how can speed be calculated fro a distance-time graph?
the speed is equal to the gradient of the graph
what must be done to calculate speed at a given time from a distance-time graph for an accelerating object?
drawing a tangent to the curve at the required time
calculating the gradient of the tangent
equation for acceleration
acceleration (m/s^2) = change in velocity (m/s) / time taken (s)
how can distance travelled by an object be calculated from a velocity-time graph?
it is equal to the area under the graph
what is a scalar quantity?
a quantity with only magnitude and no direction
what is a vector quantity?
a quantity with both magnitude and direction
how can a vector quantity be drawn and what does this show?
as an arrow
the length of the arrow represents the magnitude
the arrow points in the associated direction
examples of vector quantities
force
displacement
velocity
examples of scalar quantities
temperature
time
mass
speed
distance
how do you calculate average speed for non-uniform motion?
average speed (m/s) = change in distance (m) / change in time (s)
what piece of apparatus may be used to record the time taken for a very fast object to move a given distance?
light gates
what is a force?
a push or pull acting on an object due to an interaction with another object
two categories force can be split into:
contact force (objects touching)
non-contact force (objects separated)
examples of contact force
friction
air resistance
tension
examples of non-contact force
gravity
electrostaticity
magnetism
what is the name given to the single force that is equivalent to all the other forces acting on a given object?
resultantforce
newton's first lawon a stationary object
if the resultant force on a stationary object is zero, the object will remain at rest
newton's first law on a moving object
if the resultant force on a moving object is zero, the object will remain at constant velocity
if an object changes direction but remains at a constant speed, is there a resultant force?
since there is a change in direction, it means there is a change in velocity so there must be a resultant force
when does an object fall with terminal speed?
when the upwards forces (air resistance) and the downwards forces (weight) are equal to each other
no resultant force, so constant speed
what happens to the magnitude of air resistance on a falling object when the velocity increases?
as velocity increases, the force of air resistance on the object will also increase
equation for newton's second law
resultant force (N) = mass (kg) x acceleration (m/s^2)
F = m x a
newton's second law
an object's acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass
what is inertia?
the tendency of an object to continue in its state of rest or uniform motion
an object's resistance to motion
what is intertial mass?
a measure of how difficult it is to change a given object's velocity
the ratio of force over acceleration
newton's third law
whenever two objects interact, the forces that they exert on each other are always equal and opposite
equation used to calculate an object's momentum
momentum (kg m/s) = mass (kg) x velocity (m/s)
P = m x v
unit used for momentum
kg m/s
kilogram metres per second
in a closed system, what can be said about the momentum before and after a collision?
the total momentum before is equal to the total momentum afterwards
equation linking change in momentum, force and time
force x time = change in momentum
F x Δt = P
F x Δt = m x Δv
explain how a seatbelt improves a passenger’s safety during a collision
the passenger must decelerate from the vehicle’s velocity at impact to zero, so they experience a force.
this force is equal to the rate of change of momentum.
seatbelts increase the time over which the force is applied, reducing the rate of change of momentum and therefore reducing the force felt by the passenger
what quantity is equal to the force experienced in a collision?
the rate of change of momentum
what does it mean if a force is said to have done 'work'?
the force causes an object to be displaced through a distance
what is the equation used to calculate work done? give appropriate units.
work done (J) = force (N) x distance (m)
W = F x d
under what circumstances is one joule of work done?
when a force of onenewton causes a displacement of onemetre