Gravity Investigation Name: Learning Target #14: I am able to use evidence to support the claim that gravitational interactions are attractive and depend on the masses of objects. From acorns to apples, gravity cause nearly any object to fall to Earth s surface. Gravity also causes the Moon to orbit Earth and Earth and the other planets to orbit the Sun. Your task is to explore the factors that affect the gravitational force between two objects using the PhET Gravity Force Simulation found at https://phet.colorado.edu/sims/html/gravity-force-lab/latest/gravity-force-lab_en.html. Before you begin... Before you begin the simulation, consider this question (from Keeley s Assessment Probes): Three friends are talking about gravity. One friend held up a rock and asked his friends whether the gravitational force depended on where the rock was located. Each friend had a different idea about a place where the gravitational force on the rock would be the greatest. This is what they said: Lorenzo: I think if you put the rock on the top of a very tall mountain, the gravitational force on the rock will be greatest. Eliza: I think the gravitational force on the rock will be the greatest when the rock is resting on the ground at sea-level. Flo: I think you have to go really high up. If you drop the rock out of a high flying plane, it will have the greatest gravitational force. Which friend do you agree with most and why? Do you disagree with any of them? Why? Using the Simulation: To begin, make sure the Show Values box is checked. The arrows coming from each object represent gravitational force. The length of the arrow is proportional to the force on each object. Are the arrows pointing towards each other or away from each other?
*NOTE: Gravity is an attractive force.* Part 1: How does mass affect the strength of gravitational force? 1. Drag the two masses so that they are 10 meters apart from each other. (Put the center of the blue mass (m1) directly over the zero on the ruler and the center of the red mass (m2) directly over the ten.) 2. Complete the table below by adjusting the masses of the objects using the arrows or sliders. (There are three blank rows in the table. Please do three trials where YOU choose the values for m1 and m2.) Mass 1 (kg) Mass 2 (kg) Force of m1 on m2 (N) Force of m2 on m1 (N) 50 200 200 200 500 200 800 200 1000 200 1000 1000 3. How does increasing the mass of the objects affect the gravitational force?
Part 2: How does the distance between two objects affect the strength of gravitational force? 4. Set both masses to 100 kg. Put the center of the blue mass (m1) over the zero and the center of the red mass (m2) over the ten. 5. Complete the table below by moving the red mass towards the blue mass. Position of Mass 1 Position of Mass 2 Force of m1 on m2 (N) Force of m2 on m1 (N) 0 10 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 6. How does decreasing the distance between two objects affect the gravitational force? 7. The gravitational force between two objects can be calculated using this formula where G is the gravitational constant (which is 6.7 x 10-11 Nm 2 /kg 2 ) and d is the distance between the two objects. Explain why your results in the tables above make sense based on this equation. (Hint: think about which measurements are in the numerator of the equation and which are in the denominator.)
Part 3: What is the difference between mass and weight? Mass is the amount of matter in an object. It does not change based on where an object is. Weight is the force with which gravity is pulling on a mass. We know from Newton s Second Law that Force = Mass x Acceleration. Since Weight is the Force acting on the object, W can be substituted for F in the equation. F = ma W = ma Near the surface of the Earth, the acceleration due to gravity on all objects is 9.8 m/s 2. We call this value g and write the equation as W = mg Based on what you have learned in Parts 1 and 2 above, you know that the acceleration due to gravity on a mass depends upon the other object too. If the other object is not the Earth, then this value will not be 9.8 m/s 2. The moon, for instance, is about ⅙ the mass of the Earth. Therefore, the acceleration of an object due to gravity on the moon is only about 1.62 m/s 2. That is why the weight of an object is not the same on the Earth as it is on the moon even though the mass of the object did not change. The table to the right shows the acceleration due to gravity for some of the objects in our Solar System. Calculations: Show your work and don t forget the units! 1. A physical science textbook has a mass of 2.2 kg. a. Find the weight of the textbook on Earth.
b. Find the weight of the textbook on Mars. 2. What is the mass of a 70 kg astronaut on the moon? 3. What is the weight of a 70 kg astronaut on the moon? 4. If that 70 kg astronaut has a weight of 775.6 N, what planet is he on? Part 4: Support the Claim Use evidence (from the simulation you completed in Parts 1 and 2) to support the claim that gravitational interactions are attractive and depend on the masses of objects.