# Keywords and Equations

Keywords and Equations
Make sure you know the definition of all of these key words, phrases and
equations from the forces topic and any units. If they are formulae make
sure you know and can rearrange them to use them.
Keyword
Definition
Units
Average speed
Speed over a journey over a particular distance
and time
(Can have variations of instantaneous speeds
within it)
Speed at a particular moment in time
m/s
Instantaneous
speed
Speed equation
Positive distance
Negative
distance
Velocity
Stationary
Interaction Pair
Reaction
Up-thrust
Friction
Weight equation
Momentum
Equation
Change in
Momentum
Equation
Resultant force
Counter force
Kinetic energy
Gravitational
Potential energy
Work done
Equation
Speed = distance / time
(m/s)
(m)
(s)
Distance away from a starting point
Distance in opposite direction to positive
distance
Speed in a particular direction
When an object is at rest
Two forces that are equal and size and opposite
in direction. Both forces act on different
objects
Upward force produced by a surface when an
object is placed on it
Upward force produced by water when an
object floats on it
Force that acts in the opposite direction to
movement
Weight = mass x gravity
(N)
(kg)
(N/kg)
Momentum = mass x velocity
(kg m/s)
(kg)
(m/s)
Change in momentum = force x time force acts
(kg m/s)
(N)
(s)
Sum of all individual forces acting on an object
taking into account their direction
Force that acts in opposite direction to another
Energy possessed by a moving object
Energy that is stored in an object that will fall
due to gravity
Work done = force x distance
(J)
(N)
(m)
m/s
m
m
m/s
N
N
N
J
J
Conservation of
Energy
GPE equation
KE equation
Assuming that there in no friction and no air
resistance on a falling object
Loss in GPE = Gain in KE
GPE = weight x height
(J)
(N)
(m)
KE = &frac12; x mass x (speed)2
(J)
(kg)
(m/s)