1. Chapter 17 Objectives Describe gravity and its effect on matter.
Section 4 Gravity: A Force of Attraction
Chapter 17
Objectives
Describe gravity and its effect on matter.
Explain the law of universal gravitation.
Explain how an object’s center of mass is used to determine gravitational force.
Describe the difference between mass and weight.

2. The Effects of Gravity on Matter
Section 4 Gravity: A Force of Attraction
Chapter 17
The Effects of Gravity on Matter
Gravity is a force attraction between objects that is due to their masses.
All matter has mass. Gravity is a result of mass. Therefore, all matter is affected by gravity.
The Size of Earth’s Gravitational Force Compared with all objects around you, Earth has a huge mass. Therefore, Earth’s gravitational force is very large. It pulls everything towards the center of the Earth.

3. Newton and the Study of Gravity
Section 4 Gravity: A Force of Attraction
Chapter 17
Newton and the Study of Gravity
The Core of an Idea The legend is that Newton discovered gravity after watching an apple fall off a tree.
The Birth of a Law Newton summarized his ideas about gravity in a law now known as the law of universal gravitation. This law describes the relationships between gravitational force, mass, and distance.

4. The Law of Universal Gravitation
Section 4 Gravity: A Force of Attraction
Chapter 17
The Law of Universal Gravitation
Part 1: Gravitational Force Increases as Mass Increases The Earth has more mass than the moon does. Therefore, the Earth’s gravitational force is greater than the moon’s.
Part 2: Gravitational Force Decreases as Distance Increases Although the sun’s gravitational force does not have much of an effect on your body here, it does have a large effect on Earth and the other planets.

5. Section 4 Gravity: A Force of Attraction
Chapter 17

6. Relative sizes of earth and moon
Earth’s Mass: 5,973,600,000,000,000,000,000,000 kg
Moon’s Mass: ,470,000,000,000,000,000,000 kg
The moon is 1.2% the mass of earth.
Distance : 450,000 kilometers

7. Relative sizes of sun and earth
Sun’s Mass: 1,989,000,000,000,000,000,000,000,000,000 kg
Earth’s Mass: 5,973,600,000,000,000,000,000,000 kg
The earth is % the mass of the sun.
Distance : 150,000,000 kilometers

8. Gravitational Force and Center of Mass
Section 4 Gravity: A Force of Attraction
Chapter 17
Gravitational Force and Center of Mass
When finding distance between objects to determine gravitational force, scientists always measure from the center of mass of each object.
The center of mass is the point at which all the mass of an object can be considered to be concentrated.

9. Gravitational Force and Center of Mass, continued
Section 4 Gravity: A Force of Attraction
Chapter 17
Gravitational Force and Center of Mass, continued
Finding the Center of Mass The center of mass for regularly shaped objects (spheres and cubes) is in the center of such objects.
For irregularly shaped objects, a simple way to determine the center of mass is to spin the object. The point around which an object spins is the center of mass.

10. Weight as a Measure of Gravitational Force
Section 4 Gravity: A Force of Attraction
Chapter 17
Weight as a Measure of Gravitational Force
Weight is a measure of the gravitational force on an object.
The Difference Between Mass and Weight Weight is related to mass, but they are not the same. Weight changes when gravitational force changes.
Mass is the amount of matter in an object. An object’s mass does not change.

11. Section 4 Gravity: A Force of Attraction
Chapter 17

12. Weight as a Measure of Gravitational Force, continued
Section 4 Gravity: A Force of Attraction
Chapter 17
Weight as a Measure of Gravitational Force, continued
Units of Weight and Mass The SI unit of force is a newton (N). Gravity is a force, and weight is a measure of gravity. So, weight is also measured in newtons. 1 Newton of force = lb.
1 pound = N and 1 kilogram = 9.8 N
The SI unit of mass is the kilogram (kg). Mass is often measured in grams (g) and milligrams (mg) as well. 1 kilogram = 2.2 pounds

13. Weight as a Measure of Gravitational Force, continued
Section 4 Gravity: A Force of Attraction
Chapter 17
Weight as a Measure of Gravitational Force, continued
The Influences of Weight on Shape Gravitational force influences the shapes of living things. Large land animals must have strong skeletons to support their mass against the force of gravity.

14. Chapter 17 Concept Map speed time velocity motion
Matter in Motion
Concept Map
Use the terms below to complete the concept map on the next slide.
speed
time
velocity
motion
acceleration

15. Chapter 17
Concept Map

16. Chapter 17
Concept Map

17. Chapter 17
Section 1 Measuring Motion