5 - PS2 - Gravity - FINAL (WND 1/9/2014)

DCI: PS2.B Types of Interactions – The gravitational force of Earth acting on an object near Earth’s surface pulls that object toward the planet’s center.

PE: 5-PS2-1 Support an argument that the gravitational force exerted by Earth on objects is directed down.

[Clarification Statement: “Down” is a local description of the direction that points toward the center of the spherical Earth.] [Assessment Boundary: Assessment does not include mathematical representation of gravitational force.]

The ideas we see in this standard are: 

- Earth has a gravitational force 

- gravity is a force acting on all objects near Earth's surface

- gravity pulls objects toward the planets center

There is not much content here.  Basically, we can address the idea that gravity is a force acting on all of the objects on Earth and the idea that the direction of the force is downward (towards the center).  In order to address the PE, we can provide students with several explanations about why objects are being pulled down and have them choose the correct one. 

The students clearly do not need to know specifics about the force of gravity, just that it is, in general, pulling objects down towards the center of the earth. 

Possible Question Starters:

"The source of the gravitational force acting on an object near the Earth's surface is - 

correct answer - the center of the Earth

incorrect answer - Earth's atmosphere, the sun, etc. 

"Which of the following examples provides the best evidence that there is a force pulling objects on earth downward?"

correct answer - plant roots growing down

incorrect answer - leaves blowing in the wind

etc.