Section 1 Review State Newton’s first law of motion in your own words List two examples of Newton’s second law of motion. Explain the relation of inertia and seat belts. Determine whether each example is Newton’s first or second law A. a skydiver accelerating toward the ground B. a skydiver falling with constant velocity C. a skydiver on the ground at rest

Section 1 Review State Newton’s first law of motion in your own words List two examples of Newton’s second law of motion. Explain the relation of inertia and seat belts. Determine whether each example is Newton’s first or second law A. a skydiver accelerating toward the ground: 2nd B. a skydiver falling with constant velocity C. a skydiver on the ground at rest

Section 1 Review State Newton’s first law of motion in your own words List two examples of Newton’s second law of motion. Explain the relation of inertia and seat belts. Determine whether each example is Newton’s first or second law A. a skydiver accelerating toward the ground: 2nd B. a skydiver falling with constant velocity: 1st C. a skydiver on the ground at rest: 1st

Section 1 Review State Newton’s first law of motion in your own words List two examples of Newton’s second law of motion. Explain the relation of inertia and seat belts. Determine whether each example is Newton’s first or second law A. a skydiver accelerating toward the ground B. a skydiver falling with constant velocity C. a skydiver on the ground at rest

Chapter 12 Section 2: Gravity

Key Ideas How are weight and mass related? Why do objects fall to the ground when dropped? What is the relationship between free-fall acceleration and mass? Why does a projectile follow a curved path?

Weight and Mass Weight: the force on an object due to gravity Weight is measured in newtons Weight and mass are different Mass: a measurement of the amount of matter in an object Weight: the gravitational force an object experiences because of its mass

Weight influences shape Gravitational force affects the shapes of living things. On land, large animals need strong skeletons to support their mass against the force of gravity. Tall trees need rigid trunks to support their mass. Look at the difference between the legs of a very heavy land animal and those of a much smaller bird. The more massive elephant has a much larger skeleton to support it larger weight. In contrast, the bird has a much smaller mass and can support its weight on long, thin legs.

Law of Universal Gravitation All objects in the universe attract each other through the force of gravity Newton’s law of universal gravitation gives the size of the gravitational force between two objects 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

Free Fall When gravity is the only force acting upon an object, the object is said to be in free-fall Free fall acceleration is directed at the center of the earth In the absence of air resistance, all objects falling near Earth’s surface accelerate at the same rate regardless of their mass. Free-fall acceleration is constant because of the law of universal gravitation

Air resistance can balance weight Both air resistance and gravity act on objects moving through Earth’s atmosphere. A falling object stops accelerating when the force of air resistance becomes equal to the gravitational force on the object (the weight of the object). The reason is that the air resistance acts in the opposite direction to the weight.  When air resistance and weight are equal, the object stops accelerating and reaches its maximum velocity, which is called terminal velocity.

When a skydiver reaches terminal velocity, the force of gravity is balanced by air resistance Astronauts in orbit are in free fall

Projectile Motion The orbit of the space shuttle around Earth is an example of projectile motion Projectile motion: the curved path followed by an object that is thrown, launched, or otherwise projected near the surface of Earth Examples: leaping frogs, thrown balls, and arrows shot from a bow Projectile motion has two components- horizontal and vertical. When the two motions are combined, they form a curved path

Projectile motion has a horizontal component After you have thrown a ball, no horizontal forces are acting on the ball. So, if the horizontal component of velocity of the ball is constant after the ball leaves your hand. Projectile motion also has a vertical component When you throw a ball, gravity pulls it downward which gives the ball vertical motion

Orbiting is a projectile motion An object is orbiting when it is traveling in a circular or nearly circular path around another object.