Studied by 1 person
state the symbol equation to find momentum
p (kgm/s) = m (kg) x v (m/s)
state conservation of momentum definition
in a closed system
the total momentum before an event
is equal to the total momentum after the event
therefore energy is conserved
state an example of momentum in an event
collision
state what elastic collision is
when objects collide
and move in opposite directions
state what inelastic collision is
when objects collide
and move in the same direction
state what happens to kinetic energy in an elastic collision
kinetic energy is conserved
state what happens to kinetic energy in an inelastic collision
kinetic energy is not conserved
and it is wasted as heat energy
state what happens to mass and velocity of multiple objects in an elastic collison
the mass and velocity combine
state what happens to momentum in a collision
momentum is always conserved in a collision
explain how to complete calculations of a collision
write down the known mass and/or velocity of both objects
use these to calculate the momentum of one of the objects
the momentum will be the same before and after the event
use the equation p = m x v to find any unknown data
state what causes a change in momentum
when a force acts on an object that is moving
or able to move
state the symbol equation to find force using mass and acceleration
F (N) = m (kg) x a (m/s²)
state the symbol equation to find acceleration
a (m/s²) = Δv (m/s) / t (s)
state the equation to find force using acceleration, mass and time
F (N) = (m (kg) x Δv (m/s)) / t (s)
state the definition of force
rate of change of momentum
explain how air bags/seat belts work as safety features
air bags/seat belts absorb energy from collision by changing shape
for a given force upon impact, the air bags/seat belts absorb energy
and increase the time over which the force takes place
this increases the time taken for the change in momentum of the passenger and the vehicle to come to rest
the increased time reduces the force and thus the risk of injury to the passenger
explain why air bags are useful as safety features
they act as a soft cushion to prevent injury on the passenger
when they are thrown forward upon impact
explain why seat belts are useful safety features
they are designed to stop a passenger from colliding with the interior of a vehicle
by keeping them fixed to their seat in an abrupt stop
they are designed to stretch slightly
to increase the time for the passenger’s momentum to reach zero
and therefore reduce the force of the collision on the passenger
explain how gymnasium crash mats work as safety features
when an object lands on the crash mat with a large force
the soft landing means the object is in contact with the mat for a longer period of time
than if the mat was not there
this increases the contact time over which their momentum is reduced
creating a smaller impact force and a lower chance of injury
explain how cycle helmets work as safety features
when a cyclist’s helmet collides with a surface
the foam inside the helmet compresses upon impact
absorbing some of the energy during collision
slowing down the rate of change of momentum
this reduction in the rate of change of momentum leads to a decrease in the force experienced by the cyclist’s head
thus providing protection in case of collision
explain how cushioned areas in playgrounds work as safety features
when a child falls in the playground
the cushioned surface reduces the risk of severe injury by increasing the contact time of the child
the mat will be thinner than crash mats as children have a lower mass than adults
explain how increasing contact time in a collision protects passengers
causes rate of change of momentum to decrease
causes passenger to experience a smaller force
decreasing risk of injury
explain how increasing contact time in a plane landing is more comfortable for passengers
rate of change of momentum is slower
decreases force experienced by passengers
explain why some planes need longer runways to land safely
some planes have a larger mass
causing the aircraft to have more kinetic energy
due to it having more momentum
state what a scalar quantity is
quantity with magnitude
state what a vector quantity is
quantity with magnitude and direction
state the definition of a force
the rate of change of momentum
state the definition of a contact force
when a force is exerted when objects are physically-touching
state the definition of a non-contact force
when a force is exerted when objects are physically-separated
state examples of contact forces
friction
air resistance
tension
normal contact force
state examples of non-contact forces
gravitational force
electrostatic force
magnetic force
state what kind of quantity force is
vector
state what kind of force weight is
force acting on an object
due to gravity
state what causes the force of gravity close to earth
gravitational field strength around the earth
state what influences the weight of an object
gravitational field strength
of the area where the object is located
state word equation to calculate weight
weight = mass x gravity
state symbol equation to calculate weight
w = m x g
state where the weight of an object acts
single point
referred to as
the centre of mass
state the relationship between the weight and mass of an object
directly proportional
state how weight is measured
using a calibrated spring balance (newton meter)
state what a resultant force is
the sum of all forces acting on an object
state what causes work to be done
a force causing an object
to move through a distance
state when a force does work on an object
when the force causes
a displacement of the object
state word equation to calculate work done
work done = force x distance
state symbol equation to calculate work done
wd (J) = F (N) x s (m)
state what causes one joule of work to be done
when a force of one newton
causes a displacement
of one metre
state numerical relationship between joules and newton-metres
1 joule = 1 newton-metre
state what occurs when work is done against frictional forces acting on an object
temperature rise in the object
state forces involved in stretching an object
requires two forces
acting away from each other
state forces involved in compressing an object
requires two forces
acting towards each other
state forces involved in bending an object
requires two forces
acting towards each other
at different points on the object
or two forces at an angle to each other
explain why changing the shape of an object requires more than one force
because a single force applied would cause
the object to move in the direction
that force applied
deformation definition
change of shape
state when elastic deformation occurs
objects return to original shape
when stretching force is removed
state when inelastic deformation occurs
object remains stretched
