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Chapter 10 – Forces

Chapter 10 – Forces. Chapter 10 – Forces. Section 3 – Newton’s 1 st and 2 nd Laws Standards 2.e – Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down or change direction)

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Chapter 10 – Forces

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  1. Chapter 10 – Forces

  2. Chapter 10 – Forces • Section 3 – Newton’s 1st and 2nd Laws Standards • 2.e – Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down or change direction) • 2.f – Students know the greater the mass of an object, the more force is needed to achieve the same rate of change in motion

  3. Newton’s 1st Law of Motion • Inertia (in ur shuh) – the tendency of an object to resist change in its motion • Newton’s First Law of Motion – an object at rest will remain at rest, and an object that is moving at constant velocity will continue moving at constant velocity, unless acted upon by an unbalanced force (called the law of inertia)

  4. F m a Newton’s 2nd Law • Newton’s 2nd Law – the net force on an object is equal to the product of its acceleration and its mass • Force = Mass x Acceleration • Acceleration = Force / Mass • Mass = Force / Acceleration

  5. Units • Mass – kilograms (kg) • Acceleration – meters per second per second (m/s2) • Newton – the force required to accelerate one kilogram of mass at 1 meter per second per second (kg.m/s2 which is a Newton)

  6. Force Problem Example • A 52 kg water skier is being pulled by a speedboat. The force causes her to accelerate at 2 m/s2. Calculate the net force that causes this acceleration. • Force = Mass x Acceleration • Force = 52 kg x 2 m/s2 • Force = 104 kg.m/s2 • Force = 104 N

  7. Force Problem Example • What is the net force on a 1,000-kg object accelerating at 3 m/s2? • Force = Mass x Acceleration • Force = 1000 kg x 3 m/s2 • Force = 3000 kg.m/s2 • Force = 3000 N

  8. Force Problem Example • What net force is needed to accelerate a 25-kg cart at 14 m/s2? • Force = Mass x Acceleration • Force = 25 kg x 14 m/s2 • Force = 350 kg.m/s2 • Force = 350 N

  9. Chapter 10 – Forces • Section 4 – Newton’s 3rd Law Standard • 2.e – Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down or change direction)

  10. Newton’s 3rd Law of Motion • Newton’s 3rd Law of Motion – states that if one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object • Newton called one force an action, and the other he called a reaction

  11. Action-Reaction Pairs

  12. Momentum • Momentum of an object is the product of its mass and velocity (p = m * v) • Momentum is the ‘quantity of motion’ • The unit for momentum is kg * m/s

  13. Conservation of Momentum • When two objects collide in the absence of friction, momentum is not lost • Law of Conservation of Momentum states that the total momentum of the objects that interact does not change • The total momentum of any group of objects remains the same unless outside forces act on the objects (friction is an example of an outside force)

  14. Momentum Problem Example • Which has more momentum: a 3.0-kg sledgehammer swung at 1.5 m/s, or a 4.0-kg sledgehammer swung at 0.9 m/s? • Momentum = Mass x Velocity • Momentum = 3.0 kg x 1.5 m/s • Momentum = 4.5 kg.m/s • Momentum = Mass x Velocity • Momentum = 4.0 kg x 0.9 m/s • Momentum = 3.6 kg.m/s • Momentum was greatest for 3.0 kg hammer

  15. Momentum Problem Example • A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has greater momentum? • Momentum = Mass x Velocity • Momentum = 0.045 kg x 16 m/s • Momentum = 0.72 kg.m/s • Momentum = Mass x Velocity • Momentum = 0.14 kg x 7 m/s • Momentum = 0.98 kg.m/s • Momentum was greatest for baseball

  16. Momentum Problem Example • What is the momentum of a bird with a mass of 0.018 kg flying at 15 m/s? • Momentum = Mass x Velocity • Momentum = 0.018 kg x 15 m/s • Momentum = 0.27 kg.m/s

  17. - Conservation of Momentum • In the absence of friction, momentum is conserved when two train cars collide.

  18. BRAIN BREAK! With your partner, discuss each of Newton’s 3 Laws and write a simple example of each

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