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 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

3 laws of motion explain rest, constant motion, and accelerated motion 13-3 Force and Motion 3 laws of motion explain rest, constant motion, and accelerated motion (Isaac Newton)

-1st 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)

-2nd 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

-3Rd 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