MECHANICS Flashcards
work
work is done when a force moves an object through a distance
work = force x distance
W = fd
energy
the ability to do work
the principle of conservation of energy
states that energy cannot be created or destroyed, but can only be converted from one form to another
kinetic energy
the energy a body has due to its motion
Ek = 1/2mv^2
potential energy
the energy a body has due to its height or position
Ep = mgh
mass
mass should be treated as a form of energy. the energy contained within a mass, m is given by
E = mc^2
a measure of how difficult it is to accelerate that body
power
- the rate at which work is done
- the rate at which energy is converted from one form into another
power = energy / time
efficiency
efficiency = output / input x 100
scalar
only have magnitude
e.g. mass, length, time
vector
have both magnitude and direction
e.g. velocity, acceleration, displacement
measurement of velocity and acceleration
ticker-tapes or light gates
velocity time graph
slope = acceleration
area under graph = distance travelled
speed
the rate of change of distance with respect to time
displacement
distance in a given direction
velocity
the rate of change of displacement with respect to time
acceleration
the rate of change of velocity with respect to time
equations of motion
- v = u+at
- s = ut + 1/2 at^2
- v^2 = u^2 + 2as
force
anything that causes an acceleration
the newton
the force that gives a mass of 1kg an acceleration of 1ms^-2
weight
the force of the earths gravity acting on an object
newtons 1st law of motion
every body will remain in a state of rest or travelling with a constant velocity unless an unbalanced force acts on it
newtons 2nd law of motion
when an unbalanced force acts on a body the rate of change of the bodys momentum is directly proportional to the force and takes place in the direction of the force
newtons 3rd law of motion
if body A exerts a force on body B, the body B exerts an equal but opposite force on body A. i.e action and reaction are equal but opposite
force & momentum
F = mv-mu/t i.e. force is equal to the rate of change of momentum
momentum
the product of a bodys mass and velocity
p = mv
friction
a force which tends to oppose motion.
principle of conservation of momentum
states that in any interaction between bodies, the total momentum before the interaction will equal the total momentum after the interaction, provided no external forces act upon the bodies.
m1u1 + m2u2 = m1v1 + m2v2
density
the density of an object is its mass per unit volume
pressure
force per unit area
pressure = force / area
pascal (Pa)
1 pascal = 1 newton per square metre
pressure in a liquid
P = pgh h = depth of water g = acceleration due to gravity p = density
archimedes principle
states that when an object is partially or completely immersed in a fluid it experiences an upthrust equal in magnitude to the weight of the fluid displaced
law of flotation
states that the weight of a floating body is equal to the weight of the fluid it displaces
boyles law
states that at constant temperature the volume of a fixed mass of gas is inversely proportional to its pressure
newtons law of universal gravitation
states that any two point masses in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
F = Gm1m2/d^2
G = universal gravitational constant
circular motion
an object in circular motion has a linear velocity, v, and an angular velocity
ω = θ/t
period
T = 2π / ω
centripetal acceleration
the acceleration of a body in circular motion. its direction is towards the centre of the circle
a = rω^2 // a= v^2/r
centripetal force
the force on a body in circular motion. its direction is towards the centre of the circle. the reaction to this force is away from the centre of the circle and is known as the centrifugal force
simple harmonic motion
any motion where the acceleration (a) of a particle is proportional to its distance (s) from an equilibrium position
a = -ω^2s
hookes law
states that when an object is bent, stretched or compressed by a displacement s, the restoring force f is directly proportional to the displacement - provided the elastic limit is not exceeded.
F = -ks
moment of a force
the moment of a force about an axis is equal to the magnitude of the force multiplied by the perpendicular distance from the axis to the line of action of the force
couple
created by two parallel forces with the same magnitude acting in opposite directions
conditions for equilibrium
- the sum of the force in any direction equals the sum of the forces in the opposite direction
- the sum of the moments about any point is zero
explain the distinction between speed and velocity
velocity is speed in a given direction
acceleration due to gravity
it is the acceleration of an object which is in freefall due to the gravitational pull of the earth
why does the value of g, the acceleration due to gravity, vary at different locations on the surface of the earth?
locations are at different distances from the earth’s centre
why is the acceleration due to gravity on the moon less than on earth
the mass of the moon is less than the mass of the earth
forces acting on a cheetah when its running
air resistence,
gravity
friction
instrument used to measure pressure
barometre
factors which effect the size of the gravitational force between two bodies
mass of the objects
distance between them
relationship between acceleration due to gravity, g and the distance from the centre of the earth
g is proportional to 1/d^2
why is it easier to turn a nut using a longer spanner than a shorter one
the distance from the fulcrum is greater therefore there is a greater turning effect
factors on which the potential energy of a body depends
mass
acceleration due to gravity
height
why is a fluorescent tube an efficient source of light
most of the electrical energy s converted to light energy
relationship between the period of the moon and the radius of its orbit
the period squared is proportional to the radius cubed
A body is said to be moving with simple harmonic motion if:
I. It’s acceleration is directly proportional to its distance from a fixed point on its path
II. It’s acceleration is always directed towards that point
