9.1 Momentum and impulse Flashcards
What does the effect of a collision on two bodies depend on
Their mass and initial velocities
Who was the first person to realise that a force was needed to change the velocity of an object.
Sir Isaac Newton
How did Isaac Newton define the momentum of an object
Its mass * its velocity
How is the launch of a rocket planned
Using Newton’s laws of motion and his law of gravitation
However, these laws do not predict the existence of black holes which were a confirmed prediction of Einstein’s theory of general relativity
What is the unit of momentum
kg m s^-1
Momentum is a vector quantity, what is its direction the same as?
The direction of the objects velocity
For an object of mass m moving at velocity v, its momentum p=mv
p=mv
What is Newton’s first law of motion:
An object remains at rest or in uniform motion unless acted on by a force
What does Newton’s first law of motion tell us
A force is needed to change the momentum of an object. If the momentum is constant, there is no resultant force acting on it.
If a moving object gains or loses mass…
…its velocity would change to keep its momentum constant
What is Newton’s second law of motion
The rate of change of momentum of an object is proportional to the resultant force on it
The resultant force is proportional to the change of momentum per second
F=ma
Consider an object of constant mass m acted on by a constant force F
Its acceleration causes a change of its speed from initial speed u to speed v in time t without change of direction
Its initial momentum=mu and its final momentum=mv
Newton’s second law says force is proportional to change of momentum per second SO
F∝change of momentum/time taken=mv-mu/t=ma
Therefore F∝ma is F=kma where k is a constant
If the momentum of an object changes by Δ(mv) in time Δt, the force F on the object is given by the equation:
a=Δv/Δt
What is the unit of momentum
kg m s^-1
or
N s
Where does F=ma apply
Only to objects of constant mass
