Transcript CH 13
Chapter 13 Forces 13-1 Nature of Forces *Force: push or pull -gives nrg to an object -Newton said an object in motion stays in motion unless acted upon by an outside force (1st law of motion) *Friction: force that opposes the motion -sliding friction *when two solid surfaces slide over each other -amount depends on two factors 1. Weight 2. Types of surfaces -rolling friction *object rolls over a surface -oppose motion less than sliding ex: wheels and ball bearings -fluid friction *object moves through a fluid -all liquids and gases are fluids -usually opposes motion less than sliding friction *Lubricants: change sliding friction to fluid friction -friction can be helpful ex’s: ???? 13-2 Balanced and Unbalanced Forces *Balanced forces: opp in direction and equal in size -no change in motion -keeps an object moving at constant velocity *Unbalanced force: not opp and equal -always cause a change in motion 13-3 Force and Motion - 3 laws of motion explain rest, constant motion, and accelerated motion (Isaac Newton) st -1 Law of Motion *Inertia: tendency of objects to remain in motion or stay at rest -object at rest will remain at rest, and an object in motion will remain in motion, unless acted on by an unbalanced force(ex’s) nd -2 Law of Motion - Force = (mass)(acceleration) N = (kg) (m/s/s) -unbalanced force accel an object in the direction of that force - 1N = 1kg X 1 m/s/s Rd -3 Law of Motion *every action, there is an equal and opposite rxn -all forces come in pairs **Scooter Example** 13-4 Gravity -Free fall -All objects accel at the same rate, regardless of their mass *Gravity: attractive force b/all objects in the universe -Free fall ~near the surface of earth, accel due to gravity 9.8m/s/s -Any falling object meets air resistance *Terminal vel: no longer accel (120mph) -Projectile Motion *any object thrown in the air ~is always a curve -Once you release a ball the only force acting on it is gravity Orbital Motion *object that orbits another object ~it is a result of the object’s forward inertia and the downward pull of gravity on the object -Newton’s Law of Universal Gravitation *all objects in the universe attract each other by the force of gravity -The size of the force depends on: 1)mass 2)distance b/them 13-5 Weight and Mass -Weight: measure of the force of gravity on an object ~units: newton (N) ~w = m x g -Mass: amount of matter ~mass is constant