Lab 4

For lab 4 we were asked to find the initial acceleration of an elevator when it starts and stops. To do this we were given a force probe attached a 550 gram weight and stand that would measure the change in force as the elevator accelerated. 

Before we could do this we had to first calculate the amount of force that gravity was putting on the probe itself in order to subtract it from our findings in the elevator. After zeroing the probe we found that gravity placed roughly 5.1 newton’s of force on the probe, with this information in hand we quickly sketched a set of a motion diagram, force diagram, and force addition diagram. We calculated that the elevator would have its forces cancelled out by both the tension in the cable and the force of gravity until the moment of acceleration, at which point the motor in top of the elevator shaft would either increase tension to make the elevator go up or decrease it to make it stop and equalize. We would then be able to calculate the elevators acceleration by dividing the change in force by the velocity, giving us the acceleration.

Armed with this information we proceeded to the elevator and took a single reading from the start of the elevators trip to the bottom to its stop at the bottom floor that provided the following chart from logger pro.

From this information we were able to discover the force at the time of acceleration at the elevators beginning and ending. Logger pro calculated the force at approximately 5.1 at the beginning as the elevator traveled downwards and increased to 5.8 at its stop in order to counteract its velocity downwards and 5.3 for its constant movement. We then subtracted the constant force of gravity, 5.1 from each reading to find the change in force, calculating to -.3 net force for the initial downwards acceleration and a .4 increase for the upwards acceleration to cease moving and a constant .2 difference. 

We then plugged this information into the formula Weight*Acceleration=Force, giving us 550*A=5.1, which after dividing the force by the weight to isolate acceleration gave us 0.009 Meters per second for start, and then did the same for its acceleration to stop, calculating to 0.010, keeping the force relatively the same for the elevator. To calculate the speed of the elevator we divided this number by the weight of the weight attached to the recorder in kilograms, calculating that the average speed of the elevator was .36 Meters per second. A fairly comfortable pace for an elevator that takes roughly 9 seconds to go between floors.

Possible problems.

Gaining the information for an elevator is not always exact as it can be difficult to time the movement of the elevator with when the graph starts and ends, we were lucky, but we may have missed some critical data. Additionally we always needed to take the averages of the information and that can sometimes be skewed by large temporary readings, like the short hikes that the graph shows for the initial movements of the elevator.