Gravity

1. Gravity Chapter 4 Lesson 21 TCAP Coach

2. Objectives • SPI 0507.12.1 Recognize that the Earth attracts objects without touching them. • SPI 0507.12.2 Identify the force that causes objects to fall to the Earth. • SPI 0507.12.3 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