Mechanics Flashcards
Scalars?
Qualities with Magnitude
Vectors?
Qualities with Magnitude and direction
Speed
rate of change of distance v = d/t (ms-1)
Velocity
rate of change of displacement v = displacement/s
Instantaneous speed
rate of change of distance at one particular tim\
Average speed
the speed over a period of time
Acceleration
rate of change of velocity a = ∆v/t (ms-2)
- Whether acceleration is +ve or -ve depends on the direction
- not if its speeding up or down
v = u + at
v = final velocity (ms-1)
u = initial velocity (ms-1)
a = acceleration (ms-2)
t = time (s)
v^2 = u^2 + 2as
v = final velocity (ms-1)
u = initial velocity (ms-1)
a = acceleration (ms-2)
s = displacement (m)
s = ut + 1/2at^2
t = time (s)
u = initial velocity (ms-1)
a = acceleration (ms-2)
s = displacement (m)
s = (v+u)t/2
t = time (s)
u = initial velocity (ms-1)
v = final velocity (ms-1)
s = displacement (m)
Range
How far it travelled horizontally
Range = Horizontal velocity x time of flight
Mass (m)
amount of matter in an object (kg) (does not ∆ if an object ∆ its position
Weight (W)
force of gravity acting on an object (N) (it will ∆ if an object ∆ its position)
W = mg
W = Weight (N)
m = Mass (kg)
g = gravity (9.81 Nkg-1 on earth)
Newton’s first law
“an object continues in uniform motion in a straight line or at rest unless a resultant external force acts”
Newton’s second law
“the resultant force on an object is proportional to the acceleration providing the mass of the object remains constant”
- bigger force -> bigger acceleration
- F = ma
Newton’s third law
“for every action on one object there is an equal but opposite reaction on another object”
F = ma
F = Force (N)
m = mass (kg)
a = acceleration (ms-2)
Ff ≤ μsR
Ff = static friction force (N)
μs = coefficient of static friction (max value = 1)
R = normal reaction force (N)
Static Friction = “about to move”
Ff = μdR
Ff = dynamic friction force (N)
μd = coefficient of dynamic friction (max value = 1)
R = normal reaction force (N)
Dynamic friction = sliding friction (not affected by speed) μd < μs
Ek = 1/2 mv^2
Ek = kinetic energy (J)
m = mass (kg)
v = speed (ms-1)
∆Ep = mg∆h
∆Ep = Gravitational potential energy (J)
m = mass (kg)
g = gravity
∆h = change in height
Ep = 1/2 k∆x^2
Ep = Elastic potential energy (J)
k = spring constant (Nm-1)
∆x = extension or compression (m) (change in length)
F (applied force (N)) = ∆x
W = Fs
W = work (J)
F = force (N)
s = displacement (m)
W = F s cosθ
W = work (J) (transfer of energy)
F = force (N)
s = displacement (m)
θ = angle between F & S
Force required to lift an object =?
Objects weight
P = Fv
P = power (W)(Js-1)
F = force (N) (constant)
v = velocity (ms-1) (constant)
Efficiency =
useful work out/total work in = useful power out/total power in
p = mv
p = linear momentum (kgms-1)(Ns)
m = mass (kg)
v = velocity (ms-1)
Conservation of momentum definition?
“the total linear momentum of a system remains constant provided no resultant external force acts (e.g. friction)”.
total p-before = total p-after
Elastic collision =
no kinetic energy is lost during the collision
inelastic collison =
kinetic energy is lost
Ek = p^2/2m
Ek = kinetic energy (J)
p = momentum (kgms-1)(Ns)
m = mass (kg)
Impulse =?
Change in momentum (F∆t = ∆p)
F = ∆p/∆t
F = Force (N)
∆p = change in momentum (impulse) (kgms-1)(Ns)
∆t = change in time
Explosions
Kinetic energy will always increase in an explosion
p=mv
big m = little v
little m = big v
projectile?
An object moving through air under the influence of only one force, gravity
