This lab will demonstrate the principles behind free-fall acceleration. Any object that is thrown or dropped in the presence of gravity experiences constant acceleration. This acceleration is called free-fall acceleration or acceleration due to gravity.
Design an experiment you could construct that might measure free-fall acceleration, and then carry out the virtual lab, beginning on the next screen.
- What materials would you use? What would you measure?
- What results would you expect?
- What if the results were different than expected; what would that indicate?
Write down your answers. You will include a description of your lab and the answers to these questions as part of your lab write-up, which you will submit to your teacher.
In this lab, you will investigate free-fall acceleration on Earth, the Moon, and Mars. You will measure object displacement in free-fall and then calculate its acceleration.
Hypothesize what you think the results of this experiment will be. Will the acceleration you measure be the same in all three environments? How will your measurements compare to accepted values of free-fall acceleration?
Defend your hypothesis with your knowledge of free-fall acceleration. Your answers will be part of the lab write-up, which you will submit to your teacher.
- Analyze motion in terms of the change in distance during a given period of time.
- Summarize the relationships between distance and time for moving objects.
- Interpret graphs relating distance and time for moving objects.
To view the items that need to be included in your lab write-up, along with a grading rubric, please refer to the Guidelines for the Laboratory section of the orientation.
Read all directions before beginning the lab.
- This virtual laboratory is found here: Free Fall Model (you can also find the virtual lab by doing an Internet keyword search for: the physics front free fall model). Download the Free Fall Model to your computer and open it.
- Notice that the lab consists of a motion diagram with an object that can be put into freefall and slide bars for the initial height, initial velocity, and gravitational acceleration. Observe the graphs in the middle of the screen to see the average velocity and average acceleration of a falling body. At the bottom right are a timer, vertical postion measurement and vertical velocity measurement.
- Prepare your spreadsheet to record your data. You will need three tables: one for Earth, one for the Moon, and one for Mars. The first row in each table should be labeled: time (s).
- Make sure the initial velocity is set to zero. Make sure that the gravitational acceleration is set to 9.81 m/s2, the acceleration of gravity on Earth. Slide the initial height to anywhere you choose and observe what happens. You will see the ball drop and the graphs of the position, velocity, and acceleration . When the ball reaches a height of 0 m, the timer will stop. Read the time elapsed on the timer in the lower right corner. To see the ball drop again, click re-start. Do this several times to observe the relationship between displacement and time for the dropping ball.
Displacement of a Falling Object
- Estimate the distance an object would fall in 0.6 seconds. Slide the initial height ruler to this value. Observe the drop. Adjust your estimation and set the initial height again. Repeat this until you determine the distance fallen in 0.6 seconds. Record the distance. Repeat this procedure for each column in the data table for Earth.
- Look up the acceleration of gravity on the moon. Slide the gravitational accleration bar to this value. Repeat the procedure until you have collected time measurements for each of the times in the Moon data table.
- Look up the acceleration of gravity on Mars. Slide the gravitational accleration bar to this value. Repeat the procedure until you have collected time measurements for each of the times in the Mars data table.
|Lab Assignment: Free-Fall Acceleration Laboratory: Analysis
- Organizing Data: For each of the environments, calculate the average velocity. Divide the distance between two time points by the change in time. You might want to create new rows in your spreadsheet with these values. Notice that you will only have five values of average velocity in each location.
- Organizing Data: Using the results from item 1, calculate the average acceleration. Find the change in speed between the first and second time points and the second and third time points, and divide this by the change in time. You may want to add another row to your data tables for these calculations. Notice that you will only have four values of average acceleration.
- Constructing Graphs: Use your data to plot the following graphs for each environment. On each graph, label the axes and indicate the trial number.
- Position versus time
- Velocity versus time
- Acceleration versus time
- Organizing Data: Use the values for the average acceleration for all four trials to find the average value.
- Evaluating Results: Use the accepted value for the free-fall acceleration on Earth given in the text and the average of your results from item 4.
- Determine the absolute error of your results using the equation:
absolute error = |experimental – accepted|
- Determine the relative error of your results using the following equation:
relative error = (experimental – accepted) / accepted
Lab Assignment: Free-Fall Acceleration Laboratory: Conclusions
- Making Predictions: Based on your results, how do the average accelerations on Earth, the Moon, and Mars relate to each other? How did this result compare to your hypothesis?
- Analyzing Graphs: Calculate the slope of each velocity-time graph you made.
- Evaluating Results: Find the average value of the slope of the velocity-time graphs. What is the relationship between this value and the values you found for the average acceleration in each location?
- Analyzing Error: You used a virtual simulation that was programmed with the gravity value on Earth. Why would you still expect to find absolute error and relative error in your measurements of acceleration? How might you do the experiment so that your value of acceleration on Earth would be closer to the accepted value?How did this outcome compare to your hypothesis?
Reminder: Be sure to submit your assignment at this time. Refer to the Guidelines for the Laboratory section for directions on how to submit your assignment to your instructor.
The simulator has changed.We will treat all values as absolute values which means they will be positive. Please use positive values for your graphs and analysis. The negative sign is a convention that indicates the direction as being down toward the Earth but we are free to ignore this for this exercise. Please do not worry about finding the distance for .6 seconds. Enter in 9.8 for the acceleration for Earth. On this simulation you can only go to two significant figures.Set the height to 20 and the initial velocity to zero.By clicking on the “step” button several times you can reach the times that are needed for the data.Once you reach the correct time, you subtract the two Y values and that is how far the object has dropped in that time interval.Please do the same thing for Mars and the Moon except that they have different accelerations (Mars 3.7 and the Moon 1.6)To find the overall average acceleration for each environment, please add up the acceleration values you have for each interval and divide by the number of intervals.Also, you do not need to include trial numbers for your graphs. To check your displacement values, please go to (http://www.ambrsoft.com/CalcPhysics/acceleration/acceleration.htm). Set initial velocity to zero and the acceleration to the desired value. Enter the time value and it will give you displacement (distance). Also, this calculator can be used as an alternative if the simulator won’t run on your computer.
Finding How Far the Object Fell on the Simulator
- FindingYvalueFreeFall.png (86.03 KB)
(picture attached below)
Sample Calculations for Average Velocity and Acceleration on a Time Interval