Lab # ? Human Power

Human Power

Purpose:
 To determine the power output of a person.
Equipment:
 Two meter sticks, stopwatch, kilogram bathroom scale.
Introduction:
 Power is defined to be the rate at which work is done or equivalently, the rate at which energy is converted from one form to another. In In this experiment we did some work by climbing from the first floor of the science building to the second floor. By measuring the vertical height climbed and knowing our mass, we were able to calculate our gravitational potential energy:
m=mass
g= acceleration
h= vertical height gained

DeltaPE=mgh

To calculate Power= (delta PE)/ (delta t)

Procedure:
We determined each member's mass by weighing on a scale and used Logger Pro to convert our weight in kilograms to Newtons. We measured the vertical distance between the ground floor and the second floor of the science building by using a 2m meter stick. We recoded 4.26 m for all groups. A record keeper was assigned and the groups took turns to record the time that each team member took to run/walk up the stairs.
Then we calculated the personal power output in watts with the data collected.
The average of the entire class was 541watts.

Conclusion:
Using the hand railing to assist you in your climbing up the stairs is not necessarily a source of error so in this case it is not important. This is because it only increases the amount of energy needed to get up the stairs, it changes the results but does not contribute an incorrect value. The same goes for changing the time it takes for the person to climb up the stairs, skipping steps, walking/running, jumping off; still does not mean the value is incorrect, it just changes the results.
Some of the real sources of error could be measuring the height from the ground floor to the second floor, measuring the weight of each member, significant figure rounding errors, timing, etc., since this can directly change our calculation and give us an incorrect value. Also,
An important source of error that was not mention in the class discussion was the fact that we only took one trial per person and not two as it was directed on the lab, meaning that we didn't have an average to make sure the value for the "human power" was as accurate as possible. For sample calculation and data table see below.

 

Drag Force on a Coffee Filter

Lab Report #7 Drag Force on a Coffee Filter

Purpose:

to study the relationship between air drag forces and the velocity of a falling body.

Procedure: Using a packet of nine coffee filters, Logger Pro software and motion sensor we measured the drag force of the paper filters. To make sure that our results were more accurate and consistent we made sure the shape of the packet of filters stayed the same throughout the experiment.

This is because drag is affected by the surface area of the object as well so, the greater the surface area the greater the drag force will be and vice versa, the smaller the surface area of the object the smaller the drag force will be therefore, to keep a somewhat constant surface area it is important to keep the shape for all the filters the same. If the filters were separated then the data collected from the results of the experiment would not be as accurate or precise.

We let the filters fall from a height of 1.5 m right above the motion detector; we collected the data from each of the nine coffee filters, removing one at a time, five different runs each. My first prediction on how the graph would look like was that it would be a curve concave down, similar to the graph of gravity because I acceleration was still involved. After the experiment I found that the correct graph looks sort of linear and that the Speed is actually constant.

We examined the position vs. time graph obtained with the help of Logger Pro, selecting a small range of data points near the end of motion where the pocket moved with constant speed; we excluded the points where the motion was not uniform. Using the linear curve fit feature in Logger Pro (y=mx + b) we found the slope of the graph to be -0.8068 m/s The slope represents a constant velocity, which is the velocity of the drag.

We also created a second graph using Logger Pro with number of filters vs. average terminal speed. By using the Power law fit of the data we recorded the power "n" given, n=2.070 and we found that our percent error was 3.5% based on our calculations using the %error formula: ((real-exp.)/(real))x100% where  the real/accepted value for “n” is 2.00

 

 

 

Conclusion:

 Based on our observation we have concluded that drag is directly proportional to weight of the packet and consequently drag force depends on the speed of the object. Comparing drag force equation Fdrag= ¼(Av^2), to equation Fd=kabs[v] ^2 1 from the Lab we determined that exp=2= air drag accepted value, k=A=some constant and v=Average velocity. The fit parameter represents the some of the key points we already talked about. For example, Graph number 2 shows the relation between average velocity and the # of coffee filters/ weight; we can say that as the # of coffee filters/weight increase, the average velocity increases too.

Some of the sources of greater error or areas where the experiment could be improved to obtain more accurate results from the experiment would be to drop the coffee filters at the same height, the same way each time. Also, the pack of coffee filters may not have been exactly the same for each run because the filters would impact the floor each time and they might have suffered some deformation so, the air drag would slightly change each time in a way that might not have changed if the surface area of the packet was not disturbed.

Physics 4A Lab #4: Working with Spreadsheet

Purpose:

 The purpose of the lab was to get familiar with the electronic spreadsheet by using them in some simple calculations.

Equipment:

Computer with Excel software

Procedure:

The first part was to create a simple spread sheet that calculates the value of the function f(x)=Asin(Bx+C). We chose values for A=5, B=3 and C=∏/3 representing amplitude, frequency and phase. Then we made two columns, one for "x" another one for “f(x).” on the cell bellow "x" we entered zero, on the cell below "f(x)" we entered an equal sign and followed by the formula above. We created a column for values of “x” running up to 10 radians in increments of 0.1 radians and by using the same feature we created the values for “f(x)”. Our next step was to copy the data from the two columns in the spreadsheet to the graphical analysis program and create a graph matching the corresponding data. We selected a portion of the graph; then we used sine curve fit from the list of possible functions. Comparing the values for A, B and C displayed by the computer to the spreadsheet’s were very similar. A and B values were exactly the same, C value was off by 0.47. See tables bellow.

 

We repeated the same process for another spreadsheet that calculated the position of a freely falling particle as a function of time. This time our constants included the acceleration of gravity, initial velocity, initial position and the time increment, so we used the values g=9.8m/s/s, Vo=50m/s, Xo=1000m and for time intervals ∆t=0.2 s. the equation used in this case was quadratic y= A+Bx+Cx^2 where A= g acceleration, B= initial velocity and C= initial position. Again the values for the variables that we started with in the spreadsheet match the values from the graph. See tables bellow.

Conclusion:

The hardest part of the assignment was to figure out how to enter the equation in the spreadsheet so it could give us the right data. We made several attempts to match the value of the original variables to those obtained from the graphical analysis and they did not match which meant that we made a mistake on setting up the equation. We had to go back several times and fix it until we got it right. For us the biggest source of error did not know how to use Excel software.

Other sources of error or a way in which the calculation could have been more precise could be by making the increments in time smaller for example instead of using 0.1 s; we could have used 0.01 s or 0.001 s. In my opinion the most important step was to correctly set up the equation in the spreadsheet and to identify the right function to curve fit the graph. Through this lab I learned the importance of knowing how to use tools that will allow you to make calculation faster and more efficiently to obtain/measure data for each experiment.

 

 



First Day in Physics 4A