Mechanics Flashcards
When is an object in equilibrium?
No resultant force and no turning force (sum of moments is zero)
Define moment (including equation)
Moment = force x perpendicular distance from line of action of the force to the axis or point of rotation
Moment of a couple?
Moment of a couple =FD
When does a falling object reach terminal velocity?
When it’s weight (gravitational pull) is equal to the drag force and it no longer accelerates, it falls at a constant velocity
Newton’s First Law?
An object remains at rest/constant velocity unless acted on by a resultant force
Newton’s Second Law?
Include equations
Resultant force is proportional to the rate of change of momentum.
F = change in momentum/t
F=ma if m is constant and a is uniform
Newton’s Third Law?
Force exerted by A on B is in opposite direction, same type and equal to the force exerted by B on A
In an elastic collision, what is conserved?
Momentum is conserved
Kinetic energy is conserved
In an inelastic collision, what is conserved?
Momentum is conserved
Kinetic energy is NOT conserved
What does the area under a force time graph represent?
The impulse (change in momentum)
What does the are under a force displacement graph represent?
Fs, work done or energy transferred
In W=Fs, what conditions need to be true for it to hold?
Force must be constant and the displacement must be the distance in the direction of the force.
What does Hooke’s Law state?
Equation?
That the extension of a spring is proportional to the force applied provided the limit of proportionality is not exceeded
F=kx
What effect does a parallel spring system have on the spring constant?
kt = k1 + k2 + …
The spring constant increases
What effect does a series spring system have on the spring constant?
1/kt = 1/k1 + 1/k2 + …
The spring constant decreases
What effect does a parallel spring system have on the extension?
Extension decreases
What effect does a series spring system have on the extension?
Extension increases
What does the gradient of a force extension graph represent for something that obeys Hooke’s Law?
The spring constant
Define friction
Force that acts between two surfaces that meet
Define air resistance
A drag force experienced when moving through air
For circular motion, where is the object accelerating?
Towards the centre
In circular motion, ____ is always a tangent to the objects path
In circular motion, velocity is always a tangent to the objects path
What are the centripetal acceleration equations?
a = v^2 /r
a = w^2 r
What is the difference between angular velocity and angular frequency?
What is the equation?
Angular velocity is a vector and used for circles.
Angular frequency is a scalar and used for SHM and waves.
w=2 pi f
In circular motion, how do you work out the force acting towards the centre of the circle?
F= mv^2 /r
F=mw^2r
In a loop de loop, what will the reaction force be at the top?
R=(mv^2/r)-mg
In a loop de loop, what will the reaction force be at the bottom?
R=(mv^2/r)+mg
What is amplitude for SHM?
Magnitude of the max displacement (+ve)
What is displacement for SHM?
Distance from rest position (+ve or -ve)
What is frequency for SHM?
Number of oscillations per unit time
What is the period for SHM?
Time for one complete oscillation
SHM has:
an __ proportional to __ from equilibrium position
an a in ____ direction to displacement
SHM has:
an ACCELERATION proportional to DISPLACEMENT from equilibrium position
an acceleration in OPPOSITE direction to displacement
What is the acceleration equation for an object in SHM?
a=- w^2 x
What is the displacement equation for an object in SHM?
x=Acos(wx)
When is vmax in SHM?
At the equilibrium position
vmax =+- wA
When is amax in SHM?
At max displacement
amax = -w^2 A
For a simple pendulum, what is the time period?
What does it tell us?
T=2pi sqrt(L/g)
Where L is the length of the string.
T is independent of x or A
For a mass-spring system, what is the time period?
What does it tell us?
T=2pi sqrt(m/k)
Where k is the spring constant.
Bigger k, higher f and smaller T
Heavier mass, T increases
SHM graphs:
x against t is a ___ graph (starting from equilibrium position)
a sin graph
SHM graphs:
v against t is a ___ graph (starting from equilibrium position)
a cos graph
SHM graphs:
a against t is a ___ graph (starting from equilibrium position)
a negative sin graph
When in equilibrium position, a pendulum has:
- max __
- min __
In equilibrium:
- max kinetic energy
- min potential energy (0)
When at max displacement, a pendulum has:
- max __
- min __
At max displacement:
- max potential energy
- min kinetic energy (0)
In a vertical mass spring system:
When compressed,
- Ek is __
- Gpe is __
- Epe is __
In a vertical mass spring system:
When compressed,
- Ek is 0
- Gpe is max
- Epe is min
In a vertical mass spring system:
When at equilibrium,
- Ek is __
- Gpe is __
- Epe is __
In a vertical mass spring system:
When at equilibrium,
- Ek is max
- Gpe is 1/2 max
- Epe is 1/2 max
In a vertical mass spring system:
When most stretched,
- Ek is __
- Gpe is __
- Epe is __
In a vertical mass spring system:
When most stretched,
- Ek is 0
- Gpe is min
- Epe is max
