PhET Activity for MS-PS2-1: Gravity Force Lab

DIRECTIONS:
1. You are starting in the initial state of the simulation. Observe the two masses, m1 (blue, 100 kg) and m2 (red, 400 kg).
2. Notice the ruler between them, showing their positions in meters.
3. Look at the top of the screen to see the force values displayed in decimal notation.
4. Locate the control panels for 'Mass 1' and 'Mass 2' at the bottom of the simulation.
5. Find the 'Force Values' panel on the bottom-right, which allows you to change how the force is displayed.
Spend 2-3 minutes freely exploring the simulation. Drag the masses left and right. Use the sliders in the control panels to change their mass. Observe how the force vectors (arrows) and the numerical values at the top of the screen change. Do not worry about recording any data yet.

QUESTION: Are you acquainted with the tools in this simulation?

DIRECTIONS:
1. Click the orange reset button on the bottom-right to return to the initial state.
2. Observe the initial force value with m1 at 100 kg.
3. Using the 'Mass 1' control panel at the bottom-left, drag the slider all the way to the right to set its value to 1000 kg.

QUESTION: As the mass of m1 increases while m2 and the distance stay the same, the gravitational force between the two objects (a)   .

DIRECTIONS:
1. Do not reset. Mass 1 should still be at its maximum value (1000 kg).
2. Now, use the 'Mass 2' control panel in the bottom-center.
3. Drag the slider for Mass 2 all the way to the right to set its value to 1000 kg.

QUESTION: You already increased the force by raising m1's mass. What happened to the force when you also increased m2's mass?

DIRECTIONS:
1. Click the orange reset button.

2. 2. Change the 'Force Values' to 'Scientific Notation'.
   3. Set Mass 1 (m1) to 200 kg.
   4. Set Mass 2 (m2) to 400 kg (its default value).
   5. Note the force value at the top of the screen.
   6. Now, double the mass of m1 to 400 kg.
   
   QUESTION: When the mass of one object is doubled, the gravitational force between the two objects also ___. This shows a ___ proportional relationship.

DIRECTIONS:
1. Click the orange reset button.
2. Observe the initial distance between the centers of the masses (m1 is at 2m, m2 is at 6m, so the distance is 4m). Note the force value.
3. Click and drag the red mass (m2) to the right until its center is at the 10m mark on the ruler. The distance is now 8m.

QUESTION: As the distance between the two masses increases, the gravitational force between them (a)   .

DIRECTIONS:
1. Click the orange reset button.
2. Drag the blue mass (m1) to the 4m mark and the red mass (m2) to the 6m mark. The distance between them is 2m. Record the force value.
3. Now, double the distance by dragging the red mass (m2) to the 8m mark. The distance is now 4m.
4. Observe the new force value.

QUESTION: When you double the distance between the objects, what happens to the gravitational force?

DIRECTIONS:
1. Click the orange reset button.
2. Using the 'Mass 1' control panel, set m1 to its minimum value of 10 kg.
3. Using the 'Mass 2' control panel, set m2 to its maximum value of 1000 kg.

QUESTION: Even though m2 is 100 times more massive than m1, how does the force m1 exerts on m2 compare to the force m2 exerts on m1?

DIRECTIONS:
1. Do not reset. Keep Mass 1 at 10 kg and Mass 2 at 1000 kg.
2. Click and drag either mass to change the distance between them. Move them very close and then very far apart.

QUESTION: Explain in your own words why the force of gravity on each object is always the same magnitude, even when their masses and the distance between them change. Relate this to Newton's Third Law.

DIRECTIONS:
1. Click the orange reset button.
2. Set both Mass 1 and Mass 2 to 1000 kg.
3. In the 'Force Values' panel on the bottom-right, click the 'Scientific Notation' button.

QUESTION: Scientific notation is a useful way to write very ___ or very ___ numbers concisely.

(a)  

DIRECTIONS:
1. Do not reset. Keep both masses at 1000 kg and the force display in 'Scientific Notation'.
2. In the 'Force Values' panel, make sure the 'Constant Size' checkbox is unchecked.
3. Drag m2 far to the right, then drag it very close to m1.

QUESTION: What do the arrows above the masses represent?