Chapter 5 - work energy and power Flashcards
what is an equivalent phrase for work done
energy transferred
what is the equation for work done
work done = force x distance moved in the direction of the force
how does the equation change if the force is applied at an angle
w = f x cos(theta) x (x)
kinetic energy
energy due to the motion of an object with mass
GPE
energy of an object due to its position in a gravitational field
elastic potential energy
energy stored in an object as a result of a reversible change in shape
chemical energy
energy contained within the chemical bonds between atoms
electrical potential energy
energy of electrical charges due to their position in an electric field
nuclear energy
energy within the nuclei of atoms - it can be released when the particles within the nucleus are rearranged
radiant energy
energy associated with electromagnetic waves
sound energy
energy from the mechanical waves of atoms
heat energy
the sum of the random potential and kinetic energies of atoms
define conservation of energy
” energy can never be created or destroyed, only transferred from one form to another; the energy in a closed system remains constant”
equation for kinetic energy
and what proportionality does this give
KE = 1/2 x mass x velocity^2
KE is proportional to velocity^2
KE is proportional to mass
equation for GPE and value for g
GPE = m x g x change in height
if no resistive forces are present in a situation how can the transfer of GPE–> KE be modelled
mgh = 1/2mv^2 gh = 1/2v^2 v= sqrt(2gh)
define power
the rate of work done/energy transfer
equation for power (3)
units for power
P = W/t
P = E/t
P= Fv
measured in Js^-1 or watts (W)
define efficiency
the proportion of input energy which is transferred to useful energy
equation for efficiency
efficiency = (useful output energy/total input energy) x 100
what does 1Nm equal
1J
when do we tend to use the equation for power of P = fv
for an object moving at a constant velocity against a constant resistive force
what is energy
the capacity of an object to do work on another object
briefly describe how to calculate power for a motor lifting a load
- measure mass of load using a mass balance
- calculate weight of load using w = mg
- use the motor to lift the load
- measure the time taken using a stopwatch
- calculate power using (change in GPE)/time
