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Newton’s 2 nd Law and the Force of Gravity

Newton’s 2 nd Law and the Force of Gravity. SPH4C Findlay. The student will be able to state Newton’s Second L aw and apply it in qualitative and quantitative terms to explain the effect of forces acting on objects. How will the marble roll when it leaves the track?.

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Newton’s 2 nd Law and the Force of Gravity

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  1. Newton’s 2nd Law and the Force of Gravity SPH4C Findlay The student will be able to state Newton’s Second Law and apply it in qualitative and quantitative terms to explain the effect of forces acting on objects.

  2. How will the marble roll when it leaves the track?

  3. Review: Newton’s First Law • Which object has the most inertia? • A Feather • A textbook • Mr. Findlay • An Elephant • Fuzzy dice are hanging from the rear-view mirror of a car that is travelling forward at constant speed. The dice are: • Angled toward the back of the car • Angled toward the front of the car • Hanging straight down • It cannot be determined

  4. Review: Newton’s First Law • Fuzzy dice are hanging from the rear-view mirror of a car that is travelling forward and speeding up. The dice are: • Angled toward the back of the car • Angled toward the front of the car • Hanging straight down • It cannot be determined • Fuzzy dice are hanging from the rear-view mirror of a car that is travelling forward and slowing down. The dice are: • Angled toward the back of the car • Angled toward the front of the car • Hanging straight down • It cannot be determined

  5. Review: Newton’s First Law • A block of weight 4.0 N is suspended from the ceiling by a piece of string. What is the magnitude of the tension in the string? • 4.0 N • Less than 4.0 N • Greater than 4.0 N • Zero • A block of weight 4.0 N is being lifted at constant velocity by a piece of string. What is the magnitude of the tension in the string? • 4.0 N • Less than 4.0 N • Greater than 4.0 N • zero

  6. Newton’s 2nd Law of Motion and Weight SPH4C Findlay

  7. Newton’s Second Law of Motion • If the net force on an object is not zero, the object will be accelerated in the direction of the net force. • i.e. The more massive the object, the harder it is to change its motion (the higher its inertia).

  8. Example • A weightlifter lifts a 165-kg weight by exerting a force of 1.8 kN [up]. The force of gravity on the object is 1.6 kN [down]. Draw a FBD of the weight. What is the net force on the weight? What is the acceleration of the weight? 1.8 kN 1.6 kN

  9. Example Using Equations of Motion • A car is travelling at 25 m/s [forward] when the driver slams on the brakes and stops the car in 3.0 s. Calculate • the acceleration of the car • the net force needed to cause that acceleration if the mass of the car is 1200 kg.

  10. Weight (The Force of Gravity) • The formula can also be used to calculate the weight, , of an object, which represents the magnitude of the force of gravity acting on it. • If the acceleration, , is due to the acceleration due to gravity, , • Where the mass, , is measured in kg. • Weight is how much force of gravity is pulling down on an object. • Weight is therefore measured in Newtons. • The direction is always [down].

  11. Example • What is the weight of a 140-kg person?

  12. Practice • Calculate the weight of the objects of given mass below. • Oxygen gas molecule: 5.356 x 10-26 kg 5.25 x 10-25 N • Penny: 0.00235 kg 0.023 N • Tennis ball: 0.057 kg 0.56 N • Student: 61 kg 598 N • Newborn Elephant: 105 kg 1030 N

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