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Ch. 3 Forces & Motion

Ch. 3 Forces & Motion. 3.1- Force. Force - Ability to change motion(push or pull) Units of lb, N=km . m/sec 2 Mass - amount of matter in an object compared to a standard Weight - force acting on object (gravity) in lb or N

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Ch. 3 Forces & Motion

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  1. Ch. 3 Forces & Motion

  2. 3.1- Force • Force- Ability to change motion(push or pull) • Units of lb, N=km.m/sec2 • Mass- amount of matter in an object compared to a standard • Weight- force acting on object (gravity) in lb or N • Inertia- property of an object to resist change in state of motion • If forces are balanced= doesn’t move=equilibrium • Unbalanced forces=move • Forces always occur in pairs!!!!!

  3. Newton’s Laws of Motion • Newton’s First Law: • “AKA” Inertia • an object will stay at rest until acted on by an unbalanced force • In other words, things tend to keep on doing what they were doing in the first place unless you apply a force.

  4. Types of Energy • Kinetic Energy: energy of motion_____ • Potential Energy: Energy being stored due to its position; energy at rest. • Law of conservation of energy: energy is not created nor destroyed but changed from one type to another.

  5. Newton’s Laws of Motion • Newton’s Second Law: • force causes an object to accelerate while the object’s mass resists acceleration • F=ma • a=acceleration (m/s2), F= force (N), m=mass (kg) • EX. Lighter cars go faster

  6. 3.2 Gravity and Weight • Fw=mg • Fw= weight force (N) • m=mass (kg) • g=acceleration due to gravity (9.8 m/sec2) • Gravity- • Force pulling toward mass of planet • Depends on mass • Changes on other planets • On Earth= 9.8m/s2 • Weight- force created by gravity depends on mass • Force depends on mass they are not equal • Law of Universal Gravitation: force of attraction directly related to masses & indirectly related to distance

  7. Friction • Friction: • Reduce acceleration • Works against motion • When surfaces move against on another • Causes wear on parts • Types of friction: • Air friction- (air resistance) • Sliding friction (rub hands together) • Viscous friction- (oil in car engines & joint fluid) • Rolling friction- (wheel on road, ball bearings)

  8. 3.3 Newton’s Third Law • Newton’s 3rd Law: • For every reaction there is a reaction force equal in strength & opposite in direction • For every reaction there is an equal & opposite reaction • Can be + (move to right) or – (move to left) • Examples: rockets, stepping into a boat, throw a ball on a a skate board • Law of Conservation of Momentum: as long as interacting objects are not influenced by outside forces (friction), the total amount of momentum cannot change

  9. Can talk about 2 systems: • m1v1=m2v2 • Positive side shows movement • Ex: A 100 kg football player (fullback) moving at a speed of 3.5 m/sec collides with a 75 kg defensive back running at a velocity of 5 m/sec. Who gets thrown backwards? Why?

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