Topic 4 Dynamics - chapter 6 Flashcards
what is linear momentum?
it is the product of mass and velocity of an object.
p=mv where p= momentum- kgms^-1
m= mass- kg
v= velocity- ms^-1
it is a vector quantity.
its direction is the same as the direction of the object’s velocity.
what happens when 2 objects collide?
the momentum is transferred or shared.
what is the principle of conservation of momentum?
within a closed system(no external force is acting on the object), the total momentum in any diection is constant.
i.e,
total momentum before an interaction between bodies(e.g collision) = total momentum after the interaction.
what are the two types of collision?
perfectly elastic collision- the momentum and the kinetic energy is conserved.
inelastic collision- momentum is conserved; the kinetic energy may be converted in other forms such as sound or thermal energy or through the deformation of the object.
However, the total energy is conserved as stated in the principle of conservation of energy.
what is the relative speed?
relative speed is the speed of one object measured relative to the other.
how to calculate relative speed?
if the objects are travelling in opposite direction, add their speeds.
of the objects are moving in the same direction, subtract their speeds.
what is the relative speed in a perfectly elastic collision?
relative speed of approach = relative speed of separation.
what happens in a two-dimensional collision?
the components of their velocity must be equal in magnitude and opposite in direction, i.e, the resultant vector of these forces must be equal to the initial force’s vector.
how to show that the momentum is conserved in a vector diagram?
when momentum is conserved, the vectors form a closed triangle.
how to calculate moment in a 2-dimensional collision?
separate the horizontal and vertical component of the velocity of the objects. then compare each direction’s components. these components must be equal before and after the collision.
i.e, initial momentum in y-direction= final momentum
in y- direction
= (component of
momentum of 1st
object in y-direction)+
(component of 2nd
object in y-direction)
same with the components of x-direction.
OR
you can draw a vector diagram.
What are the Newton’s Law of motion?
1st law — an object will remain at rest or in a state of uniform motion unless a resultant force acts upon it.
2nd law — the resultant force acting on an object equals to the rate of change in momentum. the resultant force and change in momentum are in the same direction.
F= change in p/ change in t.
3rd law — when two bodies interact, the forces they exert on each other are equal in magnitude and opposite in direction.
what is the relationship between acceleration, mass and resultant force.
Newton’s 2nd law;
acceleration is directly proportional to resultant force, i.e, the more the resultant force, the larger the acceleration.
acceleration is inversely proportional to mass, i.e, the more the mass, the smaller the acceleration.
What is a special case of Newton’s 2nd law of motion?
newton’s 2nd law is , F = change in p/ change in t
which is equal to F = (mv-mu)/t
F= m(v-u)/t
since a= (v-u)/t
F= ma.
therefore, F=ma is a special case of F= change in p/t
where mass is constant.
