Chapter 12 Section 2 Gravity Objectives Explain that gravitational force becomes stronger as the masses increase and rapidly becomes weaker as the distance between the masses increases. Evaluate the concept that free-fall acceleration near Earth’s surface is independent of the mass of the falling object. Demonstrate mathematically how free-fall acceleration relates to weight. Describe orbital motion as a combination of two motions.

Law of Universal Gravitation Section 2 Gravity Law of Universal Gravitation Sir Isaac Newton (1642–1727) generalized his observations on gravity in a law now known as the law of universal gravitation. Universal Gravitation Equation m1 and m2 are the masses of the two objects d is the distance between the two objects G is a constant

Law of Universal Gravitation, continued Section 2 Gravity Law of Universal Gravitation, continued All matter is affected by gravity. Two objects, whether large or small, always have a gravitational force between them. When something is very large, like Earth, the force is easy to detect. Gravitational force increases as mass increases. Gravitational force decreases as distance increases.

Law of Universal Gravitation Section 2 Gravity Law of Universal Gravitation

Law of Universal Gravitation Section 2 Gravity Law of Universal Gravitation

Section 2 Gravity Free Fall and Weight Free fall is the motion of a body when only the force of gravity is acting on the body. Free-fall acceleration near Earth’s surface is constant. If we disregard air resistance, all objects near Earth accelerate at 9.8 m/s2. Freefall acceleration is often abbreviated as the letter g, so g = 9.8 m/s2.

Free Fall and Weight, continued Section 2 Gravity Free Fall and Weight, continued Weight is equal to mass times free-fall acceleration. weight = mass  free-fall acceleration w = mg Weight is different from mass. Mass is a measure of the amount of matter in an object. Weight is the gravitational force an object experiences because of its mass.

Comparing Mass and Weight Section 2 Gravity Comparing Mass and Weight

Free Fall and Weight, continued Section 2 Gravity Free Fall and Weight, continued Weight influences shape. Gravitational force influences the shape of living things. Velocity is constant when air resistance balances weight. The constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity is called the terminal velocity.

Section 2 Gravity Terminal Velocity

Free Fall and Motion Orbiting objects are in free fall. Section 2 Gravity Free Fall and Motion Orbiting objects are in free fall. The moon stays in orbit around Earth because Earth’s gravitational force provides a pull on the moon. Two motions combine to cause orbiting.

Two Motions Cause Orbiting Section 2 Gravity Two Motions Cause Orbiting

Section 2 Gravity Free Fall

Projectile Motion and Gravity Section 2 Gravity Projectile Motion and Gravity Projectile motion is the curved path an object follows when thrown, launched, or otherwise projected near the surface of Earth. Projectile motion applies to objects that are moving in two dimensions under the influence of gravity. Projectile motion has two components—horizontal and vertical. The two components are independent.

Section 2 Gravity Projectile Motion

Projectile Motion and Gravity, continued Section 2 Gravity Projectile Motion and Gravity, continued Projectile motion has some horizontal motion. Horizontal motion is motion that is perpendicular (90º) to Earth’s gravitational field. The horizontal velocity is constant. Projectile motion also has some vertical motion. The vertical motion is the same as downward free-fall motion.

Section 2 Gravity Projectile Motion