Topic 8- Forces doing work
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26 Terms
all objects have energy in their ___ energy store?
thermal
electrostatic energy store
energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart
when is energy transferred mechanically?
when a force acts on an object over a distance
when something changes in a system, ___ is transferred
energy
open system
allows the exchange of energy and matter to our from its surroundings
closed system
can exchange energy but not matter to or from its surroundings
isolated system
does not allow the transfer of matter or energy to or from its surroundings
change in energy in a closed system during energy transfers
in closed system energy transfers, there is no net change to the total energy
work can be done by: (2 things)
forces acting on an object
a current flowing through an electrical circuit
heating can be done by: (2 things)
heating particles
radiation
work is done when…
an object is moved over a distance by a force (in the direction of movement)
if a force is applied to an object, but doesn’t result in movement, is work done?
no
work done is the same as
energy transferred
work done formula
work = force x distance moved
gravitational store
the energy an object has due to its height in a gravitational field
change in gravitational potential energy formula
ΔGPE = m x g x Δh
kinetic energy store
the amount of energy an object has as a result of its mass and speed
kinetic energy formula
KE = ½ x m x v2
perfect energy transfer
no wasted energy
work done against air resistance, frictional forces and electrical resistance all result in…
heating (wasted energy)
power is the rate at which…
energy is transferred (therefore also work done per unit time)
power formula
P = E/t
power is measured in…
watts (W)
1 watt is the same as
1 Joule per second
efficiency equation in terms of power
efficiency = useful power output/total power input x 100
rearrange the efficiency equation to find total power input
total power input = useful power output x100 / efficiency