Bellringer
Answer the following questions in your science
journal:
If Wile E. Coyote and a boulder fall off a cliff
at the same time, which do you think will hit the
ground first? Would it matter if the cliff were very
high or particularly low? How could Mr. Coyote slow
down his fall?
Section 1 Gravity and Motion
Objectives
• Explain the effect of gravity and air resistance onfalling objects.
• Explain why objects in orbit are in free fall andappear to be weightless.
• Describe how projectile motion is affected by gravity.
Section 1 Gravity and Motion
Gravity and Falling Objects
• Gravity and Acceleration Objects fall to theground at the same rate because the accelerationdue to gravity is the same for all objects.
• Acceleration Due to Gravity As shown on the nextslide, for every second that an object falls, theobject’s downward velocity increases by 9.8 m/s.
Section 1 Gravity and Motion
Gravity and Falling Objects, continued
• Velocity of Falling Objects You can calculate thechange in velocity with the following equation:
∆v g t
• If an object starts at rest, this equation yields thevelocity of the object after a certain time period.
Section 1 Gravity and Motion
Air Resistance and Falling Objects
• Air resistance is the force that opposes the motion ofobjects through air.
• The amount of air resistance acting on an objectdepends on the size, shape, and speed of the object.
• The image on the next slide shows the effects of airresistance on a falling object.
Section 1 Gravity and Motion
Air Resistance and Falling Objects, continued
• Acceleration Stops at the Terminal Velocity Asthe speed of a falling object increases, air resistanceincreases.
• The upward force of air resistance continues toincrease until it is equal to the downward force ofgravity. The object then falls at a constant velocitycalled the terminal velocity.
Section 1 Gravity and Motion
Air Resistance and Falling Objects, continued
• Free Fall Occurs When There Is No AirResistance An object is in free fall only if gravity ispulling it down and no other forces are acting on it.
• A vacuum is a place in which there is no matter.Objects falling in a vacuum are in free fall becausethere is no air resistance.
Section 1 Gravity and Motion
Orbiting Objects Are in Free Fall
• Astronauts float in orbiting spacecrafts because offree fall.
• Two Motions Combine to Cause Orbiting Anobject is orbiting when it is traveling around anotherobject in space. The image on the next slide describeshow an orbit is formed.
Section 1 Gravity and Motion
Orbiting Objects Are in Free Fall, continued
• Orbiting and Centripetal Force The unbalancedforce that causes objects to move in a circular path iscalled a centripetal force.
• Gravity provides the centripetal force that keepsobjects in orbit.
Section 1 Gravity and Motion
Projectile Motion and Gravity
• Projectile motion is the curved path an objectfollows when it is thrown or propelled near the surfaceof the Earth.
• Projectile motion has two components—horizontalmotion and vertical motion. These components areindependent, so they have no effect on each other.
Section 1 Gravity and Motion
Projectile Motion and Gravity, continued
• Horizontal Motion is a motion that is parallel to theground.
• When you throw a ball, your hand exerts a force onthe ball that makes the ball move forward. This forcegives the ball its horizontal motion.
Section 1 Gravity and Motion
Projectile Motion and Gravity, continued
• Vertical Motion is motion that is perpendicular to theground.
• A ball in your hand is prevented from falling by yourhand. After you throw the ball, gravity pulls it downwardand gives the ball vertical motion.
Section 1 Gravity and Motion
Bellringer
Respond to the following question in your science
journal:
If you are sitting still in your seat on a bus that is
traveling 100 km/h on a highway, is your body at rest
or in motion? Explain your answer. Use a diagram if
it will help make your answer clear.
Section 2 Newton’s Laws of Motion
Objectives
• Describe Newton’s first law of motion, and explainhow it relates to objects at rest and objects in motion.
• State Newton’s second law of motion, and explainthe relationship between force, mass, andacceleration.
• State Newton’s third law of motion, and giveexamples of force pairs.
Section 2 Newton’s Laws of Motion
Newton’s First Law of Motion
An object at rest remains at rest, and an object inmotion remains in motion at a constant speed and in astraight line unless acted on by an unbalanced force.
• Newton’s first law of motion describes the motion ofan object that has a net force of 0 N acting on it.
Section 2 Newton’s Laws of Motion
Newton’s First Law of Motion, continued
• Part 1: Objects at Rest Objects at rest will stay atrest unless they are acted on by an unbalanced force.
• Part 2: Objects in Motion Objects will continue tomove with the same velocity unless an unbalancedforce acts on them.
• The image on the next slide shows how you can havefun with Newton’s first law.
