Mechanics Flashcards
What is the difference between a scalar and a vector quantity?
vectors have direction whereas scalars don’t
Is speed a scalar or vector?
scalar
Is velocity scalar or vector?
vector
Is distance scalar or vector?
scalar
Is displacement scalar or vector?
vector
What is Newton’s first law?
An object will remain at rest or at constant velocity unless acted on by an external force
What is Newton’s second law?
F=ma
What is Newton’s third law?
if object A exerts a force on object B, object B will exert an equal but opposite force on object A
When is an object at equilibrium?
When all vertical forces are equal and all horizontal forces are equal, the object will remain at rest or constant velocity
How do you resolve the vertical component of a vector?
Rsin(x) where x is the angle between the vector and the horizontal.
How do you resolve the horizontal component of a vector?
Rcos(x) where x is the angle between the vector and the horizontal.
What is a couple?
a pair of equal and opposite forces acting on a body but not along the same line
How do you calculate a moment?
moment = force x perpendicular distance from the pivot along the line of action
State the principle of moments.
when in equilibrium the total sum of the anti clockwise moment is equal to the total sum of the clockwise moment
What is the centre of mass?
the point at which all mass of the object acts
What is the moment of a couple?
the force x the perpendicular distance between the lines of action of the forces
Where is the centre of mass of an equal uniform shape, eg a square?
its centre
Define acceleration
the rate of change of velocity
What does the area under a distance - time graph represent?
velocity
What does the area under a velocity - time graph represent?
acceleration
What are the 5 suvat equations?
v^2 = u^2 + 2as v = u +at s = ut + 0.5at^2 s = vt - 0.5at^2 s = 0.5(u + v)t
What letter and value is given to the acceleration due to gravity?
g, 9.81
What is terminal velocity?
the constant velocity a freely falling object will reach when its forces reach equilibrium
Explain how terminal velocity is achieved.
when an object begins to fall its acceleration due to gravity exceeds its frictional forces due to air resistance. as it continues to fall, its velocity increases, and it collides more with particles in the air, increasing its air resistance. eventually air resistance will equal the force of its weight and it will continue at a constant (terminal) velocity
What name is given to the moment of a couple?
torque
How is momentum calculated?
p = mv
What name is given to the change in momentum?
Impulse
What is represented by the area under a force - time graph?
impulse
What is the rate of change of momentum?
force
What is meant by a completely elastic collision?
no loss of kinetic energy in the collision
What is the principle of the conservation of momentum?
if objects collide, the total momentum before the collision is the same as the total momentum after the collision (provided that no external forces - for example, friction - act on the system)
Which equation represents the amount of energy transferred?
W = Fscos(x)
What is efficiency?
the useful output power / total input power
x 100 to get percentage efficiency
What is the principle of the conservation of energy?
energy cannot be created nor destroyed it can only be transferred
Which equation can represent the change in potential energy?
change in potental E = mg x change in height
Which equation can represent kinetic energy?
Ek = 0.5mv^2
