chapter 13 physical science. chapter 13 forces and motion preview section 1 gravity: a force of...

Chapter 13

Physical Science

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

Forces and MotionChapter 13

Section 1 Gravity: A Force of AttractionChapter 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.

Section 2 Gravity and MotionChapter 13Air 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.

Section 2 Gravity and MotionChapter 13

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.

Section 2 Gravity and MotionChapter 13

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.

Section 2 Gravity and MotionChapter 13Projectile 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.

Section 2 Gravity and MotionChapter 13Projectile Motion and Gravity, continued

• Horizontal movement is movement parallel to the ground.

• Gravity does not affect the horizontal movement of projectile motion.

Section 2 Gravity and MotionChapter 13Projectile 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).

Section 2 Gravity and MotionChapter 13Orbiting 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.

Section 2 Gravity and MotionChapter 13Orbiting 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.

Section 2 Gravity and MotionChapter 13Orbiting 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.

Section 3 Newton's Laws of MotionChapter 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.

Section 3 Newton's Laws of MotionChapter 13Newton’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.


• 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.


• 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.


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.


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.

Section 3 Newton's Laws of MotionChapter 13Newton’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.


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.

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.

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.

• 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

• 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

• 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.

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!!!

• Path• Orbit• Curve• Free fall

chapter 13 physical science. chapter 13 forces and motion preview section 1 gravity: a force of...

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