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Chapter 12

Chapter 12. Forces. http://www.youtube.com/watch?v=8zsE3mpZ6Hw http://www.youtube.com/watch?v=4NQbeZ0EXZQ http://www.youtube.com/watch?v=bkivr6bB-og&feature=related. Newton’s First Law of Motion. 1st Law of Motion(Law of Inertia). Objects in motion will stay in motion in a straight line

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Chapter 12

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  1. Chapter 12 Forces

  2. http://www.youtube.com/watch?v=8zsE3mpZ6Hw http://www.youtube.com/watch?v=4NQbeZ0EXZQ http://www.youtube.com/watch?v=bkivr6bB-og&feature=related

  3. Newton’s First Law of Motion 1st Law of Motion(Law of Inertia) • Objects in motion will stay in motion in a straight line • and objects at rest will stay at rest, unless acted on by • an outside force • Ex. Stack of books on a car seat. What happens • when you suddenly stop?

  4. Mass affects an objects inertia Inertia - objects resistance to a change in motion Increase mass = Increase inertia Lower mass = Lower inertia

  5. Seat belts and inertia • Seat belts work because they keep your body from flying forward. • If you get hit from behind will seatbelts or air bags help? No, you will fly back into the seat.

  6. Newton’s Second Law of Motion • Force is equal to the mass of an object and its acceleration. Force = Mass x Acceleration F = m x a Force is measured in Newtons 1 N = 1 kg x 1 m/s2 or 1kgm/s2 ( 1 lb is = to 4.45 N or 1 N is = to .225 lb)

  7. Newton’s Second Law of Motion • Newton’s second law explains how acceleration is dependant on force and mass.

  8. Newton’s Second Law of Motion

  9. Newton’s Second Law of Motion • Newton’s second law could also be written as: - When a force is applied to an object, the object accelerates in the direction of the greaterforce. OR • The acceleration of an object is directly proportional to the net force on the object and inverselyproportional to the object’s mass.

  10. Newton’s Second Law of Motion • Acceleration = net force/mass or a = F/m

  11. Gravity • Gravity - Force of attraction between two objects. - force of gravity depends on two variables: a. depends on mass • larger = more gravity (attraction) • smaller = less gravity (attraction)

  12. Gravity - force of gravity depends on two variables:(continued) b. depends on distance • closer = more gravity (attraction) • - further = less gravity (attraction)

  13. Weight • A measurement that can be taken because of gravity is weight. Weight– force of gravity pulling on the mass of an object. - weight is a force that can change. Mass never changes!

  14. Free Fall • when only gravity is acting on a falling object. • constant rate of acceleration. This is called gravitational acceleration (g) * g = 9.8 m/s² - which means everything accelerates as it falls at the rate of 9.8 m/s² each second!

  15. Free Fall and Weight • We can use this knowledge to mathematically find weight! Equation to find weight is same as force! Force (weight) = m a or weight = m X g (acceleration of gravity)

  16. Weight Ex. Find the weight of a 58 kg man on Earth. Weight = mg Weight = 58kg x 10 m/s2 = 580 kg m/s2 or 580 N Now find his weight on: Venus g=8.8 m/s2 Mars g= 3.7 m/s2 Neptune g=11.8 m/s2 58kg x 8.8 m/s2 = 510N 58kg x 3.7 m/s2 = 220N 58kgx11.8m/s2= 680N

  17. Newton’s 2nd Law • Newton’s 2nd law explains why heavy objects and light objects fall at the same rate. • -because if the mass is large, it is harder to accelerate (has more inertia). • So it takes more time to fall!

  18. Terminal Velocity • On Earth we have air resistance - causes friction, causing the falling objects to slow down Terminal Velocity - maximum velocity reached by a falling object. (320 km/h or 120 mph) - occurs when air resistance is equal to the gravitational acceleration.

  19. Terminal Velocity

  20. Projectile Motion • curved path an object follows when projected near the Earth’s surface.

  21. Projectile Motion - 2 components make up the path of projectile motion. Both are independent of each other. a. horizontal motion -force stays constant • vertical motion • -pulling it down at a rate of 9.8 m/s2

  22. Projectile Motion What if your object you are shooting at is falling too. Where should you aim? http://www.physicsclassroom.com/mmedia/vectors/mzng.cfm

  23. Projectile Motion -Orbiting objects are in projectile motion. - so they are NOT weightless or floating, they are just constantly falling!

  24. Newton’s 3rd Law of Motion • For every action there is an equal and opposite reaction. Forces act in pairs - don’t necessarily act on the same objects. Ex. Escaped balloon Action – air escaping from opening in balloon Reaction - balloon flies forward.

  25. Momentum • The product of the mass and velocity of a moving object. Momentum(p) = mass (kg) x velocity (m/s) p = kgm/s Ex. Calculate the momentum of a 6.00kg bowling ball Moving at 10.0 m/s down the lane. 6.00kg x 10 m/s = 60.0 kgm/s down the lane

  26. The Law of Conservation of Momentum • Total amount of momentum in a system is conserved. Ex.

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