Coach Book Lesson 8: Gravity

Gravity

Gravity is a force that pulls all objects with mass toward one another. A gravitational attraction exists between any two objects with mass.

Gravitational force between two objects depends on their masses and on the distance separating them.


Acceleration Due to Gravity
Earth's gravity causes the speed of any falling object to increase steadily. This rate is 9.8 m/s^2.

Air Resistance

The reason for different fall rates between a bowling ball and a feather is air resistance, a form of friction. Friction slows an object's motion. Air resistance acts against the pull of gravity.
If Earth had no atmosphere, would the bowling ball or the feather hit the ground first?

Properties of Matter

The amount of matter in an object. An objects mass is the same at any location in the universe.

Mass

A measure of the pull, or force, of gravity on an object. The metric unit of force is a Newton.

Weight

Multiple Choice

Two objects are moving away from each other. What happens to the gravitational attraction between them?

• 
  it decreases

• 
  it becomes zero

• It increases

• Nothing changes

Multiple Choice

Which of the following statements about gravitational fields is true?

• 
  Gravitational fields affect objects only when two objects are touching.

• Any object that has mass is surrounded by a gravitational field.

• Gravitational fields affecting objects only if the objects are not in contact.

• Only very massive objects, such as Earth, are surrounded by a gravitational field.

Multiple Choice

When a rocket attempts to launch, its engine exerts a force downward. The rocket will not launch until the force of the engine is greater than the weight of the rocket. Why?

• 
  The forces must be equal and balanced for the rocket to move.

• The force of the engine must be greater than the force of gravity to produce a net upward force.

• The rocket must move at a constant velocity to take off.

Multiple Choice

If an object falls far enough, it will reach terminal velocity. At this velocity, the force of air resistance is equal to the force of gravity on the object. The forces on the falling object are balanced. What will happen to the object and why?

• The object will accelerate toward the ground because gravity is pulling on it.

• The object will fall at a constant velocity because the forces on it are balanced.

• 
  The object will hover in midair because the forces on it are balanced.

• 
  The object will decelerate, or slow down, until it reaches a full stop at the ground.