Section 2 Newton’s Laws of Motion
Newton’s First Law of Motion, continued
• Friction and Newton’s First Law Friction betweenan object and the surface it is moving over is anexample of an unbalanced force that stops motion.
• Inertia and Newton’s First Law Newton’s first lawis sometimes called the law of inertia. Inertia is thetendency of all objects to resist any change in motion.
Section 2 Newton’s Laws of Motion
Newton’s First Law of Motion, continued
• Mass and Inertia Mass is a measure of inertia. Anobject that has a small mass has less inertia than anobject that has a large mass.
• So, changing the motion of an object that has a smallmass is easier than changing the motion of an objectthat has a large mass.
Section 2 Newton’s Laws of Motion
Newton’s Second Law of Motion
The acceleration of an object depends on the mass ofthe object and the amount of force applied.
• Newton’s second law describes the motion of anobject when an unbalanced force acts on the object.
Section 2 Newton’s Laws of Motion
Newton’s Second Law of Motion, continued
• Part 1: Acceleration Depends on Mass Theacceleration of an object decreases as its massincreases. Its acceleration increases as its massdecreases.
• Part 2: Acceleration Depends on Force An object’sacceleration increases as the force on the objectincreases. The acceleration of an object is always inthe same direction as the force applied.
Section 2 Newton’s Laws of Motion
Newton’s Second Law of Motion, continued
• Expressing Newton’s Second Law MathematicallyThe relationship of acceleration (a) to mass (m) andforce (F) can be expressed mathematically with thefollowing equation:
m
a
F
m
,
or
F
a
Section 2 Newton’s Laws of Motion
Newton’s Third Law of Motion
Whenever one object exerts a force on a secondobject, the second object exerts an equal and oppositeforce on the first.
• Newton’s third law of motion can be simply stated asfollows: All forces act in pairs.
Section 2 Newton’s Laws of Motion
Newton’s Third Law of Motion, continued
• Force Pairs Do Not Act on the Same Object Aforce is always exerted by one object on anotherobject. This rule is true for all forces, including actionand reaction forces.
• Action and reaction forces in a pair do not act on thesame object. If they did, the net force would always be0 N and nothing would ever move!
Section 2 Newton’s Laws of Motion
Newton’s Third Law of Motion, continued
• All Forces Act in Pairs—Action and ReactionNewton’s third law says that all forces act in pairs.When a force is exerted, there is always a reactionforce.
Section 2 Newton’s Laws of Motion
Newton’s Third Law of Motion, continued
• The Effect of a Reaction Can Be Difficult to SeeWhen an object falls, gravity pulls the object towardEarth and pulls Earth toward the object.
• You don’t notice Earth being pulled upward becausethe mass of Earth is much larger than the mass of theobject. Thus, the acceleration of Earth is much smallerthan the acceleration of the object.
Section 2 Newton’s Laws of Motion
Section 3 Momentum
Bellringer
This section is about momentum. Make a list of five
things that have momentum and a list of five things
that don’t have momentum. What must you do to
give an object momentum? What about removing
momentum?
Explain your answers in your science journal.
Objectives
• Calculate the momentum of moving objects.
• Explain the law of conservation of momentum.
Section 3 Momentum
Momentum, Mass, and Velocity
• The momentum of an object depends on the object’smass and velocity.
• Calculating Momentum The relationship ofmomentum (p), mass (m), and velocity (v) is shown inthe equation below:
p m x v
Section 3 Momentum
The Law of Conservation of Momentum
• The law of conservation of momentum states that anytime objects collide, the total amount of momentumstays the same.
• Objects Sticking Together After two objects sticktogether, they move as one object. The mass of thecombined objects is equal to the masses of the twoobjects added together.
Section 3 Momentum
The Law of Conservation of Momentum,continued
• The combined objects have a different velocitybecause momentum is conserved and depends onmass and velocity.
• So, when the mass changes, the velocity mustchange, too.
Section 3 Momentum
The Law of Conservation of Momentum,continued
• Objects Bouncing Off Each Other When twoobjects bounce off each other, momentum is usuallytransferred from one object to the other.
• The transfer of momentum causes the objects tomove in different directions at different speeds.
Section 3 Momentum
The Law of Conservation of Momentum,continued
• Conservation of Momentum and Newton’s ThirdLaw Conservation of momentum can be explainedby Newton’s third law.
• Because action and reaction forces are equal andopposite, momentum is neither gained or lost in acollision.
Section 3 Momentum
Forces and Motion
Use the terms below to complete the concept mapon the next slide.
forceprojectile motion
free fallair resistance
terminal velocitygravity
Concept Mapping
