1. 8th Grade Investigation 7 Force and Motion
Gravity
8th Grade
Investigation 7
Force and Motion

2. Gravity Gravity: a force pulling masses toward each other.
On Earth, the gravitational force is the force of attraction between Earth (one of the masses) and another object.

3. Gravity
The strength of the gravitational force depends on the size of the masses.
Larger objects pull with more force than do smaller masses.

4. Free Fall Gravity is the force that makes things fall toward Earth.
Because the force applied all of the time, any object that is not retarded by another force will accelerate toward Earth = Free Fall.

5. Acceleration Due to Gravity
All objects fall with the same acceleration when they are in free fall (9.8 m/s2).
Objects like cotton balls & feathers don’t fall as fast as rocks and shoes because they are slowed by air resistance.

6. Air Resistance
Air resistance is like friction, it acts to resist motion.
The force of air resistance acts in the direction opposite to the force of gravity.
The net force pulling the cotton ball toward Earth is less than the force of gravity, so it takes longer to fall than an object in free fall.

7. Free-Fall
The force of gravity makes heavy and light objects free-fall at the same acceleration.
Galileo discovered that objects of different masses fall together, hitting the ground at the same time.
Example: Foil ball vs. paper ball.

8. Force of Gravity
The force of gravity accelerates objects in free fall and objects rolling down hill.
Gravity is a universal force of attraction between masses.

9. Acceleration Due to Gravity
Example: Speedometer - measures speed.
If a boulder dropped from a cliff, it would fall 10 m/s faster than it was in the previous second due to gravity.

10. Acceleration Due to Gravity
The change of velocity in the boulder example is the acceleration due to gravity.
The velocity of an object during its fall can be calculated by the velocity equation: v = a x t