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 this experiment you will do some work by climbing from the first floor of the science building to the second floor. By measuring the vertical height climbed and knowing your mass, the change in your gravitational potential energy can be found:

Δ PE = mgh

Where m is the mass, g the acceleration of gravity, and h is the vertical height gained. Your power output can be determined by

Procedure:

1. We determine our mass by weighing ourselves bathroom scale in kilograms. Record your mass in kg.

2. Measure the vertical distance between the ground floor and the second floor for the science building.

3. We designate a record keeper and a timer for the class. At the command of the timing person, run or walk up the stairs from the ground floor to the second floor

4. We then repeat one more trial.

5. We calculate our personal power output in watts using the data collected from each of your climbing trip up the stairs. We obtain the average power output from the two trials.

6. We then calculated it in horse powers.

 

Questions: 1. Is it okay to use your hands and arms on the handrailing to assist you in your climb up the stairs? Explain why or why not.  It is okay because we are measuring the whole power of the body.  

2. Discuss some of the problems with the accuracy of this experiment : one factor might be the fact that maybe not everyone was walking/running the other and also human error in the stop watch and measurement of the floor.

Conclusion:

I learned how to calculate the power of a person. And also how to convert it into horse power.  Are percent error compared to class is shown above:

This is due to the fact that everyone was not walking/running the same as the other in the groups.

Centripetal Force

Centripetal Force

Purpose: To verify Newton’s second law of motion for the case of uniform circular

motion.

Equipment:

Centripetal force apparatus                               metric scale

vernier caliper                                                   stop watch

slotted weight set                                            weight hanger

 triple beam balance

Introduction:

The centripetal force apparatus is designed to rotate a known mass trough

a circular path of known radius. By timing the motion for a definite

number of revolutions and knowing the total distance that the mass has

traveled, the velocity can be calculated. Thus the centripetal force, F,

necessary to cause the mass to follow its circular path can be

determined from Newton’s second law.

F= (mv^(2))/r

Where m is the mass, v is the velocity, and r is the radius of the circular

path.

Here we have used the fact that for uniform circular motion, the

acceleration, a, is given by: a=(v^2)/r

Procedure:

1. For each trial we position of the horizontal crossarm and the vertical indicator

post must be such that the mass hangs freely over the post when the spring is

detached. After making this adjustment, we connect the spring to the mass and

practice aligning the bottom of the hanging mass with the indicator post while

rotating the assembly.

2. We measured the time for 50 revolutions of the apparatus. Keep the velocity as

constant as possible by keeping the pointer on the bottom of the mass aligned with

the indicator post. We placed a white sheet of paper as a background behind the

apparatus that was helpful in getting the alignment as close as possible. Using the

same mass and radius ,we measure the time for three different trials. Record all data

in a neat excel table as shown below.

3. Using the average time obtained above, calculate the velocity of the mass. From

this calculate the centripetal force exerted on the mass during its motion.

4. We determine the centripetal force by attaching a hanging weight to

the mass until it once again is positioned over the indicator post this time at rest.

Since the spring is being stretched by the same amount as when the apparatus was

rotating, the force stretching the spring should be the same in each case.

5. We then calculated the centripetal force as shown below.

• Conclusions:

o What did you learn? I learned how to calculate centripetal force of an object moving in an circular motion and also learned how to calculate the velocity of an object in centripetal motion.

o Discuss possible sources of error. Possible sources of error might include our constant velocity of while rotating. And also the spring’s movement was radical moving to much or to little.

o Can you think of ways to redesign/improve this lab? Maybe finding a way to keep constant velocity actually constant.

Drag force on a coffe filter

                                           Drag force  on a coffe filter
                   

Purpose: To study the relationship between air drag forces and the velocity of a falling body.

Equipment: Computer with Logger Pro software, lab pro, motion detector, nine coffee filters, meter stick

Introduction:

When an object moves through air, it experiences a drag force that opposes its

motion. In this lab we are going to investigate the velocity dependence of the drag force.

We will use the equation Fdrag = k |v|n, where the power n is to be determined by the experiment.                

This lab will investigate drag forces acting on a falling coffee filter. Because of the large surface

area and low mass of these filters, they reach terminal speed soon after being released.

Procedure:

Why is it important for the shape to stay the same? Explain and

use a diagram. It is important for the filter to stay the same shape because we need the surface area to be the same.

 

1. We logged into the computer with username and password. Start the Logger Pro software, open the Mechanics folder and the graphlab file. Then we Set the data collection rate to 30 Hz.

2. Place the motion detector on the floor facing upward and hold the packet of nine filters at a minimum height of 1.5 m directly above the motion detector. We started the  collecting data, and then release the packet. What should the

position vs time graph look like? Explain. The coffee filters should decreased in position at a constant velocity (when the graph made a straight line) just before they hit the ground.

3. We then used the curve fitting option from the analysis menu to fit a linear curve (y = mx + b) to the selected data. We then Record the slope (m) of the curve from this fit. What should this slope represent? Explain. The slope should represent terminal velocity.

 We then repeat this measurement at least 8 more times, and calculate the average velocity. And record all

data in an excel data table as shown below.

4. We then carefully remove one filter from the packet and repeat the procedure in parts 2 and 3 for the remaining packets of eight filters.  We keep removing filters one at a time and repeating the above steps until we finish with a single coffee filter. As shown in the above data table. We then print a copy of one of your best x vs t graphs that show the

motion and the linear curve fit as shown below.

5. We then used Graphical Analysis, create a two column data table with packet weight in one

column and average terminal speed (|v|) in the other. We Made a plot of packet weight (y-axis) vs. Terminal speed. Choose appropriate labels and scales for the axes of your

graph. We made sure to remove the “connecting lines” from the plot. Perform a power law fit of the data and record the power, n, given by the computer. We obtain a printout of your graph as shown below:

  We then check the % error between the experimentally determined n and the theoretical value . Our B value is equal to n which is 2 since the original equation shows v^2. Our value for B was 2.21. We can calculate our percent error with the equation:

% error = |(accepted-experimental)/accepted| X 100

% error = |(2-2.21)/2| X 100

% error = 10.5%

We then calculated area as shown below : we can find the surface area of the coffee filters since the k value is constant.

k = A

A = 1.39

k = 1.39

k = (1/4)A

1.39 = (1/4)A

A = 5.56

And finally a calculation for the original equation F(drag) = (1/4)Av^n

A=5.56

V=9.89m/s

N=2.22

=220N

Conclusion: Based on the experimental terminal velocity average was 2.22 and the original was 2 based on are percent error that was 10.5%. We had a high percent error meaning we did not take to account several things including air current in the room . Other things that could have been a factor included filters position on top of each meaning the air that goes between each filter if not properly stacked.