Student Exploration: Gravitational Force
Vocabulary: force, gravity, vector
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
On the night of a Full Moon, Mary decides to do an experiment with gravity. At midnight, she climbs into her backyard tree house, leans out the window, and holds an acorn as high as she can. She lets go and is disappointed to see the acorn plummet back down to Earth.
Why did the acorn fall to Earth instead of rising up to the Moon?
Give two reasons why we feel Earth’s gravity more strongly than the Moon’s gravity.
From acorns to apples, gravity causes 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. The Gravitational Force Gizmo™ allows you to explore the factors that influence the strength of gravitational force.
To begin, turn on the Show force vector checkboxes for objects A and B. The arrows coming from each object are vectors that represent gravitational force. The length of each vector is proportional to the force on each object.
Move object A around. As object A is moved, what do you notice about the direction of the two force vectors?
How do the lengths of the two vectors compare?
Drag object A closer to object B. How does this change the gravitational force between the two objects?
Gravity and mass
Get the Gizmo ready:
Turn on Show vector notation for each object.
Check that each object’s mass (mA and mB) is set to 10.0 • 105 kg.
Question: How does mass affect the strength of gravitational force?
Form hypothesis: How do you think the masses of objects A and B will affect the strength of the gravitational force between them?
Predict: How do you think the gravitational force between two objects will change if the mass of each object is doubled?.
Measure: Turn on Show grid. Place object A on the x axis at -20 and object B on the xaxis at 20. The force on object A is now 0.0417i + 0j N. That means that the force is 0.0417 newtons in the x direction (east) and 0.0 newtons in the y direction (north).