1. Gravity
What’s Got You Down?

2. Difference between mass and weight
You know this already. Turn to a partner nearby and explain the difference between the two.
Mass – the measure of the amount of matter in an object
Weight – the force of gravity on a person or object at the surface of a planet

3. Gravity – motion of falling objects
Gravity is a force that pulls objects toward each other
We know that the Earth pulls you toward its center.
Do you pull the Earth toward you?
Yes – but you are so little compared to the Earth that this pull is not noticeable.

4. Gravity – motion of falling objects
When the only force acting on an object is gravity, the object is said to be in free fall.
An object in free fall is accelerating. Do you know why?
In free fall, the force of gravity is an unbalanced force, which causes an object to accelerate. The object is continually pulled toward the Earth as it falls, therefore it will accelerate.

5. Gravity – motion of falling objects
We are going to do a couple of activities with falling objects. Make sure you make very careful observations while doing the activities!

6. Gravity – motion of falling objects
Use your book as a reference to look up and write down the following answers:
How much do objects accelerate as they fall?
Do all objects accelerate at this rate?
What causes some objects to accelerate more slowly toward the Earth than others?
What is a projectile?
How does the horizontal movement of a projectile affect its acceleration toward the Earth?

7. Universal Gravitation
Hold your pen or pencil up over your head
Now let go of your pencil.
What happened?
Why?
Sir Isaac Newton pondered this very same question.

8. Universal Gravitation
Here is what Sir Isaac Newton concluded:
A force acts to pull objects straight down toward the center of Earth.
He then went on to generalize this and said:
Gravity is a force that pulls objects toward each other.

9. Universal Gravitation
The law of universal gravitation states that the force of gravity acts between all objects in the universe.
This means that any two objects in the universe attract each other, without exception.
All of the objects around you are attracted to you. However, you do not notice the attraction because these forces are small compared to the force of Earth’s attraction.

10. Universal Gravitation
Two factors affect the gravitational attraction between objects:
Mass
Distance

11. Universal Gravitation
The more mass an object has, the greater its gravitational force.
The farther apart two objects are, the lesser the gravitational force between them.