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Chapter 13 Physical Science

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**Preview Section 1 Gravity: A Force of Attraction**

Chapter 13 Forces and Motion Preview Section 1 Gravity: A Force of Attraction Section 2 Gravity and Motion Section 3 Newton's Laws of Motion Concept Map

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Chapter 13 Forces and Motion

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**The Law of Universal Gravitation, continued**

Section 1 Gravity: A Force of Attraction Chapter 13 The Law of Universal Gravitation, continued The force of gravity depends on the distance between two objects. As the distance between two objects gets larger, the force of gravity gets much smaller.

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Chapter 13 Forces and Motion

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Chapter 13 Forces and Motion

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Chapter 13 Forces and Motion

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**Air Resistance and Falling Objects**

Chapter 13 Section 2 Gravity and Motion Air Resistance and Falling Objects Air resistance is the force that opposes the motion of objects through air. Air resistance slows the acceleration of falling objects. The amount of air resistance acting on a falling object depends on the size, shape, and speed of the object.

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**Air Resistance and Falling Objects, continued**

Chapter 13 Section 2 Gravity and Motion Air Resistance and Falling Objects, continued An object falls at its terminal velocity when the upward force of air resistance equals the downward force of gravity. An object is in free fall if gravity is the only force acting on it.

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**Air Resistance and Falling Objects, continued**

Chapter 13 Section 2 Gravity and Motion Air Resistance and Falling Objects, continued Because air resistance is a force, free fall can happen only where there is no air. The term vacuum is used to describe a place in which there is no matter. Vacuum chambers are special containers from which air can be removed to make a vacuum.

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**Projectile Motion and Gravity**

Chapter 13 Section 2 Gravity and Motion Projectile Motion and Gravity Projectile motion is the curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth. Projectile motion is made of two different motions, or movements: horizontal movement and vertical movement. When these two movements are put together, they form a curved path.

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**Projectile Motion and Gravity, continued**

Chapter 13 Section 2 Gravity and Motion Projectile Motion and Gravity, continued Horizontal movement is movement parallel to the ground. Gravity does not affect the horizontal movement of projectile motion.

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**Projectile Motion and Gravity, continued**

Chapter 13 Section 2 Gravity and Motion Projectile Motion and Gravity, continued Vertical movement is movement perpendicular to the ground. Gravity affects the vertical movement of an object in projectile motion by pulling the object down at an acceleration of 9.8 m/s2 (if air resistance is ignored).

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Chapter 13 Forces and Motion

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Chapter 13 Section 2 Gravity and Motion Orbiting and Gravity An object is orbiting when it is moving around another object in space. The two movements that come together to form an orbit are similar to the horizontal and vertical movements in projectile motion.

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Chapter 13 Forces and Motion

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**Orbiting and Gravity, continued**

Chapter 13 Section 2 Gravity and Motion Orbiting and Gravity, continued The path of an orbiting object is not quite a circle. Instead, the path is an ellipse. Centripetal force is the unbalanced force that makes objects move in an elliptical path. Gravity provides the centripetal force that keeps objects in orbit.

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**Orbiting and Gravity, continued**

Chapter 13 Section 2 Gravity and Motion Orbiting and Gravity, continued Gravity helps maintain the shape of the solar system by keeping large objects such as the planets in their orbit around the sun. Gravity also affects the movement of very small objects in the solar system, such as the tiny particles that make up the rings of Saturn.

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**Section 3 Newton's Laws of Motion**

Chapter 13 Newton’s First Law Newton’s first law of motion states that the motion of an object will not change if the forces on it are balanced. Newton’s first law of motion describes the motion of an object that has a net force of 0 N acting on it.

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**Newton’s First Law, continued**

Section 3 Newton's Laws of Motion Chapter 13 Newton’s First Law, continued An object that is not moving is said to be at rest. Objects at rest will not move unless acted upon by an unbalanced force. Objects in motion will continue to move at a constant speed and in a straight line unless acted upon by an unbalanced force.

