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Chapter 12 - Forces 1- Newtons First and Second Laws 2- Gravity 3 - Newtons Third Law

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TN Standards CLE : Investigate and apply Newtons three laws of motion CLE : Explore the difference between mass and weight CLE : Relate gravitational force to mass CLE : Examine the Law of Conservation of Momentum in real-world situations CLE.3202.Math.1: Understand the mathematical principles behind the science of Physics

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Bellwork How many laws of motion did Newton create?

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1 – Newtons 1 st and 2 nd Laws Key Questions: What makes an object speed up, slow down, or change directions? What determines how much an object speeds up or slows down?

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Newtons First Law An object at rest remains at rest and an object in motion maintains its velocity unless it experiences a net force Objects change their state of motion only when a net force is applied Objects tend to maintain their state of motion

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Inertia Laziness of all matter based on mass Is the tendency of an object to stay at rest or to move at constant velocity ( if moving ) Seat belts and car seats

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QuickLab – Newtons 1 st Law Place an Index Card over a glass; Coin on card Flick the card sideways off the glass – what happens to the coin? Does coin move with Index Card? Repeat but slowly pull card sideways – what happens to the coin? Explain the results using Newtons 1 st Law – In your notebook ( lab grade )

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Newtons Second Law The unbalanced force acting on an object equals the objects mass times its acceleration Net force equals mass times acceleration – F = ma Unbalanced force on an object determines how much an object speeds up or slows down

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Newtons Second Law Force is measured in Newtons ( 1 N = 1 kg x 1 m/s 2 ) For equal forces, a larger mass accelerates less Acceleration depends on force and mass

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Newtons Second Law Force is measured in Newtons ( 1 N = 1 kg x 1 m/s 2 ) For equal forces, a larger mass accelerates less Acceleration depends on force and mass

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1 – Newtons 1 st and 2 nd Laws Key Questions: What makes an object speed up, slow down, or change directions? What determines how much an object speeds up or slows down?

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Bellwork What is Newtons First Law (in your own words) What is Newtons Second Law (in your own words)

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2 – Gravity Key Questions: 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?

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Weight and Mass Force on an object due to gravity is WEIGHT – Weight is measured in Newtons Free-fall acceleration is a constant acceleration all objects on earth experience Weight is equal to mass times free-fall acceleration – w = mg

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Law of Universal Gravitation

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All matter is affected by gravity Gravitational force increases with mass OR decreases with distance

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Free Fall Without air resistance, all objects falling near Earths surface accelerate at the same rate regardless of their mass Due to the Law of Gravitation Air resistance can balance weight – EXAMPLE : Leaf falling at constant velocity – TERMINAL VELOCITY ( max velocity obtained )

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Projectile Motion Curved path of an object thrown, launched, kicked, or otherwise projected near Earths surface

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Projectile Motion Two components – horizontal and vertical – Curved path when both are combined

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Projectile Motion Orbiting is projectile motion

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2 – Gravity Key Questions: 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?

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Bellwork What is the difference between weight and mass?

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3 – Newtons Third Law Key Questions: What happens when an object exerts a force on another object? How do you calculate the momentum of an object? What is the total momentum after objects collide?

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Action and Reaction Forces Foot on Ball – ACTION Ball on Foot – REACTION

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Newtons Third Law For every ACTION force there is an opposite and equal REACTION force

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Newtons Third Law Forces always occur in pairs Forces in a force pair do not act on the same object – Do not cancel each other Equal forces do not always have equal effects

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QuickLab – Action/Reaction Forces Hang a 2 kg mass from a spring scale Observe and record the reading on the spring scale With the mass on the first scale, link a second scale to the first Observe/record readings from both scales

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QuickLab – Action/Reaction Forces QUESTIONS: What are the action and reaction forces in the spring scale-mass system that you have constructed? How did the readings on both scales compare in the last step? Explain how this demonstrates Newtons 3 rd Law?

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Momentum A property of all moving objects Along a straight line, momentum is the product of an objects mass and velocity – p = mv Increases as mass and velocity increases Force is related to change in momentum How does moving the catchers glove back change the force needed to stop the ball?

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Conservation of Momentum The total amount of momentum in an isolated system is conserved Total momentum of two or more objects after a collision is the same as the momentum before Explained by 3 rd Law

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3 – Newtons Third Law Key Questions: What happens when an object exerts a force on another object? How do you calculate the momentum of an object? What is the total momentum after objects collide?

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