v  =  s / t

The quantity v is known as the average velocity of the glider.

An object whose velocity is changing is said to be accelerating.  The velocity may be increasing, decreasing, or changing direction.  Any of these causes a change in the velocity.  In this experiment we will be dealing with a change in velocity due to an increase.  In observing the glider traveling down the incline plane, you will discover that the velocity change will be the same for equal periods of time.  This means that the velocity change is directly proportional to the change in time.  This can be written as

Change in velocity (  v)       Change in time (    t)

or                                                                            v  = a  x       t

Where "a" (acceleration is a proportionality constant.  Solving the equation for "a" we obtain

a  =         v  /   t

Since   v  =  vf  -  v0

Where    a = acceleration of the glider;

v0 = original velocity of the glider;

vf  = final velocity of the glider; and

t  = change in time

OBJECTIVES

1.                    To study objects moving at constant velocities.

2.                    To study objects moving at constant accelerations.

APPARATUS

Linear air track, glider, meter stick, timer.

PROCEDURE

1.                    The air track will be assembled and leveled by the laboratory technician.  Please do not attempt any adjustments of the air track.  If you have trouble, ask the instructor for assistance.

Place the glider in motion by applying a very small force of the glider in a direction parallel to the air track.  Do not attempt to move glider if air supply is not turned on.  Determine the time required for the glider to travel the distances listed in Data Table 3.1. Calculate the velocity v as called for in the data table.  Several students should work together, each having a timer, and take simultaneous time readings of each pass of the glider along the track.

Data Table 3.1  YOUR DATA WILL BE IMPORTED FROM XCEL FILE

(Graph number one)  Plot the experimental results with time t on the x-axis and the distance s on the y-axis.  Determine the slope of the curve:

Slope  = Y2 - Y1 / X2 - X1

2.             When Procedure 1 has been completed adjust the air track at an angle with the table top.  This can be done by placing one or more blocks under the end of the air track away from the motor.  In this position the glider will have an acceleration along the air track.

Place the glider on the air track and determine the time required to travel the distances given in Data Table 3.2.  Calculate the value of vf and a, as called for in the table.  Make the calculations with the glider starting from rest.  The quantity vf is the instantaneous velocity at the distance indicated, that is, the velocity at the end of 100cm, or 150 cm, or 200 cm, and so on.  The average velocity can be determined as follows:

_

v   =  vf  -  v0 /  t

Where v = average velocity

vf  =  instantaneous velocity at the distance indicated and

v0 = velocity at rest

Since the glider is started from a condition of rest, v0  =  0, so

v  =  vf  /  2

and                                         vf  =  2  v

Substituting   s / t   for v yields

vf  =  2  s / t

The acceleration is constant; therefore its value can be calculated from a definition of acceleration, which can be written

a  =  vf  -  v0  /  t

In this calculation,  v0 has the value of zero.  Check the result using the equation (a = 2 s / t2).

(Graph number two)  Plot the experimental data with time t on the x-axis and the velocity vf on the y-axis.  Determine the slope of the curve.

TABLE 3.2  (YOUR DATA WILL BE IMPORTED FROM XCEL FILE

QUESTIONS

1.                    Distinguish between velocity and acceleration.

2.                    How is the slope of a curve determined?

3.                    How does the distance traveled vary with time in uniform linear motion?

4.                    How does the distance traveled vary with time in uniform accelerated motion?

5.                    In Procedure 1, what is the relation between the velocity and the slope of the curve?

6.             In Procedure 2, what is the relation between the acceleration and the slope of the curve?