newtons laws of motion Flashcards
what is newtons first law
objects either stay at rest or move with constant velocity unless acted on by a force
an object moving at constant velocity is either …
acted on by no forces or the forces acting on it are balanced (so the resultant force is zero)
acceleration is always in the same direction as the …
resultant force
what is newtons second law
states that the net force acting on an object is equal to the rate change of momentum it experiences.
F=p/t
F=mv/t
F=m x v/t
F=ma
what does newtons second law tell us about what shappening to the object
object is experiencing change in momentum
object is experiencing change in velocity, speed ,direction or acceleration
there must be net force acting on object
why do heavier objects fall at the same rate as lighter objects
because for a mass in free fall
acceleration=the force of gravity mg / mass m
=g
therefore the rate at which objects fall is independent the rate of m
A vehicle of mass 600 kg accelerates uniformly from rest to a velocity of 8.0ms^-1 in 20s. Calculate rhe force needed to produce this acceleration.
a=v-u/t
a=8-0/20
a=0.4ms^-2
F=ma
F=600x0.4
F=240N
the measure of g depends on its …
location/planet
the mass of an object is a measure of its …
inertia which is its resistance to change of motion
how to find the acceleration of object acted on by two opposite forces
F1-F2=ma
how to work out the resultant force or car towing trailer
F-T=Ma
T=ma
F=Ma + ma
what equation d you use when working on rocket problems
T=mg + ma
T(thrust)
what equation do you use when lift is moving at constant velocity
T=mg
T(tension)
what equation do you use if lift is moving up and accelerating
T=mg + ma
T-mg=ma
what equation do you use if a lift is moving and down accelerating
mg = ma + T
mg-T=ma
how do you approach pulley problems
work out equation for both masses using
T-mg=ma &
Mg-T=Ma
and then do simultaneous equations
what does drag force depend on in a fluid
shape of object
its speed
the viscosity of liquid (how easily an fluid flows past a surface)
what is terminal speed
maximum speed a object can reach when all the forces are balanced
what is needed for terminal speed to be reached when an object falls
drag force has to be equal and opposite to the objects weight so its acceleration is zero and so its speed remains constant when it falls
how do you work out the resistive force
by adding all the drag forces acting on the object
what is the resultant force of a objet when resistive forces act on it
F(motive)-F(resistive)=ma
what is thinking distance
distance travelled in the time it takes to react
what is braking distance
distance travelled by a car in the time it takes to stop safely from when brakes are first applied
stopping distance
thinking distance + braking distance
A car can only move forwards
by pushing … on the road
backwards
When you push … on the ground, the ground exerts an equal and opposite force on you that enables you to move forward.
backwards
braking distance depends on …
the speed of the vehicle the instant the brakes are applied
on an icy or greasy road skidding is more likely because
the limiting frictional force between the road and the tyres is reduced from its dry value
what is newtons third law
for every force acting on an object, the object will exert an equal and opposite force on its cause
