11-Sept-2016： Free Fall Lab--determination of g (and learning a bit about Excel) and some statistics for analyzing data

Apparatus: A free fall equament with a spark generator, a paper tape, and ruler.

Purpose: To examine the validity of the statement: In the absence of all other external forces except gravity, a falling body will accelerate at 9.8 m/s^2

Model: d=1/2gt^2  (d is distance, g is gravity, and t is time)

Process: Professor pulls a piece of paper tape between the vertical wire and the vertical post of the device. He clips it with a weight to keep the paper "tight". Then, he turns the dial hooked up to the electromagnet up a bit and hangs the wooden cylinder with the metal rin around it on the electromagnet. He turns on the power on sparket thing and holds down the spark button on the sparker box. He turns the electromagnet off so that the thing falls, and then he turns off the sparker thing. Finally, he tears off the paper strip.
    We take sixteen consecutive points. We let the first point as the “zero”, and then we measure the distance between each point and the zero point. 
    This sparker work at 60 Hz. Therefore, the time between each point is 1/60 seconds.
    We puts the data (time, distance, Δx, Mid-interval time, and Mid-interval speed) into computer on Excal, and uses the Excal to get the graph.

In cell A1 enter TIME.
In cell A2 enter 0.
In cell A3 enter =A2+1/60

In cell B1 enter DISTANCE
In cell B2 enter 0
In cell B3 enter the date from the second point to the last point.

In cell C1 enter Δx
In cell C2 enter =(B3-B2)
Fill down

In cell D1 enter Mid-interval time
In cell D2 enter =A2+1/120
Fill down

In cell E1 enter Mid-interval speed
In cell E2 enter =C2/(1/60)
Fill down

Use the Chart-Chart Layout

    Let the Mid-interval speed be the y-axis and the Mid-interval time be the x-axis. Fit the points into the linear equation. Then we can get the relationship between speed and time. According to v=gt (v is Mid-interval speed, g is gravity, and t is Mid-interval time).
    By the data that Excal figure out, the gravity basing on our data is 9.50 m/s^2


Part 2: Error and Uncertainty--Physics 4A

    We collect the "gravity" that every group get.

    Model:  
    (N is the number of the "gravity", μ is the average "gravity", and Xi is the each "gravity")

In cell A1 enter Value of g
In cell A2 though A11, enter tehr class' values for g from the spark tape free fall experiment.
In cell A12 enter =average(a2:a11)

In cell B1 enter dev form mean
In cell B2 enter =a2-$a$12
Fill down

In cell C1 enter dev^2
In cell C2 enter =sum(A2:A11)
Fill down

    The Standard Deviation of the Mean of the class' data is 28.27.