and doesn’t return to completely to original shape
when stretching force is removed
state the relationship between the extension of an elastic object and the force applied
directly proportional
state Hooke’s law equation (word)
force = spring constant x extension
state Hooke’s law equation (symbol)
F (N) = k (N/m) x e (m)
state what happens when a force stretches/compresses an object
work is done
state where energy is stored when an object is stretched/compressed
elastic potential store
of the spring
state the numerical relationship between force and energy on a stretched/compressed object
work done and energy stored
in elastic potential store of the spring
is equal
state what changes the numerical relationship between force and energy on a stretched/compressed object
if the object is inelastically deformed
state what Hooke’s law is
linear relationship between force and extension
describe the difference between linear and non-linear relationships between force and extension
linear relationships on a force-extension graph
connote materials that obey Hooke’s law
portrayed by a straight line
non-linear relationships on a force-extension graph
connote materials that do not obey Hooke’s law
portrayed by a curve
explain how to calculate spring constant from a linear force-extension graph
rearrange Hooke’s law equation
to find spring constant
calculate the change in force
divided by the change in extension
a steep gradient means the material has a
small spring constant
a shallow gradient means the material has a
large spring constant
state symbol equation to calculate work done in stretching/compressing a spring
Ee (J) = 0.5 x k (N/m) x e2 (m)
state the variables in the investigation of force and extension
independent = force
dependent = extension
control = spring constant
state method to investigate force and extension
set up a clamp and stand, with a vertical ruler, spring and a pointer
align the pointer to a value on the ruler and record the initial length of the spring
add a 100g mass hanger to the spring
record the mass in kg and position of the pointer on the ruler in cm once the spring has extended
add a 100g to the mass hanger
record the new mass and position of the pointer on the ruler
repeat the process another 4 times
remove all the masses (including the mass hanger) and repeat the experiment three times
calculate the average length of the spring from your repeated experiments
analyse the results of the investigation of force and extension
force added to the spring is the weight of the masses
weight is calculated using equation: w = m x g
extension of the spring is calculated using equation: final length - original length
plot a graph of force (y-axis) against extension (x-axis)
draw a line of best fit
if the graph is linear, the spring obeys Hooke’s law
evaluate the investigation of force and extension
record readings from the ruler at eye level
to avoid parallax error
use a pointer to improve accuracy of ruler readings
to avoid random error
wait a few seconds for the spring to fully extend when mass is added
before taking the new reading length
state what causes an object to rotate
force or system of forces
state examples of rotation
person on see-saw
turning handle of a spanner
door opening and closing
state moment of force definition
turning effect of a force
state moment of force word equation
moment of force (Nm) = force (N) x distance (m)
state what happens to moments if an object is balanced
total anti-clockwise moment around a pivot
is equal
to the total clockwise moment around a pivot
state methods to transmit rotational effects of forces
simple lever
simple gear system
explain how levers transmit the rotational effects of forces
levers increase the size of the force
acting on an object
to make the object turn more easily
force applied to a lever must act further from the pivot
than the force has to overcome
state how to make a lever work better
increase size of the force applied
increase distance of force from pivot
explain how gear systems transmit the rotational effects of forces
gears multiply the effect of a turning force using moments
they consist of wheels with toothed edges
that rotate on an axle/shaft, which acts as a pivot
as one gear turns, the other must also turn
where gears meet, the teeth will move in the same direction
one of the gears will move clockwise
the other gear will move anti-clockwise
state what influences the moment of a gear in a simple gear system
although the force will be the same on the gears, the moment will not be
the moment depends on the size of the gear
which changes the distance of the teeth to the pivot
state what increases the moment of a gear
when it’s driven by a smaller gear
where the larger gear will rotate slower
than the smaller gear
but will have a greater moment
state what decreases the moment of a gear
when it’s driven by a larger gear
where the smaller gear will rotate quicker
than the larger gear
but will have a smaller moment
state what physical state a fluid can be
liquid or gas
state what pressure in fluid causes
force normal to any surface
state what a force acting normal means
force is acting at right angles
state symbol equation to calculate pressure at surface of a fluid
p (Pa) = F (N) / A (m²)
state word equation to calculate pressure at surface of a fluid
pressure = force / area
state word equation to calculate pressure due to a column of liquid
pressure = height x density x gravitational field strength
explain why pressure at a point in a liquid increases with the height of the water above that point
more liquid is above the point, causing pressure on the point to increase
as the excess pressure is caused by the increased weight of the liquid
pushing against objects immersed in the liquid
state where a submerged object experiences a larger pressure in a liquid
bottom surface of the liquid
state what resultant force pressure on a submerged object causes
upthrust
describe factors that influence floating
if upthrust on an object
is equal to or greater than
the object’s weight
or if the density of the object
is less than
the density of the fluid
describe factors that influence sinking
if upthrust on an object
is less than
the object’s weight
or if the density of the object
is more than
the density of the fluid
state what the atmosphere is
thin layer
of air
around the earth
state how altitude affects the density of the atmosphere
increasing altitude
decreases density
of the atmosphere
state what causes atmospheric pressure
air molecules
colliding with a surface
state what happens to the number of air molecules above a surface as altitude increases
decreases
state what happens to atmospheric pressure when altitude increases
decreases
state the numerical value of atmospheric pressure
100,000 Pa
state distance definition
how far an object moves
Note 
Flashcard (135)