The experiment can be made more complex by putting an extra weight into one cart, so that the masses of the carts are unequal.

All gliders are equipped with a 5 cm tab which interrupts the light beam when passing through the photocell gate. The timing system can be set to measure the time, ta or tb, a tab takes to move through the gate or the time, tab, taken for the glider to move from gate A to gate B (not B to A). The timer can be set at full scale ranges from 99.9 ms through 999 seconds for a range of applications.

One timer is set so that it records the time for a glider to move from A to B. The second timer is set to measure the time the tab requires to move through gate A, and then after resetting, the time required for the tab to move through gate B. The acceleration, to an accuracy of less than about ten percent, can be computed using the equation:

where v1=5cm/ta and v2= 5cm/tb.

Note: IMPORTANT NOTE: This demonstration uses BOTH photocell timing devices. You cannot do this demonstration and any other that uses photocell gates without major setup changes during class. We suggest that you do not request this demonstration for the same class as any other photocell timing demonstration.

All gliders are equipped with a 5 cm tab which interrupts the light beam when passing through the photocell gate. The timing system can be set to measure the time, ta or tb, a tab takes to move through the gate or the time, tab, taken for the glider to move from gate A to gate B (not B to A). The timer can be set at full scale ranges from 99.9 ms through 999 seconds for a range of applications.

One timer is set so that it records the time for a glider to move from A to B. The second timer is set to measure the time the tab requires to move through gate A, and then after resetting, the time required for the tab to move through gate B. The acceleration, to an accuracy of less than about ten percent, can be computed using the equation:

a = (v2-v1)/tab = mg/(M+m). where v1=5cm/ta and v2= 5cm/tb.

This can be compared with the component along the air track at the angle a: a = g sin a.

Rest the tube on the lecture table. Lift one end to obtain constant acceleration. Lift one end of the tube and immediately place it back on the table to obtain constant velocity.

Rolling a sphere down a uniform incline led Galileo to some of the earliest conclusions regarding motion with a constant acceleration and to information regarding the acceleration of gravity on the earth.

The ultrasonic range detector is used with a computer to plot graphs of position, velocity, and acceleration. Linear motion can be created by a person walking along a line in front of the ultrasonic ranger. A large piece of styrofoam sheet can be used as a reflector for the ultrasound, to keep the curves as smooth as possible. Graphs of x, v, and a can be easily displayed individually or in any combination.

The graphs of position and velocity are quite nice, but the acceleration can be a bit noisy, because it is obtained by differentiation of the position vs. time data. Try this before class.

Load the arms with equal masses at the same or different distances from the center, and observe what happens when the cart is accelerated by hand along the track. Alternatively, load the arms with masses in the ratio of 10:1 which look the same, and ask students to account for the behavior of the apparatus. By lifting one end of the track, show that when a force (gravity) is allowed to act uniformly on all parts of the apparatus the crossarm will not rotate regardless of how it is loaded.

A simple demonstration sequence is to place more mass on one side (at front in pictures above) and accelerate the cart with your hand to illustrate inertial mass, then let the cart accelerate down the inclined track to illustrate gravitational mass.

Compare the real experiment to this similarly designed simulation by Erik Neumann at MyPhysicsLab. The simulation lets you adjust the mass of the "carts," the stiffness of the springs, and other variables.