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Forces

Forces. push or pull that is capable of changing the state of motion of an object. Unit: Newton (N) 4.5N = 1 lb. Vector quantity (arrow of magnitude & direction) Forces in the same direction combines by addition. Forces in the opposite directions combine by subtraction.

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Forces

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  1. Forces • push or pull that is capable of changing the state of motion of an object. • Unit: Newton (N) 4.5N = 1 lb. • Vector quantity (arrow of magnitude & direction) • Forces in the same direction combines by addition. • Forces in the opposite directions combine by subtraction.

  2. Balanced Forces No change in motion. Opposite in direction and equal in size. Net force = 0 Unbalanced Forces One force is greater. “Net” force on an object is one direction. Types OR

  3. Friction • force that opposes motion. • depends upon weight, texture, & s.a. • Types • Sliding – solid objects slide over each other. • Rolling – wheels, ball bearings. • Fluid – “ability to flow”. Liquids & gases such as air/water resistance.

  4. Ways to Reduce? Lubricants – oil, grease, WD-40. Used in devices that have moving parts. Ex. engines Helpful? Motion keep from slipping & sliding Friction

  5. Newton’s Laws of Motion • relates forces to the motions of objects

  6. 1st: Concept of Inertia • Inertia = resistance to change (=mass). • An object at rest will remain at rest, object in motion will remain in motion unless a force acts upon it. • Describes motion when a balanced force acts on an object. (net force = 0)

  7. 2nd Law: Acc = Force/Mass • The acceleration of an object depends on the amount of force applied and the mass of the object. • Acceleration ~ Force (direct relationship) Acceleration ~ 1/Mass (inverse relationship) • Force is anything that can accelerate an object. • Describes the motion of an object when an unbalanced force acts on it.

  8. 3rd Law: All Forces Act in Pairs • In every interaction, forces always occur in pairs. • Whenever one object exerts a force on a second object, the second object exerts an equal & opposite force on the first. (FA due to B = FB due to A) • Hence, law of action – reaction

  9. Gravity • force of attraction between objects • Newton’s Law of Universal Gravitation • All objects in the universe attract each other by the force of gravity. • depends on the mass of objects & the distance between them.

  10. Acc. Due to Gravity • All falling objects accelerate at the same rate, regardless of their masses. • 9.8 m/sec/sec or 32 ft./sec/sec. • Free fall – considers only gravity & neglects air resistance.

  11. Air Resistance • Fluid friction • All falling objects meet air resistance. • Amount of air resistance depends upon: • speed, size, and shape of the object falling. • Terminal Velocity • air resistance = pull of gravity. Forces are balanced. No acceleration, falls at constant velocity.

  12. Weight vs. Mass • Weight • Measure of force of gravity. • Unit: Newton (N) • W = m x g • Mass • Amount of matter in a substance. • Unit: Kilogram (kg)

  13. Projectiles • Anything that’s thrown or shot through the air. • Curved path because of horizontal & vertical forces.

  14. Centripetal Force/Acc. • Centripetal Force – net force exerted toward the center of a curved path. • Centripetal Acceleration – acceleration toward the center of a curved or circular path.

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