1. Gravity
Key Concepts
What factors affect the gravitational force between two objects?
Why do objects accelerate during freefall?

2. Key Terms Gravity Mass Weight Free fall Air resistance
Terminal velocity
projectile

3. What is gravity?
Sir Isaac Newton concluded that a force acts to pull objects straight down toward the center of the Earth
Gravity is a force that pulls
objects toward each other

4. What is Universal Gravitation?
The force of gravity acts between all objects in the universe
Any 2 objects in the universe attract each other

5. What are the Factors Affecting Gravity?
Two factors affect the gravitational attraction between objects: mass and distance
Mass - a measure of the amount of matter in an object (atoms)
SI unit of mass is kilogram - 1 kilogram is the mass of about 400 pennies = 2.2 pounds

6. What are the Factors Affecting Gravity?
Mass – more mass an object has, the greater its gravitational force
The sun’s mass is so great that it exerts a large gravitational force on the planets – One reason why they stay in orbit
Distance – the farther apart two objects are, the less gravitational force between them

7. How are Weight and Mass related?
Mass is the measure of the amount of matter in an object
Weight is a measure of the gravitational force exerted on an object
Weight varies with the strength of the gravitational force, but mass does not
Mass weight gizmo

8. How does gravity affect motion?
Free fall –occurs when gravity is the only force acting on an object
An object in free fall is accelerating because the force of gravity is an unbalanced force

9. Free Fall
Near the surface of the Earth the acceleration due to gravity is 9.8m/s2
For every second an object is falling its speed increases by 9.8 m/s
All objects in free fall accelerate at the same rate

10. How does Air Resistance Affect Gravity?
Objects falling through air experience a type of fluid friction called air resistance
Friction is a force in the opposite direction of motion so air resistance is an upward force
Falling objects with greater surface area experience more air resistance
In a vacuum there is no air, all objects fall at the same rate of acceleration

11. How does Air Resistance Affect Gravity?
Air resistance increases with velocity
Eventually the falling object will fall fast enough that the upward force of air resistance will equal the downward force of gravity
At this point, the forces are balanced and the objects stops accelerating
The object continues to fall at constant speed
This is called terminal velocity – when the force of air resistance = weight of the object

12. Terminal Velocity

13. What is Projectile Motion?
Projectile - An object that is thrown
Will an object that is thrown horizontally land on the ground at the same time as an object that is dropped?

14. What is Projectile Motion?
The force of gravity still acts on the object in the same way. It falls downward at the same rate of acceleration as a ball that has been dropped

15. ProjectileMotion

16. What is Projectile Motion?
If you throw an object at an upward angle, the force of gravity will reduce its vertical velocity until it stops.
Then the force of gravity will pull it back to the ground
When it falls it will accelerate at 9.8m/s2
Goalfinder

18. Sources http://www.aps.org/publications/apsnews/200510/zerogravity.cfm