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Physics Chp4

Physics Chp4. Force - a push or pull Contact Force – friction, tension, shoving Noncontact Force – gravity, magnetism, electric Measured in newtons N = kgm /s 2. Free body diagrams Show the forces acting on an object for easy viewing and analyzing. Ex. Lifting a text book.

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Physics Chp4

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  1. Physics Chp4

  2. Force - a push or pull Contact Force – friction, tension, shoving Noncontact Force – gravity, magnetism, electric Measured in newtons N = kgm/s2

  3. Free body diagrams Show the forces acting on an object for easy viewing and analyzing. Ex. Lifting a text book

  4. Lift Force Flift BOOK Fg Gravitational Force If there is no acceleration how do the forces compare?

  5. Inertia – an objects tendency to resist a change in motion Mass – the quantitative measure of mass

  6. Newton’s First Law An object continues it’s motion unless acted upon by a net force Net force is the vector sum of all forces acting on the object

  7. If I lift my 1.5 kg text book causing it to accelerate upwards with a = 2.3 m/s2, how much force do I have to lift with? • Think about the earlier free-body diagram.

  8. Fnet = ma • Fnet = Flift – Fg • ma = Flift – m(9.81m/s2) • Flift = ma + m(9.81m/s2) • Flift = (1.5kg)(2.3m/s2) + (1.5kg)(9.81m/s2) • Flift =

  9. Newton’s Second Law • F = ma • Newton’s Third Law • Every action has an equal and opposite reaction

  10. If your car engine exerts a 4500 N force on it’s 1500 kg mass, how much acceleration will your car experience at full throttle?

  11. F = ma • 4500 N = (1500kg) a • a= 3 m/s2

  12. Normal Force • The force exerted by the object in contact with another object perpendicular to the surface usually due to gravity. • Ex. Your book on the table, the gravitational force is downward on the book but the normal force is upward from the table against the book. • What is the sum of those forces?

  13. Frictional Forces • Static vs Kinetic • Fs is not in the direction of Fn, they are perpendicular or at an angle to eachother.

  14. Kinectic Friction Always less than static friction μs > μk why? Both frictional forces oppose the motion of the object across the other object

  15. Ex. If my shoes have a static friction coefficient of 0.6 with the floor and I have a mass of 92 kg, what is the frictional force resisting my movement?

  16. Fn = mg

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