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Chapter 11 Newton’s Laws of Motion

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Chapter 10 breakdown Position Position Motion Motion Speed Speed Velocity Velocity Vector Vector Acceleration Acceleration

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11.1: Forces change motion Force: Force: A push or pull A push or pull Anytime you are changing the motion of an object you are using a force Anytime you are changing the motion of an object you are using a force Force is a vector Force is a vector Has both size and direction Has both size and direction Three types of forces: Three types of forces: Contact force Contact force Gravity Gravity Friction Friction

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Contact force: Contact force: Force created when one object pushes or pulls another object by touching it Force created when one object pushes or pulls another object by touching it The first object is applying a contact force The first object is applying a contact force Gravity: Gravity: The force of attraction between two masses The force of attraction between two masses Strength of the force depends on their masses Strength of the force depends on their masses Larger the mass = larger force Larger the mass = larger force Friction: Friction: A force that resists motion between two surfaces that are pressed together A force that resists motion between two surfaces that are pressed together

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Balanced and Unbalanced Forces Net force: Net force: The overall force acting on an object when all the forces are combined The overall force acting on an object when all the forces are combined If the net force is zero – the forces are balanced If the net force is zero – the forces are balanced Balanced forces have the same effect as no force at all Balanced forces have the same effect as no force at all Only an unbalanced force can change the motion of an object Only an unbalanced force can change the motion of an object

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An object with forces acting upon it can move at a constant velocity as long as the forces are balanced. An object with forces acting upon it can move at a constant velocity as long as the forces are balanced. Balanced forces cannot change an object’s speed or its direction. Balanced forces cannot change an object’s speed or its direction.

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Newton’s First Law of Motion Objects at rest remain at rest and objects in motion remain in motion with the same velocity, unless acted upon by an unbalanced force. Objects at rest remain at rest and objects in motion remain in motion with the same velocity, unless acted upon by an unbalanced force. The “motion” part of the Law will hold true in environments with no friction. The “motion” part of the Law will hold true in environments with no friction. The “rest” part of the Law will hold true in any environment. The “rest” part of the Law will hold true in any environment. AKA: Law of Inertia AKA: Law of Inertia

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Inertia Inertia: Inertia: The resistance of an object to a change in the speed or the direction of its motion The resistance of an object to a change in the speed or the direction of its motion Related to mass: Related to mass: When you measure the mass of an object you are also measuring the inertia of the object When you measure the mass of an object you are also measuring the inertia of the object

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11.2: Force and mass determine acceleration If you want to give two objects with different masses the same acceleration you must apply different forces to them. If you want to give two objects with different masses the same acceleration you must apply different forces to them. Newton’s Second Law of Motion: Newton’s Second Law of Motion: The acceleration of an object increases with increased force and decreases with mass The acceleration of an object increases with increased force and decreases with mass

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Newton’s Second Law contiued

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You can rearrange the formula to find acceleration or mass: You can rearrange the formula to find acceleration or mass: Acceleration = force divided by mass Acceleration = force divided by mass a = F ÷ m a = F ÷ m Mass = force divided by acceleration Mass = force divided by acceleration m = F ÷ a m = F ÷ a Force can make an object change direction Force can make an object change direction You can change the direction of an object without changing its speed You can change the direction of an object without changing its speed

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Centripetal Force Centripetal force: Centripetal force: Any force that keeps an object moving in a circle Any force that keeps an object moving in a circle The force ALWAYS points toward the center of the circle The force ALWAYS points toward the center of the circle No matter the mass of the object, if it moves in a circle, its force and acceleration are directed toward the center of the circle. No matter the mass of the object, if it moves in a circle, its force and acceleration are directed toward the center of the circle.

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11.3: Force acts in pairs Newton’s Third Law of Motion: Newton’s Third Law of Motion: Every time one object exerts a force on another object, the second object exerts a force that is equal in size and opposite in direction back at the first force Every time one object exerts a force on another object, the second object exerts a force that is equal in size and opposite in direction back at the first force For every action there is an equal but opposite reaction For every action there is an equal but opposite reaction Think about a balloon….what happens when you blow up a balloon and then release it? Think about a balloon….what happens when you blow up a balloon and then release it?

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Action and reaction pairs Action / reaction force pair: Action / reaction force pair: Force exerted upon one object and the force that the objects exerts back Force exerted upon one object and the force that the objects exerts back One force is the “action” force One force is the “action” force One force is the “reaction” force One force is the “reaction” force Action and reaction forces do not always result in motion Action and reaction forces do not always result in motion If you press against the wall, the wall resists the push with the same amount of force If you press against the wall, the wall resists the push with the same amount of force

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Action & reaction forces vs. balanced forces Action & reaction forces act on different objects: Action & reaction forces act on different objects: If you pull a backpack across the floor, you can feel the backpack pull on you with an equal force If you pull a backpack across the floor, you can feel the backpack pull on you with an equal force One force is acting on you, the other on the backpack One force is acting on you, the other on the backpack Balanced forces act upon a single object Balanced forces act upon a single object If you and your friend both pull on the backpack in opposite directions with equal forces, the backpack doesn’t move-both forces are exerted on the backpack If you and your friend both pull on the backpack in opposite directions with equal forces, the backpack doesn’t move-both forces are exerted on the backpack

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You can use Newton’s 3 laws to describe and predict motion: You can use Newton’s 3 laws to describe and predict motion: You can describe why something moves in the way that it does You can describe why something moves in the way that it does You can predict how an object’s motion will change by knowing the force applied You can predict how an object’s motion will change by knowing the force applied Newton’s 3 laws are not independent of one another – they are used together to explain the motion of objects Newton’s 3 laws are not independent of one another – they are used together to explain the motion of objects

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11.4: Forces transfer momentum Momentum (p): Momentum (p): The measure of mass in motion The measure of mass in motion Product of its mass and velocity (product means what in math?) Product of its mass and velocity (product means what in math?) Similar to inertia in regard to mass (the more mass the more momentum and inertia) BUT momentum also depends on how fast the object is moving Similar to inertia in regard to mass (the more mass the more momentum and inertia) BUT momentum also depends on how fast the object is moving momentum = mass times velocity momentum = mass times velocity p = mv p = mv

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Standard units of measure: Standard units of measure: mass = kg mass = kg velocity = m/s velocity = m/s momentum = kilogram-meter per second momentum = kilogram-meter per second Momentum is a vector Momentum is a vector has both size and direction (from the velocity) has both size and direction (from the velocity) kg m/s

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Transfer of momentum Collision: Collision: a situation in which two objects in close contact exchange energy and momentum a situation in which two objects in close contact exchange energy and momentum Generally action / reaction forces Generally action / reaction forces The object with the greater mass will have the greater change in velocity The object with the greater mass will have the greater change in velocity During a collision between two objects, each object exerts a force on the other During a collision between two objects, each object exerts a force on the other

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Conservation of momentum Conservation of momentum: Conservation of momentum: the total momentum of a system of objects does not change as long as no outside forces are acting on the system the total momentum of a system of objects does not change as long as no outside forces are acting on the system System: System: a collection of objects that affect one another a collection of objects that affect one another the colliding objects make up a system the colliding objects make up a system as they collide they both change velocity and momentum as they collide they both change velocity and momentum total momentum of the system remains unchanged as momentum is transferred not lost total momentum of the system remains unchanged as momentum is transferred not lost

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Finding total momentum objects moving in the same direction: objects moving in the same direction: add the momenta of the objects add the momenta of the objects objects moving in opposite directions: objects moving in opposite directions: subtract one momentum from the other subtract one momentum from the other

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