PHYS 105 Ch 6 Reading Notes

energy/oscillations - for exam 1

simple machine

any mechanical device that multiplies the effect on an applied force, such as a lever or pulley

pulley system

enables you to lift a weight a certain height by applying a force equal to only half the weight being lifted, however the rope must be pulled twice the distance the weight is lifted

work

force times distance; measured in joules (J); the force acts along the object’s line of motion

work equation

W = Fd

work output

always equals work input

mechanical advantage

the ratio of the output force to the input force of a simple machine; for a pulley it is 2

forces perpendicular to motion

do no work, such as normal force or gravity

power

the rate of doing work, found by dividing the amount of work done by the time; measured in watts

power equation

P = w/t

kinetic energy

the energy of an object related to its motion - one-half the mass multiplied by the square of the speed; work done is equal to the change in kinetic energy

kinetic energy equation

KE = 1/2mv²

negative work

work done by a force acting in a direction opposite to the object’s motion; W = -fd, where f is friction

doubling speed

quadruples the kinetic energy, because kinetic energy is proportional to square of the speed

potential energy

stored energy associated with a change in the position of an object rather than the object’s motion

gravitational potential energy

stored energy linked with the position of an object in a gravitational field rather than with the object’s motion

gravitational potential energy equation

PE = mgh, where mg is the weight and h is the height moved

elastic force

the force exerted by objects that can be deformed or stretched, such as a bowstring or spring

spring constant

a constant describing the relation between how far a string is stretched or displaced and how much force it takes to do the stretching: a stiff spring has a large spring constant

force exerted by a spring

equal to the spring constant multiplied by the distance stretched; F = -kx, where x is the distance stretched

applied force on a spring

must increase as distance x (either stretched or compressed) increases

elastic potential energy

potential energy in a system that depends on the displacement from equilibrium of an elastic object, like a spring

elastic potential energy equation

PE = 1/2kx²

conservative forces

forces such as gravity or the elastic forces that allow complete recovery of energy when work is done against them

conservation of energy

if the amount of mechanical energy (PE + KE) of a system remains constant through physical changes or processes (when no work is done on the system), then the energy is conserved

conservation of energy in symbols

if W = 0, E = PE + KE = constant

simple harmonic motion

the motion of a system whose energy changes smoothly from potential to kinetic energy and back again; symmetric about the point of equilibrium and graphed as a sinusoidal curve

period (T)

the time taken for one complete cycle, as of a wave

frequency (f)

the number of pulses, repetitions, or cycles per unit of time

amplitude

the maximum distance from the equilibrium point

restoring force

the force or system of forces that returns an object to equilibrium; must exist for any oscillation