EX unit one: forces and motion Flashcards
distance travelled =
speed x time
unit of speed
metres/second or kilometres/hour
on a distance time graph what does the gradient or slope give?
the speed
on a distance time graph what does a horizontal line mean?
the object is stationary
acceleration =
change in velocity / time taken
what is the symbol for acceleration
a
what is the symbol for time
t
what is the symbol for velocity or speed
v
what is the symbol for distance
x or s
in a velocity time graph, what does the gradient or slope give?
acceleration
in a velocity time graph, what does the straight line mean?
constant acceleration
in a velocity time graph, what does the area under the graph show?
distance
final velocity squared =
initial velocity squared x 2 x acceleration x distance moved
what is the symbol for final velocity
v
what is the symbol for initial velocity
u
what are forces
pushes or pulls that one body exerts on another
normal reaction
the special name for the contact force that acts on an object pressing down on another object.
tension
in strings, cables, ropes etc. things that are being stretched.
friction
the force that opposes motion, either when you try to make something move or whilst it is moving
air resistance
friction between an object and the air (or gas) that its moving through
viscous drag
similar to air resistance, but occurs when an object is moving through a liquid.
upthrust
the upward force that liquids and gases exert on objects.
weight
the force that acts on a body because of gravity
magnetic
forces that magnets exert on other magnets or things made of iron
electrostatic
the force between electrically charged objects
unit of force
newtons (N)
are forces vector or scalar
vector
unbalanced forces acting on an object will cause…
a change in that object
e.g. accelerate, decelerate, change direction or change shape
how do you work out resultant force
subtract the forces acting on the object, and write the answer before the direction
hooke’s law
the extension of a spring is directly proportional to the force pulling it.
glass does not stretch but breaks. this means it is…
brittle
plasticine does stretch but does not return to its original shape. this means it is…
plastic
steel does stretch and does return to its original shape. this means it is…
elastic
what is the elastic limit
the point where the spring is overstretched and it will not return to its original length when the force is removed.
do rubber bands obey hookes law?
no, if you continue to stretch it the band will break.
force =
mass x acceleration
what does newton’s second law show?
the acceleration of an object is proportional to the force acting on it
to decrease the time and distance it takes for a car to stop by breaking, what must you increase
the friction force between the tyres and road surface (as shown through a = f / m , and how you cannot change the mass)
thinking distance
the distance you travel before you start to apply the brakes, which in turn, depends on your reaction time.
braking distance
the distance you travel while the car is decelerating to rest.
give thinking distance factors
alcohol and drugs, tiredness, visibility, distractions
give braking distance factors
worn tyres and brakes, icy and wet roads, speed
what is the approximate value for the gravitational field strength on earth
10 m/s squared
weight =
mass x gravitational field strength
what is the symbol for weight
W
what is the symbol for mass
m
what is the symbol for gravitational field strength
g
explain terminal velocity
when the size of the drag force caused by air resistance increases with speed - at some speed the size of the drag foce will be enough to balance the weight of the object. so the overall resuktant force on the object will be zero and it will no longer accelerates having reached its terminal/maximum velocity.
is acceleration a vector or scalar quantity
vector
are accelerating objects changing their velocity or their speed
they must be changing both
momentum
a measure of how easily an object can be brought to rest
is momentum a vector or scalar quantity
vector
what is momentum measured in
kilogram metres per second
kg m/s
what is mass measured in
g or kg
what is an elastic collision
one where no energy is lost
conservation of momentum is
the momentum of bodies colliding is always conserved.
total momentum of the two bodies before collision =
total momentum of the two bodies after collision
if one object is moving north and the other is moving south, what must you remember?
that the sign of one must be negative. it is up to you to choose whether to make north or south positive but you must stick to it.
force =
change in momentum / time taken
change in momentum is
final momentum - initial momentum
what is the symbol for momentum
p
what is the symbol for force
F
what are crumple zones
cars are designed with crumple zones to increase deceleration times, decrease forces and reduce injuries
what is newtons third law
for every action there is an equal and opposite reaction.
key features of every action-reaction pair of forces (involving newtons third law)
they are equal in size, opposite in direction, of the same type, and act on different objects
moment =
force x perpendicular distance from pivot
what is the moment of a force
it’s ‘turning effect’. levers are used to increase the turning effect of a force by increasing the distance between the force applied and the point around which the object will turn.
sum of clockwise moments =
sum of anticlockwise moments
if a beam is stationary, two conditions must be fulfilled:
the sum of the upward forces acting on the beam is equal to the sum of the downward acting forces.
the sum of clockwise moments acting on the beam about any point is equal to the sum of anticlockwise moments acting on the beam.
what is the centre of gravity
the whole weight of an object acts through one point of the object called its centre of gravity.
