Forces Flashcards
acceleration
rate of change of velocity
what does the gradient on a distance time graph show?
velocity
what does the gradient and area on a velocity time graph represent?
area- distance travelled
gradient- acceleration
what forces are acting on an object in freefall?
only g
stopping distance
total distance travelled from when the driver first sees a reason to stop to when the vehicle stops
stopping distance equation
thinking distance + breaking distance
thinking distance
distance travelled between the moment of realizing to brake and when the breaks are applied
thinking distance equation
speed x reaction time
braking distance
distance travelled from the moment the break is used and the car comes to a stop
what are the 4 most common forces on an object?
weight
normal contact force
tension
friction
inertia
an object’s resistance to a change in velocity
(momentum/velocity)
friction
a force that opposes motion
what are the two types of friction?
contact friction
fluid friction
mass
the amount of matter an object has
force
the rate of change of momentum
(F=ma)
Centre of gravity
the point at which the weight of the object may be considered to act
how do you find the centre of gravity of an object?
when applying a force to an object t not at the center of gravity it will rotate
whereas when pushed at its centre of gravity it will be pushed
what is the net force of an object when in equilibrium?
0
fluid
any substance that flows (eg water,air)
what does the magnitude of drag depend on?
speed of the object
cross sectional area of the object
roughness of the object
density of the fluid
(drag force ∝ speed squared)
terminal velocity
when the drag force on the object is equal and opposite to its weight (acceleration)
the moment of a force
the turning effect of a force about some axis or point
what is the principle of moments?
the sum of the clockwise moments is equal to the sum of the anticlockwise moments
couples
pair of forces working in opposite directions but not in equilibrium
(they are equal and opposite and they rotate but cause no translation)
torque
the moment of a couple
density
how much mass per unit volume
what is the air pressure at sea level?
100,000 pa
Archimedes principle
the upthrust exerted on a body immersed in a fluid is equal to the weight of the fluid that the body displaces
work done
force x distance moved in the direction of the force
energy
the capacity to do work
what is the principle of energy?
total energy for a closed system remains constant
energy cannot be created or destroyed
energy is transferred from one store to another
what does potential mean in physics?
hidden or stored
kinetic energy
energy associated with an object as a result of its motion
(KE=1/2 m (v squared)
gravitational potential energy
capacity for doing work as a result of an objects position in a gravitational field
(GPE=mgh)
power
the rate of work done
chemical energy
energy contained within the chemical bonds between atoms
elastic potential energy
energy stored in an object as a result of reversible change in its shape
electrical potential difference
energy of electrical charges due to their position in an electric field
nuclear energy
energy within the nuclei of atoms
EM energy
energy associated with EM waves stored within oscillating electric and magnetic fields
sound energy
energy of mechanical waves due to the movement of atoms
thermal energy
the sum of the random potential and kinetic energies of atoms in a system
tensile forces
a force that produces an extension
compressive forces
a force that shortens (compresses) an object
elastic deformation
the object will go to the original shape when the force is removed
plastic deformation
when the object has been stretched past its elastic limit and does not go back to its original shape
Hooke’s law
the extension of a spring is directly proportional to the force applied
what are the 3 forms of loading in alevel physics?
compression
tension
bending
how much an object can extend depends on what factors?
length
material
tension in wire
diameter
tensile stress
the force applied per unit cross sectional area of the wire
(It’s essentially pressure)
stress
an internal force induced in a metal in response to an externally applied force
tensile strain
the fractional change in the original length of a wire
necking
the point where a material starts to break
young’s modulus
the ratio of stress to strain of a particular material
newton’s first law
an object will remain at rest or continue to move with a constant velocity unless acted upon by a resultant force
newtons second law
the net force acting on an object is directly proportional to the rate of change of its momentum and in the same direction as the force
(net force ∝ rate of change of momentum)
newton’s third law
when two objects interact, they exert equal and opposite forces on each other
momentum
property of a moving object defined as the product of its mass and velocity
conservation of momentum
total amount of momentum before is equal to the momentum after the collision
what is a perfectly elastic collision?
a Collison where momentum, total energy and total KE are conserved
what is a inelastic collision?
a collision where only momentum and total energy is conserved but KE isnt
impulse
Change in momentum
product of force and time for which this force acts on an object
impulse of a force= change in momentum
F x change in t = change in P
