Transcript Chapter 12
Chapter 12 - Forces 1 - Newton’s First and Second Laws 2 - Gravity 3 - Newton’s Third Law TN Standards • CLE.3202.3.2: Investigate and apply Newton’s three laws of motion • CLE.3202.4.1: Explore the difference between mass and weight • CLE.3202.4.2: Relate gravitational force to mass • CLE.3202.3.3: Examine the Law of Conservation of Momentum in real-world situations • CLE.3202.Math.1: Understand the mathematical principles behind the science of Physics Bellwork • How many laws of motion did Newton create? 1 – Newton’s st 1 and nd 2 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? Newton’s 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 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 QuickLab – Newton’s 1st 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 Newton’s 1st Law – In your notebook ( lab grade ) Newton’s Second Law • The unbalanced force acting on an object equals the object’s 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 Newton’s Second Law • Force is measured in Newtons ( 1 N = 1 kg x 1 m/s2 ) • For equal forces, a larger mass accelerates less • Acceleration depends on force and mass Newton’s Second Law • Force is measured in Newtons ( 1 N = 1 kg x 1 m/s2 ) • For equal forces, a larger mass accelerates less • Acceleration depends on force and mass 1 – Newton’s st 1 and nd 2 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? Bellwork • What is Newton’s First Law (in your own words) • What is Newton’s Second Law (in your own words) 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? 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 Law of Universal Gravitation • All objects in universe attract each other through the force of gravity • 𝑭=𝑮 𝒎𝟏 𝒎𝟏 𝒅𝟐 Law of Universal Gravitation • All matter is affected by gravity • Gravitational force increases with mass OR decreases with distance Free Fall • Without air resistance, all objects falling near Earth’s 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 ) Projectile Motion • Curved path of an object thrown, launched, kicked, or otherwise projected near Earth’s surface Projectile Motion • Two components – horizontal and vertical – Curved path when both are combined Projectile Motion • Orbiting is projectile motion 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? Bellwork • What is the difference between weight and mass? 3 – Newton’s 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? Action and Reaction Forces • Foot on Ball – ACTION • Ball on Foot – REACTION Newton’s Third Law • For every ACTION force there is an opposite and equal REACTION force Newton’s 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 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 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 Newton’s 3rd Law? Momentum • A property of all moving objects • Along a straight line, momentum is the product of an object’s mass and velocity – p = mv • Increases as mass and velocity increases • Force is related to change in momentum • How does moving the catcher’s glove back change the force needed to stop the ball? 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 3rd Law 3 – Newton’s 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?