Physics Lab Report

ABSTRACT

The lab of one dimensional motion is a series of experiments that deal with different types of motion in a single direction. In the first experiment, one dimensional motion of a small cart on an air track is measured in a one photogate system. The acceleration was calculated by the infrared light emitting electrode of the photogate sensing the slacks on the picket fence.

The calculation for gravity yielded 9.63 m/s^2, which is consistent with the accepted value of 9.8m/s^2. In the second experiment, acceleration of a cart traveling down a slight incline was measured with a two photogate method. Gravity was calculated and yielded a value of 8.7429, a bit lower than the accepted value of 9.8 m/s^2. The third experiment was the measurement of acceleration due to a horizontal force, a pulley system with a weight attached. The acceleration was measured with a single photogate. Gravity was calculated to be 9.209m/s^2 which is slightly lower that the accepted value of 9.8m/s^2.

In the final experiment, a sonic range finder was used to calculate the properties of walking motion including distance, time, velocity, and acceleration. The starting acceleration was calculated to be .3778m/s^2 and the negative acceleration was calculated to be -.4844m/s^2.

INTODUCTION TO THEORY

The one dimensional motion measurements are going to be done on an air track. The air track is a triangularly shaped track studded with small holes which emit air. A corresponding triangularly shaped cart is placed on top of the track and will move on a cushion of air to take away friction. Hence, the study of acceleration can be done without the inaccuracies that friction brings.

Figure 1.1 The Air Track

A photogate is a u shape measuring device that is placed above the track. An infrared light emitting diode (source) and a photodiode (sensor) are placed on each side of the U-shaped frame. The photogate is considered unblocked as long as the sensor is picking up the infrared light. When something passes through the photogate, the sensor is blocked from the source and a signal is sent to the computer. In this labs case, a picket fence is placed on top of the cart and is positioned to pass through the photogate while the cart is in motion. A picket fence is a rectangular shaped plastic composed of an alternating order of transparent and black slits. The photogate is blocked while the black slits are in between the sensor and source but it is unblocked when the transparent component is in between the source and sensor. The photogate is able to measure the relative times that the photogate is blacked and unblocked.

The slats on the picket fence are positioned at a set distance delta X apart. Each slat will block the photogate momentarily as the picket fence passes through. The computer can then measure the relative times that the photogate is blocked and unblocked.

Figure 1.2 The picket Fence

In the First experiment, acceleration of gravity will be determined using the one photogate method. The acceleration of a cart will be measured traveling down an inclined plane. The computer will measure the timing of the slats traveling through the photogate and produce an acceleration. The acceleration down an inclined plane is related to gravity by equation 1.1. Sin is the angle of the incline plane.

A = g sin (?)

1.1

In the second experiment, a two photogate system is used to determine the value of g by allowing the near frictionless cart to move down an inclined ramp. The only difference is two photogates will be used to find the change in velocity. Instead of a picket fence there will be a metal flag with a measured width. The flag will pass through each photogate which will measure the lengths of time that each photogate is blocked, the same way that it did in the single photogate method but with a different series of calculations since, a picket fence is not being used. The time that the first photogate is blocked will be called delta T1. The second length of time will be the time in between when the first photogate is blocked until when the second photogate is unblocked (deltaT12). The third time measured will be the time that the second photogate is blocked (deltaT2). The average velocity that it takes for the flag to pass through each photogate will be calculated by the change in the known distance of the flag divided by the time it takes to pass through the photogate in question. The acceleration of the cart can then be calculated by equation 1.2.