P2.2 Flashcards
what is a force?
a push or pull acting on an object due to an interaction with another object
what are the two categories that all forces can be split into?
contact forces
non-contact forces
give three examples of contact forces
friction
air resistance
tension
give 3 examples of non-contact forces
gravitational forces
electrostatic forces
magnetic forces
what is the name given to the single force that is equivalent to all the other forces acting on a given object?
the resultant force
state newton’s first law for a stationary object.
if the resultant force on a stationary object is zero, the object will remain at rest.
state newton’s first law for a moving object
if the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in same direction)
if an object changes direction but remains at a constant speed, is there a resultant force?
since there is a change in direction, there is a change in velocity and 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.
state newtons second law in words
an objectors acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass
state the defining equation for newton’s second law
resultant force (N) = mass(kg) x acceleration(m/s^2)
F = ma
what is inertia
the tendency of an object to continue its state of rest or uniform motion
in other words, inertia is an objects resistance to motion
what is inertial mass?
a measure of how difficult it is to change a given object’s velocity
the ratio of force over acceleration
state newtons third law
whenever two objects interact, the forces that they exert on each other are always equal and opposite
state the equation used to calculate an objects momentum
momentum (kgm/s) = mass(kgs) x velocity (m/s)
P = mv
what is the unit used for momentum
kgm/s kilogram metres per second
what does it mean if a force is said to do ‘work’
the force causes an object to be displaced through a distance
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
state an equation linking change in momentum, force and time
force x time = change in momentum
explain how a seatbelt improves a passengers safety during a collision
the passenger must decelerate from the vehicles 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
under what circumstance is 1 joule of work done?
when a force of 1 newton causes a displacement of 1 metre
what is the equation used to calculate work done
work done(Joules) = force (newtons) x distance(metres)
