Instructions and Questions to go along with the Gravity and Orbits PhET
Be sure to observe what happens when you do the following:
1) Check the box beside "Gravity Force"
2) Check the box beside "Velocity"
3) Check the box beside "Path"
4) Click the play button and turn gravity from "on" to "off"
For the Sun and Earth system: Draw the path of the Earth with Gravity ON and Gravity OFF
Draw the Sun’s gravitational pull (gravity force) on the Earth & the Earth’s gravitational pull on the Sun
If both the Earth and Sun pull on each other with equal force, why does the Earth move, but the Sun does not move?
You can drag the objects around the screen and move the sliders at the bottom right to change the masses of the objects.
While experimenting DO NOT PRESS PLAY when testing your actions in Question 4. This will add another variable (motion) and confuse your results.
What actions change the force of gravity and How?
(This is indicated by a change in the length of the blue gravity force arrows. DO NOT PRESS PLAY)
Increase the mass of the Sun
Place the sun and earth farther appart
Decrease the mass of the Sun
Place the sun and earth closer together
Increase the mass of the Earth
Increase the velocity of the Earth
Decrease the mass of the Earth
Increased Gravitational Pull
Decreased Gravitational Pull
No change in Gravitational Pull
Based on your results in question 4, what two factors affect the gravitational force between objects?
If the Sun and Earth have gravitational force pulling on the moon, why does the moon orbit the Earth and not the sun?
Choose the picture you think shows the gravity forces on the Earth and Sun. (A longer arrow represents a bigger force, and a shorter arrow represents a smaller force.)
How would these gravity forces change if the Sun got much bigger?
How would these gravity forces change if Earth was much closer to the Sun?
How would these gravity forces change if Earth got much smaller?
How would these gravity forces change if Earth and the Sun were moved farther apart?
Choose the picture of how Earth would move if you "turned off" the force of gravity.
