Work And Power Flashcards
Can energy be created or destroyed?
Energy can not be created or destroyed…
Only transferred
What’s a closed system?
A system which experiences no external forces
GPE=
GPE= MassXgravityXheight
Ke=
Ke= 1/2 X Mass X v^2
What’s work done ?
Calculation for work done?
-the measure of energy transfer when a force (F) moves an object through a distance (d)
-work done = force (n) X distance moved in direction of force (m)
Why do mechanical processes waste a lot of energy?
Because they get hot due to friction ,energy is dissipated as heat —> rise in temp
What’s power?
What’s the equation for power?
-power is the rate at which energy is transferred
-power (w) = work done(energy transferred) /time taken
Equation for efficiency =
Efficiency = useful output / total input energy
In power 1 w = …
In power 1 w = 1j per second
What effect does doubling speed have on ke?
Doubling speed quadruples ke
Work done is equal too?
Work done is equal to energy transferred
Non contact forces…
-Gravitational attraction
-electrostatic attraction / repulsion
-magnetic attraction / repulsion
Contact forces…
-normal contact force
-friction
Vector has…
Size and direction
Scalar has…
Just size
Force that act on a sky diver? How..
-Air resistance.
-Weight
-initially sky river has no air reisistance, only force acting on him is weight.
-as he falls he accelerates (increasing air resistance)
-therefore resultant force decreases
-eventually weight and air resistance balance out so there’s no resultant force and terminal velocity is reached
Moment of a force (newton meters) =
Moment of a force (Nm) = force (N) X distance perpendicular to direction of force (M)
When does equilibrium occur ?
sum of anti-clockwise moments = sum of clockwise moments
What happens to the second gear when a gear supplying the force is connected to a second gear with fewer teeth?
Second gear will turn faster
With less force
In opposite direction
What’s does lubricatiom do?
Reduces friction so reduces unwanted energy transfer . Increases efficiency