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**Newton’s First Law, continued**

Section 3 Newton's Laws of Motion Chapter 13 Newton’s First Law, continued Friction is an unbalanced force that changes the motion of objects. Because of friction, observing Newton’s first law is often difficult. Newton’s first law of motion is sometimes called the law of inertia.

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**Newton’s First Law, continued**

Section 3 Newton's Laws of Motion Chapter 13 Newton’s First Law, continued Inertia is the tendency of an object to resist being moved or, if the object is moving, to resist a change in speed or direction until an outside force acts upon the object. Mass is a measure of inertia. An object that has a small mass has less inertia than an object that has a large mass.

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**Newton’s Second Law of Motion**

Section 3 Newton's Laws of Motion Chapter 13 Newton’s Second Law of Motion states that the acceleration of an object depends on the mass of the object and the amount of force applied. describes the motion of an object when an unbalanced force acts on the object.

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**Newton’s Second Law of Motion, continued**

Section 3 Newton's Laws of Motion Chapter 13 Newton’s Second Law of Motion, continued The greater the mass of an object is, the greater the force needed to achieve the same acceleration. The acceleration of an object is always in the same direction as the net force applied. An object’s acceleration increases as the force on the object increases.

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Chapter 13 Forces and Motion

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**Newton’s Third Law of Motion**

Section 3 Newton's Laws of Motion Chapter 13 Newton’s Third Law of Motion Newton’s third law of motion states that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. All forces act in pairs. When a force is exerted, there is always a reaction force.

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**Newton’s Third Law of Motion, continued**

Section 3 Newton's Laws of Motion Chapter 13 Newton’s Third Law of Motion, continued Action and reaction force pairs are present even when there is no movement. A force is always applied by one object on another object. However, action and reaction forces in a pair do not act on the same object.

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Vocabulary Gravity- the force of attraction between objects; unbalanced force Mass- a measure that does not change when an object’s location changes; a measure of the amount of matter. Weight- the measure of gravitational force exerted on an object; expressed in the SI unit of force, the newton (N). Static- nonmoving, or, objects. law of universal gravitation- gravitational force is related to mass and distance.

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**Vocabulary (continued)**

terminal velocity-This is the constant velocity of a falling object when the force of gravity is balanced by the force of air resistance. Free fall-motion of a body when only the force of gravity is acting on the body (ONLY IN A VACUUM) Inertia- All objects tend to resist any change in motion. Orbital motion- is a combination of forward motion and free fall.

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gravitational pull is greater between two objects that have greater masses. If a student has a weight of 420 N on Earth, what is the student’s weight on the moon? (Moon’s gravity = 1/6 of Earth’s gravity) 420 x 1/6= 70N WEIGHT X GRAVITY= N

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**examples of projectile motion**

the path of a leaping frog the path of an arrow through the air the path of a pitched baseball If a tennis ball, a solid rubber ball, and a solid steel ball were dropped at the same time from the same height, which would hit the ground first? (Assume there is no air resistance.) ALL DROP AT SAME TIME

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**Which would hit the ground first?**

A crumpled piece of paper flat sheet of paper crumpled because there is more air resistance against the flat paper. A 5 kg object has less inertia than an object with a mass of 6 kg. (TRUE) According to Newton’s first law of motion, a moving object that is not acted on by an unbalanced force will remain in motion. (TRUE) action/reaction force pair: the forces between a bat and ball Why does a ball thrown horizontally follow a path that is curved downward? accelerated by gravity in the vertical direction only.

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**Newton’s Laws of Motion**

Newton’s 1st law- An object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force. Newton’s 2nd The acceleration of an object depends on the mass of the object and the amount of force applied. Newton’s 3rd law All forces act in pairs One object exerts a force on a second, the 2nd exerts an equal/opposite force on the first KNOW EXAMPLES OF ALL OF THESE!!!

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Path Orbit Curve Free fall

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