Physics

Acceleration of Gravity Lab

Name______Date______Period______

Introduction:

In this lab you will investigate an object’s acceleration under the influence of the Earth’s gravity. You will measure distances, calculate average velocity, and then plot your average velocities on a graph of velocity vs. time. Using the graph, the acceleration of gravity (g) can be found.

Objective: To determine the acceleration of gravity from a graph.

Materials:

Acceleration timer, strip of paper, small mass, meter stick or ruler

Procedure:

  1. Set up the timer as shown by your instructor.
  2. Attach a small mass to the paper strip so that as the mass falls, it will pull the paper through the timer. Turn on the timer and release the mass. After the mass hits the floor, turn off the timer.
  3. Mark the end of the paper strip which was attached to the mass. This is the beginning of your strip. Remove the strip from the timer, and remove the mass fro the strip. As the mass dropped, the paper strip moved past the vibrating timer, and the motion of the mass was recorded.
  4. Look at the dots on the paper strip and note that the end attached to the mass has dots very close together. Then the separation becomes greater and greater. At the other end, the dots may start to be closer together because the mass hit the floor. Where increasing separation is obvious, label a dot #1. Then number each dot from there on until you have 15 numbered dots. Make sure that the last dot is not in the area where the dots seem to get closer together or are smeared.
  5. With a meter stick or ruler, measure the distance (change in position) from one dot to the next in meters. For example, dot #1’s change in position would be zero since there is no dot before it to measure it from. Dot #2’s change in position would be measured as the distance, in meters, from dot #1 to dot #2. Measure as precisely as possible.
  6. Use your change in position column and the time interval column to calculate the average velocity of your mass between each dot. To find the average velocity, divide the change in position column by the time interval column. Remember that the change in position number would be put into the calculator first.
  7. Draw a graph of average velocity vs. time (time on x-axis) with the correct units. Use the values from your data table (time on x-axis and average velocity on the y-axis). After you plot the points, draw a straight line through these points. Your line should be a line of best fit. It does not have to go through all the points. Some points may be a little above the line and some may be a little below the line.
  8. Find the slope of the graph by marking two points on the line you just drew. Then use rise/run to calculate your slope. This number should be the acceleration of gravity here on Earth. Please show this work on your graph paper with your graph. Circle your acceleration of gravity.

Questions:

  1. How accurate was your acceleration of gravity on Earth? To find out, use the following formula:

% difference = (your acceleration – 9.8 m/s2)

------X 100

9.8 m/s2

Please show your work on your graph paper and circle your answer.

  1. Do you think you got close enough to the accepted value of the acceleration of gravity on Earth? Why or why not?
  1. When you look at the paper strip, you can tell that the mass is going faster and faster (accelerating). How do you know this?
  1. When you look at the graph, you can tell that the mass is accelerating. How do you know this?
  1. The formula for acceleration is change in velocity divided by time. How do you know that the slope of your line shows acceleration?
  1. What are the units for acceleration of gravity? Does your slope have the correct units? How do you know?
  1. Are there any possible sources of error in your lab? If so, what are they?

Acceleration of Gravity Lab Data Table

Dot # / Change in Position (m) / Time Interval (s) / Average Velocity (m/s)
1 / zero / 0.017
2 / 0.017
3 / 0.017
4 / 0.017
5 / 0.017
6 / 0.017
7 / 0.017
8 / 0.017
9 / 0.017
10 / 0.017
11 / 0.017
12 / 0.017
13 / 0.017
14 / 0.017
15 / 0.017

Hints for lab:

  1. Do not use dots at the very beginning or very end that are smeared together.
  2. An example of how to get the change in position follows: change in position for dot #2 = distance from dot #2 to dot #1.
  3. Please remember to use meters as your unit of position and change of position. You may have to convert from cm or mm to m. To go from cm to m, move your decimal two places to the left. To go from mm to m, move your decimal three places to the left.
  4. The time interval between each dot is 1/60 of a second which equals 0.017 seconds in decimal form.
  5. When you draw your graph in Analysis step 3, please remember to draw a line of best fit – do not connect the dots.
  6. Don’t forget to answer the questions at the end of the lab procedures.