MS - PS2.B (B) - Gravitational Forces - FINAL (CLF 2/5/2014)

Module: Gravitational Forces

DCI: PS2.B (B) Gravitational forces are always attractive.  There is a gravitational force between any two masses, but it is very small except when one or both of the objects have a large mass –eg, Earth and the sun.

PE: MS-PS2-4 Construct and present arguments using evidence to support the claim that gravitational interactions are attractive and depend on the masses of interacting objects.

[Clarification Statement: Examples of evidence for arguments could include data generated from simulations or digital tools; and charts displaying mass, strength of interaction, distance from the Sun, and orbital periods of objects within the solar system.] [Assessment Boundary: Assessment does not include Newton’s Law of Gravitation or Kepler’s Laws.]

The ideas we see in this standard are: 

- gravitational forces are always attractive

- there is a gravitational force between any two masses

- gravitational forces are very small except when one or both of the objects have a large mass (like the Earth and the Sun). 

In order to 'construct and present arguments', we will, again, have to provide about either an object's mass, or the magnitude of a gravitational attraction and ask them to relate it back to the object's mass.  Although the clarification statement mentions distance from the Sun, that really only applies to the modules on planetary movement, and probably should not be included as a factor here. Also, students should not have to calculate any forces. 

We can get one or two general content questions out of this, but for the most part, they should include some set of data. 

Possible Question Starters: 

"When comparing the gravitational force between two objects, which of the following characteristics of the objects should be considered?"

correct answer - mass

incorrect answer - volume, state of matter, etc. 

Another way to ask a general question is from an "application" perspective.
"The gravitational force between two objects will be very small, unless which of the following is true?"
- Both objects must have a very large mass*
- Only one object must be very massive
- The objects must be very close together
- One of the objects must be much larger 

We might also ask about how gravity works.
- always pulls objects towards each other
- always pushes objects away
?

We can ask a "general" data question
"What data would support the claim that the gravitational force between objects depends on mass?"
*gravity is stronger on more massive planets
- the gravity of the earth can be "escaped"?