1. Chapter 4 Lesson 21 TCAP Coach
Gravity
Chapter 4
Lesson 21
TCAP Coach

2. Objectives
SPI Recognize that the Earth attracts objects without touching them.
SPI Identify the force that causes objects to fall to the Earth.
SPI Use data to determine how shape affects the rate at which a material falls to Earth.

3. Gravity You know what happens when you jump up into the air.
You push off the ground, rise, and then move back toward the ground.
When you throw a ball up into the air, you know what will come back down.
These things happen because of a force called gravity.
In this lesson, you will investigate gravity and learn about the factors that affect it.

4. The Force of Gravity
Gravity is an attractive force that pulls objects toward each other.
Gravity attracts objects even if the objects do not touch.
You probably think of gravity as a force pulling objects toward the ground.
In our everyday life, gravity really pulls objects toward Earth’s center.
But this force acts everywhere in the universe- not just on Earth.

5. The Force of Gravity
Any object with mass exerts a force of gravity that pulls on objects around it.
The more mass an object has, the greater its pull of gravity.
Gravity keeps you from floating off into space.
Gravity helps keep the moon in orbit around Earth.
Gravity also helps keep Earth in orbit around the sun.

6. The Force of Gravity
Just as you are attracted to Earth, Earth is also attracted to you.
You only notice the force that Earth exerts on you because your attractive force is so much smaller.
The force of gravity depends on two factors. These two factors are mass and distance.

7. How Mass Affects Gravity
Recall that mass is the amount of matter in an object.
An object with more mass has a greater force of gravity than an object with less mass.
Think about an apple and Earth.
Both objects pull on each other because they both have mass. But because the apple’s mass is so small, its force of gravity is very small.
It does not pull very strongly on Earth.

8. How Mass Affects Gravity
Earth has much more mass than an apple.
That means Earth has a larger force of gravity than the apple.
This causes you to see the apple moving toward Earth rather than Earth moving toward each other.
Earth only moves the tiniest amount because Earth’s pull is so much greater than that of the apple.

9. How Distance Affects Gravity
The second factor that determines the force of gravity between two objects is their distance from each other.
As objects move closer together, their pull on each other grows.
As objects move farther apart, their pull on each other weakens.

10. How Distance Affects Gravity
Think of a spacecraft traveling toward another planet.
As the spacecraft moves away from Earth, Earth’s pull on it decreases.
As the spacecraft moves closer to another planet, the other planet’s pull increases.

11. How Distance Affects Gravity

12. Friction and Air Resistance
When objects fall to Earth’s surface, gravity is not the only force that acts on them.
Friction also affects their motion.
Friction is a force that acts between the surfaces that touch each other.
Friction tends to slow an object’s motion.

13. Friction and Air Resistance
When an object falls through the air, its surface bumps into air particles.
Friction between a moving object and air particles is called air resistance.
Air resistance acts against the pull of gravity to slow a moving object.

14. Friction and Air Resistance
Air resistance depends on an object’s shape and surface area.
A folded parachute falls to the ground much faster than an open parachute.
An open parachute’s cupped shape causes it to hold and touch more air particles as it falls.
Its large surface area also gives it more air resistance.
That slows a sky diver’s fall to the ground.

15. Friction and Air Resistance

16. 1. The force of gravity will be greatest between Earth and
A. an object with a mass of 4 kg.
B. an object with a mass of 30 kg.
C. an object with a mass of 200 kg.
D. an object with a mass of 1000 kg.

17. 1. The force of gravity will be greatest between Earth and
D. an object with a mass of 1000 kg.

18. 2. How does the distance between objects affect the force of gravity between them?
A. The greater the distance, the greater the force of gravity.
B. The smaller the distance, the greater the force of gravity.
C. The smaller the distance, the smaller the force of gravity.
D. Distance has no effect on the force of gravity.

19. 2. How does the distance between objects affect the force of gravity between them?
B. The smaller the distance, the greater the force of gravity.

20. 3. Which BEST describes the gravitational attraction between an apple and Earth?
A. Earth attracts the apple.
B. The apple attracts Earth.
C. The apple and Earth attract each other.
D. The apple has no gravity.

21. 3. Which BEST describes the gravitational attraction between an apple and Earth?
C. The apple and Earth attract each other.

22. 4. Which two objects have the MOST gravitational attraction toward each other?
A. two basketballs one foot apart
B. two golf balls one foot apart
C. one basketball and one golf ball one foot apart
D. two basketballs two feet apart

23. 4. Which two objects have the MOST gravitational attraction toward each other?
A. two basketballs one foot apart