02/06 Mechanics and Further Mechanics Flashcards
define weight
the force due to gravity pulling two objects together, N
what is g
the acceleration due to gravity
define normal contact force
a force perpendicular to a surface when two objects are in physical contact
define Tension
a force which can be due to compression or stretching of a material
it always comes in pairs.
how does Tension work due to stretching
the materials molecules are pulled apart and an attractive electromagnetic force between the molecules pulls them back together.
how does Tension work due to compression
the material molecules are pushed together and a net repulsive electromagnetic force tries to push them further apart.
define Friction
a force that acts against motion between two surfaces in contact
parallel to motion in the opposite direction.
What does the size of a frictional force depend on?
- type of surface
- how hard the surfaces are pressed together.
define the moment force
turning effect on an object. It is the product of the distance perpendicular to the force and the force applied.
moment of a force about a point (Nm) =
force (N) x perpendicular distance from the force (m)
what is a couple
two forces that are equal and opposite do not act along the same line meaning there is no resultant force but still a turning effect.
what is the principal of moments
when an object is in equilibrium the sum of clockwise moments about any point equals the sum of anticlockwise moments about the same point.
what is the centre of gravity
the point at which we can take its entire weight to act
THERE IS NO MOMENT DUE TO WEIGHT.
what is the centre of mass
the point at which we can take the entire mass to be concentrated.
what is a Stable object
the centre of mass and line of action lies between the object’s base/supports.
Define mass
the amount of matter something contains, kg
define Distance
how much ground an object has covered during its motion (scalar quantity).
define Displacement
how far out of place an object is and the overall change in the object’s position (vector quantity).
define speed
rate of change of distance.
define velocity
rate of change of displacement.
define Acceleration
rate of change of velocity.
what do straight lines on a displacement time graph represent
constant velocity (if flat the velocity = 0).
how to work out the instantaneous velocity from a dt graph
draw a tangent and find the gradient.
how to work out the distance of journey from a dt graph
the sum of the slope heights including the negative (i.e. the max displacement is the distance travelled unless it started at a negative distance away that’s added to the max displacement away.)
displacement of journey from a dt graph
sum of slope heights including negatives.
how to get the max acceleration from a dt graph
find the initial and final velocity at two points by finding the gradient; divide by the time between the two points to get acceleration.
what is the gradient of a vt graph
acceleration.
what is the area under a vt graph
distance/displacement depending on negatives.
when can suvat equations be used?
when an object moves with constant uniform acceleration.
Suvat equation: X = X + XX
v = u + at.
Suvat equation: X^n = X^n + nXX
v^2 = u^2 + 2as.
Suvat equation: X = XX - nXX^n
s = ut - 1/2at^2.
Suvat equation: X = n(X +X)X
s = 1/2(u + v)t.
what is free fall
the only force acting on an object is gravity. Accelerate downwards at the same rate.
what is the definition of terminal velocity
the highest attainable velocity of an object as it falls through a fluid; the drag = weight.
terminal velocity can be different speeds i.e. a skydiver will have two different terminal velocities depending on if the parachute is open.
projectile motion
an object follows a parabolic path.
approaching a projectile’s question
resolve the initial velocity into horizontal and vertical components; acceleration only acts on the vertical component and is g.
horizontal distance can be easily calculated using the equation s = vt
define Momentum
a vector quantity that is the product of the mass and velocity of an object.
momentum, p (kgm/s) =
mass(kg) x velocity(m/s).
definition of impulse
the increase/decrease in momentum.
change in momentum =
Force x time.
what is the area under a force time curve
the total impulse acting and the total change in momentum produced.
what is the principal of conservation of momentum
in a closed system, the total momentum is constant so the momentum before a collision is equal to the momentum afterwards.
define recoil
the movement backwards due to conserved momentum.
define work done
the energy transferred whenever a force moves an object over a distance; scalar quantity measured in joules.
work done, w (J) =
force, F (N) * displacement in the direction of the force, s (m).
if the force and displacement are not in the same direction when calculating work done:
resolve the force; W = Fcosx * s.
define energy
the ability to do work.
what is the definition of 1 joule
the work done when a force of 1N moves through a distance of 1m in the direction of the force.
define power
rate of doing work.
power, P (W) =
= work done, w(J) / time taken, t (s) = force, F (N) * velocity, v (m/s).
define Kinetic energy
the energy an object has because of its motion.
K.E (J) =
1/2 * m* v^2.
define Potential energy
the energy stored in an object due to its position, state or shape; e.g. gravitational, chemical, elastic, electrical or nuclear.
GPE =
mgh.
Elastic potential energy =
= 1/2Fx = 1/2 kx^2.
define constant velocity
no resultant force and no work is done.
what is the principle of conservation of energy
energy can be transferred from one form to another, but it cannot be created or destroyed. The total amount of energy always remains the same.
define efficiency
the proportion of energy that is usefully transferred is called the efficiency of the machine.
efficiency =
useful out/total in.
linking k.e. and momentum K.E. =
p^2 / 2m.
define statics
objects in equilibrium.
define dynamics
objects that are accelerating/decelerating.
The resultant vector must be drawn where…
the bases of the other two vectors meet.
Why is calculated momentum not always correct?
At high speeds mass increases and the equations are only valid for non-relativistic speeds.
what is an elastic collision
100% of energy and momentum conserved.
define impulse
the change in momentum in a given time interval
what is newtons first law
an object will continue to move with uniform velocity unless acted upon by a resultant external force.
what is newtons second law
the rate of change of momentum of an object is directly proportional to the resultant force acting on it and will act in the same direction as that force.
what is newtons third law
If object A exerts a force on object B then object B exerts an equal and opposite force back on A.
conditions for a newtons third law pair
• forces must have the same magnitude
• forces act along the same line but in opposite directions
• forces act for/at the same time
• forces act on a different object
• forces are the same type.
define an inelastic collision
momentum is conserved , some energy is lost to the surroundings (dissipated)
