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# U of A ASTR 2001L - Gravity Force Lab

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AP Physics – Gravity Force LabToday, you will use the Gravity Force Lab PhET Simulation to investigate what the gravitational force between two objects depends on and experimentally determine the Universal Gravitational constant, G. PreLab and Beginning Observations1) Write the formula for the force of gravity (Law of Universal Gravitation). Label each variable and constant and include its units. Fg = G * m1 * m2 / r^2Fg = force of gravity, NG = 6.673 * 10^-11 m^3 kg^-1 s^-2m1 = mass of object 1, kgm2 = mass of object 2, kgr = distance between two objects, m2) Open the Gravity Force PhET Simulation http://phet.colorado.edu/en/simulation/gravity-force-lab What can you change about the simulation?You can change the masses of the objects and the distance between them.Part 1 – Qualitative Observations 3) Look at the formula above. What three things can you change in the formula that you can also change in the simulation?You can change mass 1, mass 2, and distance between the masses. 4) Change each variable and record what happens to the gravitational force as you change it. Be specific with your language (i.e. use terms like increase, decrease, remains constant).As you increase the mass of either of the objects, the force applied to each other increases, and asyou decrease the mass of either of the objects, the force applied to each other decreases. As you increase the distance between the objects, the force applied to each other decreases, and as you decrease the distance between the objects, the force applied to each other increases.Part 2 – Quantitative Measurements In this section of the lab, you will develop your own method for determining the gravitational constant G in the formula for gravity using the simulation and Excel. Possible ideas ● Change mass 1 and keep mass 2 and the distance constant and record gravitational force. ● Change distance and keep mass 1 and 2 constant and record gravitational force.In both of these examples, think about what you would graph and how it would allow you to determine the constant G. Will your slope represent G only? How much data should you collect given your time constraints? You will submit your procedure, data, graph and value for G. Procedure:1. Keep distance between mass 1 and mass 2 four meters apart throughout whole experiment 2. Make mass 1 50 kg and mass 2 100 kg3. Record gravitational force4. Change mass 1 to 100 kg and and keep mass 2 the same5. Record gravitational force6. Change mass 1 to 200 kg and keep mass 2 the same7. Record gravitational forceData Table:The Effect of Changing Mass on Gravitational ForceGravitational ForceG ( )50 kg 2.0856 * 10^-8 N 6.67392 * 10^-11 m^3/kg*s^2100 kg 4.1712 * 10^-8 N 6.67392 * 10^-11 m^3/kg*s^2150 kg 6.2567 * 10^-8 N 6.67392 * 10^-11 m^3/kg*s^2200 kg 8.3423 * 10^-8 N 6.67392 * 10^-11 m^3/kg*s^2Graph:From the formula :G = 6.67392 * 10^-11

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