Gravity Force Lab (AP Physics)

In this experiment, you will use a simulation to measure the gravitation force between two masses. You’ll determine how the strength of the force of gravity depends on the two masses and the distance between them. You’ll also determine a value for the Universal Gravitation constant, G. 
Question:
What is the acceleration of a falling object as determine using:
  • a motion detector
  • video analysis
  • a picket fence falling through a photogate
How do the three methods of determining gravity compare in terms of their accuracy and precision?

Purpose:
To determine the acceleration of a falling object using three different methods and to compare the accuracy and precision of the results of each method.

Learning Objectives aligned with the (Science Practices)
The students will be able to:
  • 1.C.3.1 design a plan for collecting data to measure gravitational mass and to measure inertial mass and to distinguish between the two experiments. (4.2)
  • 2.B.1.1 apply F = mg to calculate the gravitational force on an object with mass m in a gravitational eld of strength g in the context of the effects of a net force on objects and systems. (2.2, 7.2)
  • 2.B.2.1:apply g=GM/r^2 to calculate the gravitational field due to an object with mass M, where the field is a vector directed towards the center of the object of mass M (2.2)
  • 2.B.2.2 approximate a numbers all value of the gravitational field (g) near the surface of an object from its radius and mass relative to those of the Earth or other reference objects. (2.2)
  • 3.C.1.1 use Newton’s law of gravitation to calculate the gravitational force the two objects exert on each other and use that force in contexts other than orbital motion. (2.2)
  • 3.C.1.2 use Newton’s law of gravitation to calculate the gravitational force between two objects and use that force in contexts involving orbital motion. (2.2)
  • 3.G.1.1 articulate situations when the gravitational force is the dominant force and when the electromagnetic, weak, and strong forces can be ignored. (7.1)​


Gravitational Force Lab
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File Type: pdf
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    Newton's Law of Universal Gravitation (10 points)

    PART 1. QUALITATIVE OBSERVATIONS 

    PART 2. QUANTITATIVE MEASUREMENTS 

    Changing Mass 1
    1. Click “Reset All” to get everything back to the original values.
    2. In this part, you will be changing m1, but keeping m2 and the distance between them constant. On your page, record the mass of m2. Use the on-screen ruler to measure the distance between the centers of m1 and m2, and record it on your page.
    3. Make a data table to record the mass of m1 (in kg) and force (in newtons).
    4. For at least 12 different data points, change the mass of m1, and then record the mass and gravitational force in your data table. 
    Changing Mass 2
    1. Click “Reset All” to get everything back to the original values.
    2. In this part, you will be changing m2, but keeping m1 and the distance between them constant. On your page, record the mass of m1. Use the on-screen ruler to measure the distance between the centers of m1 and m2, and record it on your page.
    3. Make a data table to record the mass of m2 (in kg) and force (in newtons).
    4. For at least 12 different data points, change the mass of m1, and then record the mass and gravitational force in your data table. 
    Changing Distance
    1. Click “Reset All” to get everything back to the original values.
    2. In this part, you will be keeping the masses of m1 and m2 constant but changing the distance between them. On your page, record the masses of m1 and m2.
    3. Make a data table to record the distance between the centers of the masses (in meters) and force (in newtons). Leave room for a third column, which you’ll fill in later.
    4.  Move m1 to the left side of the screen. Place the on-screen ruler so that the zero mark lines up with the
      center of m1.
    5. For at least 12 different data points, move m2 to a different location, and then record the distance between
      the masses’ centers, along with gravitational force, in your data table.

    PART 3. ANALYSIS 

    You will have a total of four graphs to draw for this lab, adding these to your Google Sheet.
    • ​Graph 1 uses your data from “Changing Mass 1”. Put mass 1 (in kg) on the horizontal axis and gravitational force (in N) on the vertical axis.
    • Graph 2 uses your data from “Changing Mass 2”. Put mass 2 (in kg) on the horizontal axis and gravitational force (in N) on the vertical axis.
    • Graph 3 uses your data from “Changing Distance”. Put distance (in m) on the horizontal axis and gravitational force (in N) on the vertical axis.
    • ​Graph 3 is not a straight line, so we need to draw Graph 4 to straighten it out so we can analyze it. For all your data points from “Changing Distance”, calculate 1 divided by the distance squared, and write that number in the blank third column in your data table. Graph 4 will have (1/distance^2) on the horizontal axis and gravitational force on the vertical axis
    For each of the straight-line graphs (1, 2, and 4), you should draw a best-fit line and calculate the slope and y- intercept.
    Now let’s figure G, the Universal Gravitation constant.