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Forces

Forces. Def – an action exerted on an object to change the object’s state of motion (resting or moving) Magnitude and direction Units: Newtons (N) Net force – total force on an object When there is a net force on an object, the object accelerates in the direction of the net force

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Forces

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  1. Forces • Def – an action exerted on an object to change the object’s state of motion (resting or moving) • Magnitude and direction • Units: Newtons (N) • Net force – total force on an object • When there is a net force on an object, the object accelerates in the direction of the net force • If net force = 0, then the object does not move

  2. Balanced forces • Net force = 0, no movement • Forces are balanced • An object standing still will not move • An object moving will not stop

  3. Unbalanced Forces • Net force is greater than zero, unbalanced force • Object will move

  4. Friction • Force that opposes motion between two surfaces that are in contact 2 types • Static – friction between two forces at rest, initial friction an object must overcome • Kinetic – friction between two moving objects • Static friction is usually greater

  5. Newton’s Laws • He was born the same year that Galileo died • Newton had ideas about motion, which he called his three laws of motion • Also had ideas about gravity, the diffraction of light, and forces • Physics and Math • Helped create Calculus

  6. First Law • Law of inertia • An object at rest will stay at rest and an object in motion stays in motion unless acted on by an external force • Inertia – tendency of an object to stay at rest or stay in motion • Mass is a measure of inertia • Small mass = less inertia • Seatbelts

  7. Second Law • The unbalanced force acting on an object equals the object’s mass times its acceleration • F=ma • Force is measured in Newtons (N) • 1 N = 1 kg x 1 m/s2 Q: What is the force necessary for a 1600 kg car to accelerate forward at 2.0 m/s2 ?

  8. 2nd Law Problem Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s2 . Using Newton's Second Law, compute how much force Mike is applying to the car.

  9. Third Law • For every action there is an equal and opposite reaction • Opposite in direction. • Whenever an object pushes another object it gets pushed back in the opposite direction equally hard • Example: Balloon full of air being released

  10. Force of Gravity • All objects in the universe attract each other through gravitational force • Mass increases – force of gravity increases • Distance increases – force of gravity decreases

  11. Force of Gravity • Free fall – only force of gravity is affecting an object • Calculate the acceleration at which an object free falls • Earth – 9.8 m/s2

  12. Force of Gravity • Weight is not the same as mass • Depends on gravity • Different locations have different gravities and therefore different weights • Force of gravity on an object is weight • w=mg • Newtons (N)

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